
To appear (with commentaries) in:
    Philosophy Psychiatry and Psychology


          TOWARDS A DESIGN-BASED ANALYSIS OF EMOTIONAL EPISODES

               Ian Wright, Aaron Sloman & Luc Beaudoin(*1)

                    Cognitive Science Research Centre
                       School of Computer Science
                        University of Birmingham
                             September 1995

                                Abstract
           The design-based approach is a methodology for investigating
       mechanisms capable of generating mental phenomena, whether
       introspectively or externally observed, and whether they occur in
       humans, other animals or robots. The study of designs satisfying
       requirements for autonomous agency can provide new deep theoretical
       insights at the information processing level of description of
       mental mechanisms. Designs for working systems (whether on paper
       or implemented on computers) can systematically explicate old
       explanatory concepts and generate new concepts that allow new and
       richer interpretations of human phenomena. To illustrate this,
       some aspects of human grief are analysed in terms of a particular
       information processing architecture being explored in our
       research group.
           We do not claim that this architecture is part of the causal
       structure of the human mind; rather, it represents an early stage
       in the iterative search for a deeper and more general architecture,
       capable of explaining more phenomena. However even the current
       early design provides an interpretative ground for some familiar
       phenomena, including characteristic features of certain emotional
       episodes, particularly the phenomenon of perturbance (a partial
       or total loss of control of attention).
           The paper attempts to expound and illustrate the design-
       based approach to cognitive science and philosophy, to demonstrate
       the potential effectiveness of the approach in generating
       interpretative possibilities, and to provide first steps towards
       an information processing account of `perturbant', emotional
       episodes.
  ___________________________________
  *1 The first two authors are at the University of Birmingham.  The
third author is now at Newbridge Microsystems, Canada.  This pa-
per was written by the first two authors, making considerable use of
ideas developed with the third author and reported in his PhD Thesis
(Beaudoin 94)

1      Introduction

The human mind, and its underlying engine, the brain, are incredibly
complex collections of mechanisms of many kinds, produced over millions
of years of evolution. As a result of its origins there are several
levels of control, of varying degrees of sophistication. Some, like
reflex arcs, are shared with many other organisms. Some, like the
mechanisms involved in arousal of various kinds, e.g. those involving
the limbic system, seem to be shared with many other mammals. Some, like
cortical mechanisms involved in the ability to long for recognition, the
ability to enjoy the admiration and respect of others, the ability to be
thrilled by a mathematical discovery, and the ability to grieve at the
death of a friend, require sophisticated cognitive capabilities, which
may be unique to humans. Because many researchers into emotions do not
clearly distinguish the different types of phenomena, there is much
confusion about what is being studied and what is explained by various
theories. Our concern is primarily with mental processes that are
typically to be found in human beings, which involve high level
cognitive functions and which often have social consequences. They may
also, in fact, involve older more primitive mechanisms, though those are
not the concern of this paper. (A complete theory of the human mind
would have to include them.)

     This paper has two main goals:  (a) to illustrate the design-based
approach to the study of some `higher level' human mental processes;
and (b) to make theoretical progress towards a design-based account of
certain emotional episodes, namely those that involve a partial or total
loss of control of thought processes. Our work derives ultimately from
suggestions in (Simon 67), though we have extended and generalised
Simon's ideas.

     We try to show how a certain sort of information processing
architecture, extending ideas in Artificial Intelligence, can serve as a
new explanatory ground for some well-known emotional phenomena. Whether
the proposed outline architecture is correct, how it might be
implemented in neural mechanisms and what the implications of further
refinements will be, remain questions for future investigation. The
architecture certainly does not yet account for all aspects of grief,
and it also leaves unexplained other important mental phenomena which
points to the need for extensions to the architecture, which we shall
continue to explore.

     Section 2, which follows this introduction, is primarily
theoretical: subsection 2.1 introduces key ideas of the design-based
approach to the study of mind, including the idea of a `broad but
shallow' architecture. Subsections 2.2 and 2.3 sketch our high level
design for autonomous agents, including the distinction between highly
parallel `automatic' attention-free processing and resource-bound
`management' and `meta-management' processes (Beaudoin, 94).
Allocation of `management' resources is one aspect of attention (the
management of thought).

     Section 3 applies our theory to a concrete example: subsection 3.1
presents an example of a first-hand account of human grieving. We
identify certain characteristic features of grieving to be explained
(along with other phenomena which we ignore) by any complete theory of
human emotions. Subsection 3.2 introduces the notion of self- control
and limits to self-control. Subsection 3.3 introduces the type of
personal attachment which plays a decisive role in states of grieving.


                                         2

Subsection 3.4 explains in outline how the theory provides
architecturally grounded explanations for the phenomena of grief.

     Section 4 provides concluding comments and reservations.


2      The  design-based  approach

This  section  outlines  the  design-based  approach,  sketches  an
architecture for autonomous resource-bounded agency, and introduces the
notion of a `hierarchy' of dispositional control states.  Some known
gaps in the theory are discussed later.



2.1      Ontology and the design-based approach

We assume (a) that information-processing architectures exist, are
implemented on human brains, and mediate both internal and external
behaviour; and (b) that our methodology allows a systematic approach
towards high level functional congruity between artificial,  explicitly
designed architectures and certain important aspects of evolved,
naturally occurring architectures, despite differences in low level
implementation details.

     Claim (a) underlies much contemporary Cognitive Science and has
been argued for or presupposed by many theorists (e.g., see (Miller
et al., 70), (Johnson-Laird, 88), (Simon, 67, 69, 95); and (Palmer &
Kimchi, 84) for different sub-theses).

     Claim (b) is more contentious and depends on finding appropriate
levels of abstraction.  There are other examples of congruity at high
levels despite low level differences. Two physically quite different
computing systems may both implement the same virtual machine
architecture (e.g., both may be Prolog systems, or both may implement
internet  utilities,  including  mail,  news,  telnet  and  the  World
Wide Web). Similarly, it is often taken for granted that general
principles of feedback control apply both to natural and artificial
systems. What we need to add to this, following much work in Artificial
Intelligence, and the ideas in Simon (67), is a level of explanation
that involves richer and more profound forms of control of both external
and internal behaviour using richer semantic structures and new sorts of
control architectures to support various kinds of motivational
processes (e.g., see Simon 67, Sloman & Croucher 81, Sloman 87, Beaudoin
& Sloman 93, Sloman 93a, 93b, Beaudoin 94, Sloman 94, Sloman, Beaudoin &
Wright 94.)

     Brains appear to support several rich ontologies at different
levels of abstraction.  In computing systems, ontologies are often
`stacked' in  layers  of  implementation.   For  instance,  a  word
processor  package that manipulates pages, paragraphs, sentences, words,
letters, etc. may be implemented in a `virtual machine' corresponding to
a high level programming language, which, in turn, is implemented in a
lower level machine language, and ultimately by quantum physical states
of electronic components, with several machine levels in between.  The
abstract  machines  at  all  levels  are  compound  objects,  composed
of many different kinds of entities, relations and processes.

     Moreover,  causal and functional relations may hold between the
high level abstract machine structures. (Changes in an abstract data-



                                         3

structure, such as a database of information about employees, can cause
changes in what gets printed on pay slips.) These data-structures may
have semantics in that they refer to individuals and their salaries,
etc. We have argued elsewhere that this can include semantics for the
machine (e.g. Sloman 94).

     In the case of human brains we do not know what the layers are.
Yet causal relations between abstract structures clearly occur when
a person's seeing something causes him to get angry, which in turn
may cause him to strike out. The fact that ultimately people, like
computers, are implemented in (ill-understood) physical mechanisms
is not inconsistent with this. Even physical phenomena are normally
explained well above the level of fundamental physics: most people
who learn how a car engine works are not taught about quantum
physics, but about carburettors, chokes, pistons, etc.

     Though a designer often knows a great deal about how a complex
system works, it may be impossible for others who merely observe the
system, to infer the internal processing. (Sometimes even the designer
does not understand all the internal interactions.) This means that
any philosophy of science that assumes that theories must be directly
or easily testable is ill-conceived: it will fail for complex information
processing systems, most of whose behaviour is internal and unobservable.
Moreover, even knowing how the system works may not provide
a basis for predicting particular behaviours if the behaviour depends
not only on the design and current circumstances but also on fine
details of enduring changes produced by a long previous history.

     When studying systems we have not designed we can, at best, hope
for a succession of theories accounting for more and more phenomena,
using increasingly powerful explanatory principles, tested in part by
implementing the theories in working designs and in part by relating
them to the ever growing body of knowledge in neuroscience. There may
never be a total ordering of merit among such theories, and the ordering
may change over time as new phenomena are discovered. Objections to our
approach are often based on a naive philosophy of science, or misplaced
`physics envy'. (For a broader view see Lakatos 70, chapter 2 of Sloman
78, and Bhaskar 78, 94).

     The design-based approach draws its inspiration from software
engineering and conceptual analysis in philosophy (see chapter 4 of
Sloman, 78). It construes AI as a methodology for exploring an abstract
space of possible requirements for functioning agents (niche space) and
the space of possible designs for such agents (design space) and the
mappings between them (Sloman 94, Sloman 95). Research strategies vary:
they may be top-down, bottom-up or middle-out. All are potentially
useful. This paper is largely top-down, but we do not exclude other
options, e.g. the use of genetic algorithms to create designs by
simulating evolutionary processes.

     Although it is often assumed that AI is concerned only with
algorithms (e.g., Searle 80, Penrose 89), architectures are more
important. We need to understand global designs for complete systems,
including their functional decomposition into coexisting interacting
sub-systems. Early work, still exploring general principles, need not
make any commitment to the implementation details of mechanisms; for
example, we take a neutral stance towards symbolic or connectionist
engines. We start with `broad but shallow' (Bates et al. 91)
architectures that combine many sorts of capabilities (such as
perception, planning, goal management, and action). Each capability is
initially


                                         4

implemented in a simplified fashion. Subsequent work gradually refines
and deepens the implementations.

     We claim that architecture dominates mechanism (Sloman, 93b),
i.e. global design normally determines global capabilities to a greater
extent than implementation details. Of course, we must ultimately
link designs to neural details and will profit from the `bottom up'
studies of such details, which impose constraints on high level designs.
Most of the constraints seem to be quite weak. Exceptions are the
high level effects of drugs, which we have not taken into account.

     We do not assume congruity between the design decisions `taken'
by evolution under environmental and competitive pressures and those
taken by a designer when moving from initial requirements (what the
system should do) to prototype design (how the system will do it).
Rather we merely claim that the design-based methodology is a source
of potential explanatory theories. Such theories will be improved under
pressure of criticism, either because of things they fail to explain, or
because they explain too much (e.g., capabilities people don't have),
or because the designs could not have evolved naturally, or could not
be implemented in brains.

     Even an oversimplified or incorrect theory that yields a workable
design can help our exploration of design space. Comparing it with
other more `realistic' theories aids our understanding of the latter, for
we don't really understand any system if we don't know how changing
it would produce different capabilities.

     Designs satisfying the same information processing and control
requirements may possess common design features, whether produced by
natural selection or human engineering, just as birds and aeroplanes are
both constrained by principles of aerodynamics. Over time the
design-based approach may gradually approximate natural `designs'. This
could happen by increasingly taking account of empirical constraints and
iterating the development cycle to deepen requirements and extend
designs. Such designs can also be tested empirically and compared in
more and more detail with their natural counterparts. The total research
community is effectively engaged in a parallel cooperative search.(*2)

     To summarise: (a) An architecture has causal powers that determine
the capabilities of an agent and explain its ability to `fit' into a
part of `niche' space; and (b) the design-based approach generates
candidate architectures that may correspond to naturally occurring high
level causal structures implemented upon neural substrates. These
candidates can guide empirical investigations to check such claims.

  ___________________________________
 *2Disparate research efforts are already developing architectures that
share a subset of design features given similar requirements. The
design of autonomous agent architectures grows apace. For example,
Firby's RAP (Firby, 87; Hanks & Firby, 90), the Oz Project (Loyall &
Bates, 91; Reilly, 93), Hayes-Roth's intelligent control systems
(Hayes-Roth, 91a, 91b, 93a & 93b), the Heuristic Control Virtual Machine
(Fehling et al., 89), Georgeff's PRS and Beaudoin's NML1 all share
significant design features (for a review see (Wright, 94) and
(Wooldridge & Jennings, 95)). However, this phase of agent design
may be overturned by revolutionary developments of ideas and techniques.
For example, (Brooks & Stein, 93) claim that increased parallelism and
the building of situated agents bottom-up will generate such a change.

                                         5

2.2 A motive-processing architecture

We now sketch an architecture(*3) that is partly similar to Georgeff's
Procedural Reasoning System (Georgeff & Ingrand, 89; Rao & Georgeff, 91;
Rao & Georgeff, 92), but allows a richer mental ontology, including
asynchronous goal generation, more coexisting concurrent sub-
mechanisms, a richer set of representations relating to motivators, an
attention filtering mechanism and meta-management processes. (Our ideas
on all this are still evolving.)

     A full account of the proposed architecture would be too long for
this paper, so we focus mainly on the processing of motivators.
`Motivator' is used to refer to a subclass of information structures
with dispositional powers to determine action (both internal and
external). This subsumes desires, goals, intentions and wishes. The
precise definitions of these structures and their powers can be given
only in terms of the architecture, which is roughly sketched in
Figure 1: an impressionistic diagram. For more details see (Beaudoin
94). Within this architecture, motivators can be generated or
re-activated asynchronously as a result of internal or external
events, and can generate processes of varying complexity, including
evaluation, prioritisation, selection, planning, plan execution, plan
suspension, and many more. Some of the processes that emerge from such
interactions we call `perturbances', and are described below.

     The large shaded area represents `automatic' processes (associative
memory, low level sensory analysis, low level motor control processes,
innate and trained reflexes) all implemented in highly parallel
dedicated (but trainable) `hardware'. We assume that such processes
include mechanisms shared with many other animals. The larger unshaded
area above that represent `management' processes involved in (among
other things) deciding whether new motivators should be adopted or not,
assessing their relative importance and urgency, deciding how to achieve
them, working out whether they are in conflict, deciding whether to
abandon them, reasoning about new information, formulating questions
about puzzling information, and so on. (All these processes can be
implemented at least approximately using AI techniques.)

     The management processes, but not the low level processes, can
create, consider and evaluate explicit (representations of) options
before selecting between them, for deliberation, planning and
problem-solving. This requires the ability to create temporary
complex information structures, often with complex syntactic forms,
often

  ___________________________________
 *3There are are at least two uses of the word `architecture'; one
referring to an abstraction or design that is common to many instances of
the architecture; and the other to concrete instances of such designs.
We use the former sense, in which an architecture is a collection of
features common to a class of entities. Each instance of an architecture
is composed of coexisting, interacting substructures with various
capabilities and functional roles. A substructure may also have an
architecture. The architecture of a complex system can explain how its
capabilities and behaviour arise out of the capabilities, behaviour,
relationships and interactions of the components. An architecture can
be specified at different levels of detail, e.g. at a high level of
abstraction the architecture of a house will not include the occurrence of
particular bricks, whereas a more detailed architectural specification would.

                                         6

FIGURE 1: Towards an Intelligent Agent Architecture

 [Showing sensors, effectors, a `low-level' sub-architecture in which
  there's a lot of automatic, pre-attentive processing, and a
  `higher-level' sub-architecture in which resource-limited management,
  and meta-management processes occur, protected by an attention
  filter.]

representing things that are not present to the senses (e.g. future
possible actions) and to switch attention between the structures.  We
suspect that most other animals do not share this capability with
humans: their architectures are not sufficiently rich.  There are both
empirical and design arguments supporting the claim that despite
parallelism in the brain such high level cognitive processes are
resource-limited: not all potentially useful management tasks can be
performed concurrently. So not all new motives, thoughts, problems, can
be considered simultaneously. This `processing-limit' leads to a
requirement for some type of filtering of `attention-distractors', as
explained below.

     The architecture has the following components (among others),
which coexist and operate concurrently. Many of these components
require a depth and complexity that we cannot describe here.

o Perceptual mechanisms. These are extremely complex systems, which
detect potentially relevant sensory episodes and analyse and interpret
them in terms of states and processes in the environment, creating or
modifying internal representations. A perceptual control mechanism
directs sensing operations. (Figure 1 oversimplifies drastically.)

o Database of `beliefs'. Information derived from perceptual
representations, internal monitoring and reasoning processes is stored
in a `world model', which acts as a store of information. This will
include both specific and general information, including a generic
ontology for objects, processes, actions, etc. It need not look anything
like current computer databases, for instance if implemented in a neural
net. Planning may use temporary `what-if' extensions to this store.

o A changing collection of motivators. A motivator is a

                                         7

semantically rich information structure that tends to produce, modify
or select between actions. It typically expresses a motivational attitude
(`make false', `keep true', etc.) towards a possible state of affairs
(`short of food', `warm', `in danger', etc.), which may be expressed
in propositional or non-propositional from. Motivators have various
associated information items, including urgency, importance and an
insistence value (Sloman, 87).(*4)

     A new motivator's insistence level determines its ability to
penetrate a (variable threshold) filter in order to be considered by
management processes.  Importance helps to determine whether it is
adopted as something to be achieved, if it is considered. In order not
to divert scarce resources, mechanisms assigning insistence values must
work using simple `heuristic' measures of importance and urgency.
Computing accurate measures of urgency and importance could be too slow
and computationally expensive, possibly diverting management processes
which the  insistence  mechanism  is  `designed'  to  protect.
However, insistence measures based on fallible heuristics can sometimes
cause `bad' decisions about what should and should not divert attention.

o Pre-attentive and attentive motive generactivators (Beaudoin 94).
These express agent `concerns' (Frijda 86; Moffat & Frijda, 95). They
operate asynchronously in parallel, triggered by internal and external
events. They generate and activate or reactivate motivators, and set or
reset their insistence level. E.g. the concern to maintain fluid levels
may activate a drink seeking motivator. A simple type of generactivator
could scour the `world model' for its `firing' conditions, and when they
are met a motivator is constructed and its insistence level set. Other
generactivators may be built into the physiological control system or
into perceptual mechanisms. Some may be very abstract and general, e.g.
reacting to states where another agent is in difficulty and creating a
desire to help. Some are innate, many are learnt and culturally
determined.

o Variable threshold attention filter.
An attention filter protects management processes by allowing only items
with insistence values `higher' than the current filter threshold to
divert management processes. When first learning to drive, many find it
difficult to hold a conversation simultaneously, as all high level
processes are required for driving and the filter threshold is set high.
However, attention can still be diverted by, say, the passenger
screaming (loud noises can trigger high insistence levels). Later, when
the driver is an expert, lower level mechanisms derived from earlier
management processes control most of the driving. This reduces the
management load, allowing a lower filter threshold and easier diversion
of attention. Filtering is content sensitive, with different thresholds
for different contents (Beaudoin, 94): A baby's cry can divert attention
even when other loud noises do not. Motivators that fail to surface may
remain available, so as to take advantage later of a lower filter
threshold, or they may die unless continually reactivated by the
relevant generactivators. Motivators survive until they are satisfied or
decay.

o Motive management.
Once a motivator has `surfaced' it can cause many diverse and complex
processes, including: assessing (evaluating its importance, urgency,
costs and benefits etc.), deciding (whether to adopt the motive, i.e.
form an intention), scheduling (when and under which conditions to act),
  ___________________________________
  *4 There  are  other  motivator  components  not  detailed  here;  see
(Beaudoin 94, Sloman & Poli 95).

                                         8

expansion (how to do it, i.e.  planning), prediction (projecting the
effects of hypothetical decisions), detecting motive conflicts,
detecting opportunities(*5), abandoning a motive and changing filter
thresholds. Information about current motivators (including intention
structures discussed below) is stored in a `motivator database'.  Only a
limited amount of parallelism is available for management processes.

o Plans  and  other  `databases'.
The system will have many short term and long term memories containing
information about current, future, or possible activities.  In
particular, certain goals require plans, and some re-usable plans will
be stored as well as information about how to create new plans. Other
information stores will include collections of particular skills, e.g.
linguistic skills, mathematical skills, skills relating to social
activities, games, one's job, etc.  Some of this will be stored in an
opaque form among the pre-attentive mechanisms. Some will be accessible
to management processes. Some will be innate, others learnt, some fixed
and others modifiable.

o Meta-management.
A meta-management process is any goal-directed process whose goal
refers either to a management or to a meta-management process. Deciding
whether to decide whether to adopt a goal, deciding which management
process to run now, and deciding if too much motive-swapping is
occurring, are all examples of meta-management processes, where motive
management itself is the object of control. Meta-management requires
some degree of ability to monitor and change the management processes.
Conflicts can lead to `loss of self control'. Again, resources are
limited.

o Plan execution and effectors.
Selected motivators are intentions. Executing them may occur with or
without planning, with or without high level management, with or without
monitoring. External actions are dispatched to an effector driver that
controls agent actions within the environment. Internal actions may
produce a succession of management states.

o  Self-monitoring  mechanisms.
A variety of types of self- monitoring are required.  Meta-management
monitors include those that can detect global states of the management
processes,  such as noticing that new motivators are surfacing faster
than they can be processed. This could lead to a raised filter
threshold. Other states worth detecting include repeatedly considering
the same goals or problems without making progress in solving them
(described as `maundering' in Beaudoin 94). A concept-learning mechanism
would be required for discovering useful new ways of describing internal
states. Humans can detect  inconsistencies  between  internal
management  tendencies  and personal ideals.

o Pleasure  and  pain  mechanisms.
Pleasure and pain have not been analysed adequately yet. They seem to
involve phylogenetically old structures in the nervous system that are
deeply implicated in mechanisms for both learning and online control:
i.e. whether current activities should be maintained or terminated.
Some people doubt that an information-processing architecture can fully
account for such subjective states. For now we assume that there are
mechanisms producing some motivational control states that are
pleasurable in the sense of involving a disposition to preserve or
extend some current state  or  activity,  and  some  that  are  painful,
involving  dispositions to terminate or reduce some state or process.

  ___________________________________
  *5 See (Pryor & Collins, 92).



                                         9

Some of the control states in the architecture may have a positive or
negative valency that arises out of genetically programmed drives (e.g.,
seeking after novelty, urge to procreate and form attachments) and
states of body arousal. Others involve learnt evaluations. For pain and
pleasure to be experienced requires self-monitoring mechanisms that
detect these `preserve/terminate' control states. The mechanisms may be
linked in that termination or reduction of pleasure inducing states
functions as a pain inducing state and vice versa. In some cases these
links will need to be built up through learnt associations. In others
they may be `hard-wired' in the architecture.

o Global control mechanisms.
An agent sometimes needs to modulate global features of its processing,
for instance speeding everything up in times of extreme danger, slowing
things down when losing energy too fast, generally being cautious when
the environment is unfriendly, not wasting time on caution when the
environment is generally friendly. Other more subtle global changes may
be required when the social context changes, for instance when an
individual of higher status is present. These global changes of state
seem to be related to the colloquial concept of `mood'. In humans it
seems that some of these global mood states are implemented in part at
the chemical level (as shown by effects of drugs and hormones). Some
control mechanisms may be `global' only relative to a subset of a
system: e.g. global changes in the ease with which unsuccessful attempts
are abandoned.

     We acknowledge that this design sketch is speculative, vague and
subject to revision in the light of implementation problems or empirical
evidence. Detailed designs may vary, e.g. some using rule-based systems,
others neural nets. The components may exist within a virtual (abstract)
machine whose components and processes do not correlate in any simple
way with physical structures and processes.

     A small subset of the architecture has been implemented (Wright,
94) and tested in a simulated domain, using very simple management
processes. A more elaborate implementation is in progress, using a
toolkit developed at Birmingham (Sloman & Poli 95).

     The architecture is `broad' in that it combines many different
capabilities. It is `shallow' in that the components are not themselves
specified in any great depth.  For testing purposes simple
implementations are used at first.  Much of the specification is still
provisional and speculative, in that work on implementation may reveal
serious problems. It is also speculative in that empirical checking has
not yet been attempted (and may be very difficult.) Nevertheless we
think the architecture already has explanatory power.



2.3      Varieties of control states


A mind can be viewed as a control system with a rich collection of
control states (Sloman 93b), involving dispositions to respond to
internal or external conditions with internal or external actions. Some
control states are implemented in high level abstract machines, others
in various sorts of neural states, or in states of chemicals in the
blood or nervous system. The described architecture provides a framework
within which many control states can coexist and interact.

     Examples of control states referred to in folk psychology are beliefs,


                                        10

images, suppositions, desires, preferences, intentions, moods, learnt
associations, innate or trained reflexes, personality traits, and emotional
states.  The dispositions may be of a high order (i.e.  dispositions to
invoke dispositions to invoke dispositions....(Ryle 49).)

     Every architecture supports a family of concepts describing its
states and processes. Exactly which control states are possible depends
on the architecture. A leaf's movements may speed up or slow down, but
it cannot be described as `braking' because it lacks the architecture
required for self-modification of speed, namely one sub-component which
acts on others to slow them down.

     The architectural presuppositions of ordinary mental terms are far
more deep and difficult to analyse. By defining states in terms of an
architecture that supports them we can offer a rational reconstruction
of many ordinary mental concepts, just as theories of the architecture
of matter rationalised concepts of physical and chemical stuff (e.g.,
`iron', `carbon', `water', etc.). Folk psychology concepts may implicitly
(pre-theoretically) refer to mechanisms of the general sort we describe,
even though they contain contradictions and confusions. We use them
only as first approximations. Later we hope to offer something more
systematic and analogous to the periodic table defining chemical elements.

     Every control state has structure, aetiology, powers,
transformation capabilities, liabilities, and in some cases semantics.
These ideas include analogues of the linguistic notions of syntax,
semantics, pragmatics, and inference (Sloman, 94). For example, a
motivator may have a complex internal structure (syntax), a content
(based on that structure) referring to certain states of affairs
(semantics), a functional role, i.e. dispositional powers to determine
internal and external actions (pragmatics). It may also enter into
processes that derive new motivators or plans (inference), it may be
brought about or triggered in various ways (aetiology), and may be
modified, suppressed or terminated by other processes (liabilities).
Some control states are short-lived (e.g., a motivator which is
immediately rejected, or whose goal is quickly achieved.) Others endure.

     A control state may exist but not express its causal powers, or may
express its causal powers but not determine action. Observed behaviour
will generally fail to indicate the full richness of the underlying
control states, especially the dormant states.

     Certain high level, long-term (motivational) states (such as
selfishness and other personality traits) are difficult to change,  are
modified only very slowly by learning and possess pervasive causal
powers corresponding to their abstractness and general control
applicability. Low-level, short-term states, such as a desire to scratch
an itch or to repay a favour, are easier to change and have more direct
causal powers corresponding to their specificity and narrower control
applicability.

     Some control states will gradually change their status over time,
via a process we call circulation in which control states move around
the system. Useful control states `percolate' up the hierarchy, gaining
in abstractness and resistance to change, and increasing their field of
influence.  Defunct long-term control states may gradually lose influence
through lack of use, leaving only a few relatively specific active
instances. An example may be standards and principles from a culture
one has left.

     Control states may be qualitatively transformed during circulation,

                                        11

for instance acquiring more general conditions of applicability. Higher
level general attitudes such as generosity of spirit, may also spawn
derivative specialised control states such as favouring a certain
political party _ another aspect of circulation.  Internal connections
between control states will set up suppressive or supportive
relationships, dependencies, mutual dependencies and, occasionally,
dead-locks.

     The net effect of all this is a process of `diffusion' in which the
effects of a major motivator are gradually distributed in myriad enduring
control sub-states, i.e. in motive generators, plan schemata,
preferences, and predictive strategies. In some cases the effects will
be irreversibly embedded in a host of reflexes and automatic responses.
(This is loosely analogous to the process of compiling a high level
language.)

     The totality of control states is a dynamic structure with complex
internal relations and many levels of control. High level control states
amenable to some degree of self-monitoring are among the requirements
for any architecture underlying human-like capabilities. Where there is
appropriate self-monitoring (described below) the system may also
acquire self-knowledge that triggers negative evaluations and new
high-level motivators attempting to change some aspects of the system
itself, whether previously learnt cognitive reflexes or high level
attitudes.

     A full specification of the architecture is work for the future.
Nevertheless, we can begin to use it schematically to explain certain
aspects of human mental functioning by mapping familiar experiences and
processes into control states and processes that could occur in this
sort of architecture; for instance, affectional bonds and `perturbant'
emotional states.


3      Architecture  as  explanatory  ground

In this section we apply the architecture to a concrete emotional
phenomenon: grief at the loss of a loved one. This is not a
comprehensive `theory of grief' but an application of a `broad but
shallow' architecture to the understanding of a complex cognitive
phenomenon. It will be seen that a complete architecture can account
better for the diversity of internal and external behaviour that can
occur during grief than an explanation focusing only on some emotional
mechanism.



3.1      Personal reports on grief


The following quotations (a) to (p) are based on extracts from a
first-hand account of grief, edited to disguise the origin.  After each
item we make some preliminary comments in italics, relating it to the
architecture. Later we expand on these comments.


(a) When the person finally passes on, the hurt is like no other.
       ... Now the memories of the good times seem to be like a film
       playing in my head.

      {This is one of many examples of partial loss of control of thought
       processes in emotional states: thoughts, motives and memories
       relating to the object of the emotion intrude and may even dominate
                                        12

       thought processes, making it hard to attend to other matters,
       even those judged to be urgent and important.}

(b) XXX called us the day after his friend died suddenly. He was
       broke, alone, grieving and gravely ill, staying at the hospice
       where he'd spent the last month by his friend's bedside. I flew
       to YYY and brought him home, where he spent the next ten
       weeks in hospital. He was so ill that it was hard even for me - a
       medically sophisticated person - to comprehend and accept.

      {New facts may not easily fit into one's belief system. This is
       linked to the pain they cause: not physical pain but mental pain,
       a major phenomenon to be explained.}

(c) I started grieving the day I received the phone call, continued
       grieving the day I met him in the hospice in YYY, and all the
       time I sat by his bedside back in ZZZ. It tore me apart to see
       what this disease had done to him: : :

      {Grief can be both extended and highly disruptive. Notice that
       `tore me apart' does not describe physical or physiological
       processes, but in a highly metaphorical way describes mental
       pro-cesses. Unpacking that sort of metaphor is part of the
       job of a deep theory of emotions.}

(d) At least, that's all I wished for silently over and over again as I
       sat next to him in the hospital.

      {Powerful new motivators sometimes cause futile behaviour.}

(e) When he died, I was initially in shock.

      {Shock can be physical or mental. We can't tell which was referred
       to here but it could easily have been both. One of the things to be
       explained is how mental events, e.g. learning about the death of
       a loved one, can produce profound physical effects. But we are
       primarily concerned with mental effects.}

(f ) And then there are details like writing obits, funeral arrangements,
       meeting his family, etc., which keep you busy. And then the grief
       resumes.

      {The ability of grief to control processing is a disposition in the
       sense of Ryle (49). (Dispositions and capabilities can exist for a
       long time without being manifested because their `triggering'
       conditions do not occur, like the fragility of a wine glass, or
       countervailing processes prevent their expression, like a dam wall
       preventing a potential flood.) Grief involves dispositions that
       may be temporarily ineffective because urgent and important tasks
       manage to hold attention. But during that time the disposition
       remains and when there's a chance it regains control. From this
       point of view it is misleading to say `the grief resumes'. It was
       there all along, though its manifestations were temporarily absent.}

(g) It has been two-phased for me. This summer I kept confronting
       the unreality of it all. XXX, dead? I was wracked with insomnia.
       Every night as I'd try to go to bed, indeed, during much of the
       day too, I would replay the details of the previous three months
       over and over and over again.

(h) Each recollection was full of almost indescribable pain, but it was
       also fresh with his presence, something I cherished and which I'd

                                        13

       missed daily for almost four years before. I wish I'd had some
       `good times' to replay too, but they were from an earlier time, ...
       and they were crowded out by the intensity of the recent months.

      {This helps to bring out some of the complexity of human emotional
       states: mixtures of different states are not uncommon. Several
       different dispositions can be `fighting' for control and the
       balance may shift from time to time. Not long ago, in a BBC
       radio interview, the captain of a women's yacht in a round the
       world race described her emotional state on arriving at the final
       port. It was an enormously complex mixture of: pride in achievement,
       sadness that it was all over, joy at the prospect of seeing
       loved ones again, delight at the prospect of eating (rations had
       been exhausted two days earlier), regret that they had not won
       the race, happy memories of teamwork and obstacles overcome,
       sadness that the team would now be parting, and so on.}

(i) I managed to keep up a bit of a social life during this summer.

      {In a state of grief, interactions that would normally be taken for
       granted and enjoyed may be difficult.}

(j) My overall mood was somber, but I was at least willing to be
       distracted by friends: : :

      {Sometimes when self control of thoughts is hard, external help is
       effective. A mood is a type of global state, which need not have a
       semantic focus, unlike emotions. Moods also need to be explained
       by a theory of the architecture of a mind.}

(k) I became more and more of a hermit. Things lost their savour
       for me, and I withdrew.

      {Some of the high level control states, which we may think of as
       forming the personality, can be profoundly changed by grief. This
       may affect a wide range of preferences, choices, strategies, plans,
       and behaviour.}

(l) Grief isn't something you can show for too long. People are un-
       comfortable with it. They will indulge you only for so long, so
       you just hold it inside, slog along and try to get on with life.

      {Besides the control problems which relate to tasks and goals that
       form part of normal life, the observation that grief has
       undesirable social consequences can generate a new second order
       control problem - namely, not allowing the grief to be shown or
       to intrude in social interactions. Many emotions generate second-
       order motivations relating to the control of those emotional states
       themselves.}

(m) The holidays and the new year are a natural marker, and they've
       kept me busy and distracted me.

      {Another example of external help with the control problem.}

(n)    I try to reintegrate myself with my social circle, and start seeing
       friends again more regularly.  But I'm worried; I don't want to
       let go of the grief. Sometimes I think it's all I have left of XXX.

      {Motivation in relation to the control of the emotional state may
       be very mixed. The griever who manages to control the grief and
       get on with life may also suffer feelings of guilt or regret because
       another motivator involving one's duty to the deceased seems to
       be violated,  or because of the feeling that overcoming the grief
       would itself be a sort of loss of contact with the deceased.}

                                        14

(o)    I don't want to enter his bedroom one day with indifference, and
       wonder how we might use the space. I don't want to stop crying
       every day when reminded of another piece of our time together.
       Well, I do, eventually, and I know I will, but I am not comfortable
       with this yet.

      {Another example of mixed and conflicting second order
       motivation relating to the state of grief.}

(p)    This was a gruelling, soul-grinding and exhausting year.  It has
       been the worst year of my life.

      {Emotional states normally involve evaluations. Powerful emotions
       often arise out of `intense' evaluations. The emotional states
       themselves can be evaluated and contribute to the judgement
       that something bad, or something good, is happening.}


     Those who have grieved or had close contact with a griever may
empathise with these extracts. Others will also understand, for these
are pervasive phenomena and play a major role in many works of art.
But we need to get beyond empathy and folk psychology to understand
the architecture underlying grieving and other affective states. Our
proposed architecture provides a provisional first draft explanation of
certain characteristic cognitive features of mourning in terms of causal
relations between underlying information processing mechanisms.

     The following are among the surface phenomena of grieving,
illustrated by the above extracts:


    1. The continual and repeated interruption of attention by memories
       or thoughts relating to the friend's illness and death; i.e.
       loss of `normal' control of thought processes (explained below).
       See [a, d, g, h].

    2. The difficulty of accepting the fact of the friend's illness and
       death. See [b, e, g].

    3. The disruptive effect on normal, day-to-day functioning. See [c,
       e, g, k, p].

    4. Periods of relative normality when grief is `backgrounded', some-
       times because external factors help one regain `normal' control.
       See [f, i, j, m].

    5. Attempts to `fight' the grief. [g: `try to go to bed', l: `hold it
       inside, slog along and try to get on with life'].

    6. Second order motivators, some of them involving evaluation of
       the grieving state as good or bad, including, in some cases,
       wishing the grief to continue. See [n, o].

    7. The subjective `pain' experienced by the mourner. There may
       be mental pain as well as bodily disturbances. See [a, h, p].

    8. Crying. See [o].


     These are not all the possible symptoms of long-term grief and
neither are they unique to grief: excited anticipation of a long awaited
event could also disrupt normal day-to-day functioning. Anger can also
be `backgrounded' when other demands control one's attention. Guilt
feelings, or an undesirable infatuation may also be fought against.


                                        15 
     Many theories of emotion concentrate either on the neural
substrate, external behaviour or externally observable changes (facial
ex- pression, posture, muscular tension, sweating, etc.), i.e.
evolutionarily old mechanisms shared with other animals. We are
deliberately ignoring most of these, indeed regarding them as only
marginally relevant, since, in principle, the mental phenomena that we
are concerned with could occur without these other accompaniments, for
instance, in beings from another planet whose mental functioning and
social life were much like ours despite considerable bodily differences
(see Sloman 92).

     We do not wish to argue over whether these phenomena are or are not
part of the definition of the word `emotion'. Many words of folk
psychology are notoriously ill-defined (Read & Sloman, 93; Kagan, 78),
both in colloquial use, and in scientific contexts where different
theorists offer different definitions. So instead of arguing over
definitions we merely identify certain types of familiar phenomena and
then ask what sorts of mechanisms might explain them. Since we are
interested in information processing explanations of information
processing phenomena we are not concerned that there are no behavioural
or physiological definitions of the phenomena: for example, there are no
behavioural or physical definitions of many of the states and processes
in information systems that are of interest to software engineers. They
are rightly not concerned that their work does not conform to narrow
(and often misguided) criteria of what constitutes `science'.

     Our interest is in information processing theories of affective states
because  we  expect  they  will  be  both  theoretically  and  practically
enormously fruitful in the long run, even though most of the people
who should be most concerned,  such as therapists,  counsellors and
educationalists,  are usually unaware of them on account of current
training regimes.

     For those that remain uncomfortable with a functional analysis of
affective states the following distinction may be helpful: many mental
terms have, besides their physical basis, two non-physical aspects -
phenomenological (subjective feelings states) and psychological
(functional role) (Chalmers, 96).  For example, `pain' certainly denotes
an unpleasant feeling state,  but it also refers to a functional role of
a pain control signal that leads to the withdrawal or avoidance of an
aversive stimulus. In our discussion the `phenomenological problem' is
factored out and placed to one side.  Our emphasis is on what causal
mechanisms do, not what it is to be like these causal mechanisms.



3.2      Self-control and perturbance


A grieving person is partly `out of control'.  Explaining this requires
an analysis of what it is to be in control. The ordinary notion of `self-
control' is not a unitary concept admitting of a unique analysis. Like
many mental concepts it covers a variety of cases and further study is
required to investigate how many of them can be accommodated within
the design-based framework. In particular, not all agent architectures
can support a distinction between being in control and not being in
control of one's thought processes.  For instance it is not clear that a
rat ever has control of thought processes.  In that case it cannot lose
control.  If that is so, the sorts of processes we are discussing cannot
occur in a rat.

     What kind of system can have control of its thought processes? A


                                        16

partial answer is that the system must be able to have goals relating
to its own thought processes, and it has control when everything that
occurs in it is consistent with all the currently adopted management
and meta-management goals. This does not imply that everything that
happens is generated by those goals, for that would rule out intrusions,
such as feeling hungry, or a new desire to help someone in trouble.
These can arise without contradicting one's view of what one should
be like.

     Our partial answer needs to be expanded in various ways. One is
to allow that there need not be only one coherent global set of goals,
preferences, etc. since some people seem to change personality from
one context to another, like the kind father who is an aggressive car
driver. The architecture might allow a number of different sets of
mutually consistent high level dispositions that co-exist, though only
one set is active at a time (as sketched in Ch. 10 of Sloman 78).

     Detection of incongruent states requires some sort of self-
monitoring of the global `picture' and an explicit evaluation of it as
fitting or not fitting the agent's ideals, long term objectives, or
previous decisions regarding (for example) what to think about, or which
desires are unacceptable. If a substantial amount of what is happening
at any time is inconsistent with the agent's dominant evaluations and
preferences, then the agent is, to that extent, partly out of control,
even if all the disturbances and disruptions are generated entirely
within the system, e.g. from lower level automatic, non-attentive,
processes, or reflexes in the management system. Addictions are an
extreme case.

     We use the term perturbant for a state in which partial loss of
control is due to the continual surfacing of postponed or rejected, or
unwanted, motivators (Beaudoin, 94), or possibly disruptive thoughts,
images, and the like (e.g., a catchy tune that won't `go away'). Such
disruption can interfere with the management of other, important goals.
This is the type of information processing state that the `attention
filter penetration' theory posits as characteristic of many emotional
states (Simon 67, Sloman & Croucher 81, Sloman 87, 92). It is what the
filter normally prevents.

     Perturbant states differ in several dimensions: duration; whether
the source is internal or external; semantic content (what is referred
to); type of disruption (it could be due to a goal, thought, or
recollection); effect on management processes; frequency of disruption;
positive or negative evaluation (compare grieving with being unable to
stop thinking about the victory one has recently won _ grieving and
gloating have much in common); how the state develops; whether and how
it decays; how easily it can be controlled, and so on.

     Perturbances (like `thrashing' in an overloaded computer operating
system) are side-effects of mechanisms whose major role is to do
something else (just as thrashing arises from the paging and swapping
mechanisms in the operating system). Perturbances arise from the
interactions between (a) resource-limited attentive processing, (b) a
subsystem that generates new candidates for such processing and (c) a
heuristic filter mechanism. These design elements arise from the
requirements for coping with complex and rapidly changing environments.
Perturbances do not arise because of some special perturbance generating
(or emotion generating) mechanism. Thus it is misguided to ask what the
function of perturbant states is or to postulate a perturbance
mechanism.
                                        17

     Our architecture was described above as concerned with processing
goals. However, other things should also be able to penetrate the filter
mechanism and divert management processes, such as items of factual
information about current or past events. Sometimes new information
generates motivators as a result of high level reasoning which interacts
with generactivators in the management system, for instance, discovering
that one's bank balance is very low. Also new factual information
may be required to interact with current plans and goals, for instance,
showing that a goal has been satisfied and is now redundant, or that a
short-cut is now available (Ch 6 of Sloman 78, Pryor & Collins 92). This
means that perturbant states can be produced not only by new motivators
but also episodic recollections, Simon's `cognitive associations'
(Simon, 67), or motivationally neutral thoughts.

     Can perturbant states be controlled? Self-control requires self-
knowledge. Control of motive management processes requires both
knowledge of what they are and motivators expressing what they should
be: a partly normative theory of the self, which can be used in
detecting and categorising internal states, just as knowledge and
desires are used in external perception and action. In humans there are
wide differences in degree and kind of self-knowledge, though mourners
usually know that they are mourning. People are aware of some aspects of
their own mental state which they can describe with more or less
precision and artistry.

     Monitoring of management processes may be based on detection
of such variables as the rate of surfacing of new motives, aspects of
their semantic content, their effects on processing, the current filter
threshold level, the rate of success of plans. Self-descriptions thus
produced may vary in scope and content, as in `My last goals were not
achieved', `I am usually calm', `I am happy now', `I am grieving over
my lost brother', `I feel depressed about life', `I am worried about a
job interview but looking forward to a hot bath'. Information sampled
from the stream of management processing can be stored to provide
data for the self-control mechanism.

     Such `internal perception', where the self-control mechanism is the
perceiver and motive processing is the environment, requires
non-intrusive or `transparent' monitoring that does not change the
processes observed, just as looking at a scene does not change the
scene. This is also a requirement for `software agent' architectures in
computing systems, where agents need to be able to observe and react to
actions of other agents in the system.  Full transparency is difficult,
or even impossible to achieve: architectures are always partly opaque.
Attempts to `trace' everything in a software system break down when the
tracing processes are traced. Self-knowledge is always incomplete, for
otherwise there would be an infinite regress, for instance, of beliefs
about beliefs about beliefs....

     The requirement for transparency of motive management processes may
be satisfied to different degrees by different designs (e.g., a neural
net monitoring a lower level neural net by `sampling' connections, or
procedures that can be interrogated about their functionality without
disrupting their operation (Rozas, 93), or blackboard architectures with
globally readable information spaces, or towers of self-referential
processors (Bawden, 88), and so forth). Exactly which forms of
transparency exist in which organisms is an empirical question. Which
forms are useful for which purposes is a design question.

     Access to information is not enough. The system must be able


                                        18

to produce adequate descriptions or categorisations.  So self-reflective
concepts are required for self-monitoring, including both concepts learnt
from the utterances of others (`Don't be angry', `Are you upset?') and
concepts induced internally via generic concept-learning mechanisms.
Thus both socially acquired descriptions and more or less idiosyncratic
categories will be used to refer to internal states.

     Besides self-monitoring, self-control requires selection of
remedies and their application. Like medical treatment self-control uses
a three-stage process of diagnosis (identifying the problem), selecting
strategies (selection of medication and prognosis), and applying them
within the system (treatment). There are numerous possible strategies,
with details differing between architectures. Some management strategies
will be socially inculcated while others are induced by generic learning
mechanisms from consequences of self-management decisions.

     Such a meta-management system will have, or develop, ways of
classifying internal states and associating appropriate strategies with
them _ often different strategies in different contexts. For example,
raising the attention filter threshold to counter perturbance may be
useful when it is difficult to keep up with new goals, but could be
disastrous in situations where some highly urgent and important new
information could turn up.

     Some control strategies treat symptoms: for example, counting
imaginary sheep to counteract insomnia. The sheep-counting strategy
works by concentrating deliberative resources on a motivationally
neutral task that requires full attention. The cause of insomnia remains
but its ability to divert resources is diminished by a rival task.
(This often fails.)  Another case of treating symptoms is turning to
drink in order to dull painful thoughts and emotional responses: a
strategy which depends on close coupling between chemical processes and
high level control states.

     More powerful self-control strategies may be more difficult to
apply:  removing the cause of the problem (dismantling an attachment
structure (defined below) or abandoning an unfulfilled desire _ often
difficult or impossible), suppressing external symptoms while internal
turmoil continues (the stiff upper lip syndrome), diverting the system
via tasks and external contexts that cause the attention filter
threshold to be raised, undergoing explicit or implicit training (or
therapy) that alters some of the links in the system (e.g. disabling
some generactivators or changing them so that they assign lower
insistence levels). Some of these are temporary palliatives, whilst
others have long term effects. Some may lead to new re-integrated
personalities, while others leave potentially harmful tensions within
the control system.

     Self-control is always limited. The difficulty in controlling
perturbances may have different causes. (a) Self-control
mechanisms have limited causal powers (hence the tension between the
ease of representing what you want to become and the difficulty of
becoming what you have represented (Smith, 86)); (b) self-monitoring is
limited by architectural opacity; (c) the system may lack the concepts
required to categorise internal states and express appropriate remedial
strategies; or (d) adequate control strategies may not yet be available.

     Powers of self-control mechanisms can be extended by various kinds
of training and practice. Opacity can sometimes be overcome by extra
reasoning (after the event), like inferring the shape of an occluded

                                        19

object during visual perception. New meta-management strategies
can be learnt through trial and error, social influences, or possibly
therapy.

     Psychological evidence exists for self-modelling, reflection and
self-repair, e.g. (Kuhl & Kraska, 89). Selecting or creating control
strategies requires a decision mechanism that can synthesise different
kinds of information _ current state of motive management, environmental
context, current goals, theory of the self and so on _ and then decide
on a strategy. This ability will vary between individuals.



3.3 Attachment structures

A raised surface can leave an impression on human skin; similarly,
interaction with another person will leave an `impression' on mentality.
Before the advent of information processing architectures this metaphor
could not be unpacked.

     Bowlby's theory of attachment (Bowlby, 79 & 88) attempts to explain
how affectional bonds are created and the effects that occur when such
bonds are broken. Although criticised in recent times (particularly the
emphasis on maternal deprivation in childhood to explain subsequent
problems in adulthood; see (Smith & Cowie, 91), Ch.3) attachment theory
is still used to account for both childhood and adult mourning in
clinical psychology. We shall explore this theory within our proposed
architecture, showing how processes described above as percolation,
circulation and diffusion allow a distributed multicomponent `structure
of attachment' to an individual to develop and influence subsequent
processing. Being deeply entrenched at many levels within the control
hierarchy it manifests itself in multifarious ways when its object dies.

     The perceptual system and belief systems of an agent will include
information about other agents, including information about how to
recognize them and what behaviour to expect from them in various
situations. This may also include evaluations such as `X is a good
person' or `X is dependable'. Interaction with X will lead to creation
of motive generactivators expressing motivational attitudes towards X.
Over time, enduring control states pertaining to X will be generated
that interact with higher level attitudes and personality traits within
the hierarchy of dispositional control states.

     For example, various preferential mechanisms may be set up (`prefer
to be in the company of X'), which could function as motive comparators;
or unfocused and abstract wishes (`wish X is always happy and well');
also desires (`desire to holiday with X sometime soon' or `desire to
spend more time with X'), hopes (`hope X likes me', `hope X enjoys my
company', `hope that X will remain close') and aims (`maintain
friendship with X', `avoid arguments with X'). High level preferences
may generate lower level motive generators: for example, preferring to
be in the company of X could generate the aim to maintain the friendship
of X. In other words, a diverse collection of control states with
complex interrelations and dispositional powers will be created
alongside factual information collected through interactions with X.

     The evaluations, generactivators and motivators will be positive
towards some individuals, negative or neutral towards others, and with
varying degrees of strength, possibly involving the pleasure and pain
mechanisms. Depending on the particular combinations of evaluations


                                        20

and other attitudes towards an individual, the death of that individual
may cause grief or some other kind of emotional state, or no emotional
state. A pre-requisite for grief is strong positive evaluation, though
that is not sufficient, for the death of a person whom one admires
or respects greatly need not cause grief. Something more is required,
namely the sort of entanglement of personalities commonly labelled as
`love' (another highly ambiguous term).

     The kind of loving that potentially leads to grief, which we are
calling `attachment', is a very complex mixture of states that develop
over time through mutual interaction. It will involve many dispositions,
including dispositions that produce pleasurable feelings in the company
of the person, displeasure when the person is absent or harmed, and so
on. Besides feelings, attachment structures can generate new motivators
relating to the person, e.g. when information is received about that
person's needs, successes, failures, suffering, etc. All these new
(dispositional) control states generated by the process of attachment
will, over time, integrate into the existing control network: the
process we have called `diffusion.'

     These control states involve many dispositions, including potential
influences on both pre-attentive and attentive processes. The former
include (a) a tendency for new motives to be generated pertaining to
X; (b) assigning relatively high insistence values to motives concerned
with X, particularly if there is a serious problem involving X that
needs urgent attention; (c) allowing the filtering mechanism to give
preferential surfacing conditions to X-related motives, as all things
relating to person X are deemed important (compare a mother and
her baby); and (d) new links between phenomena involving X and the
pain and pleasure mechanisms.

     Effects on attentive, management processes include: (e) new
dedicated decision procedures with regard to X (e.g., skewed importance,
urgency and cost-benefit computations that raise the priority of
X-related motives); (f) creation of unusually detailed (possibly
unrealistic) predictive models about X's behaviour and preferences; (g)
clusters of management procedures that manage X-related motives by
combining model-based information, current and new goals to form new
intentions; (g) a relatively high proportion of items in the goal
database concerned with long, medium and short-term intentions relating
to X, in various states, such as conditionally suspended, postponed,
ongoing etc.; (h) an unusually high proportion of intentions that are
long term mutual or joint plans predicated on the co-operation and
continued proximity of X; and possibly (i) new motive conflicts
pertaining to X, e.g. the combination of preferring to be in the company
of X, wishing that X is happy and believing that X wishes to be alone,
or loves another. Great novels and real human tragedies often depend on
such conflicts and the processes they generate.

     Meta-management procedures may be generated or altered during the
growth of attachment. For example, management tasks of the form `decide
whether to adopt motive M' may come to be be handled as soon as possible
if M pertains to X. Relatively more computational resources may come to
be allotted to any decision procedure concerned with X. A host of plan
libraries expressing the utility of certain actions for achieving goals
with regard to X will be formed, which facilitate planning relating to
X; and `chunks' of actions that appear to be efficacious when dealing
with X may be abnormally strongly reinforced and lead to stereotypical
and positively valenced patterns of interaction.



                                        21

     Summary: an `attachment structure' relating to an individual is a
highly distributed collection of information stores and active
components embedded in different parts of the architecture and linked to
many other potential control states. When an attachment structure
concerning individual X exists in an agent, almost any information about
X is likely to trigger some internal reaction. In particular,
information about good things or bad things happening to X may trigger
reactions whose strength and pervasiveness depends on how good or bad
they are. Death is a particularly bad event.

     In this paper we shall not attempt to describe the process of
detachment, in which the attachment structure is gradually dismembered
and possibly replaced by a new complex set of beliefs and motives
relating to X, consistent with X no longer being alive. This drawn-out
process is part of a self-control strategy for overcoming perturbance,
albeit a long-term strategy that attempts a design change to achieve its
ends. This process can be analysed into many sub-problems _ for example,
the structure of attachment would need to be inspected for the sources
of perturbance, blame assigned, a modification of the structure
selected, and repair work effected followed by some kind of verification
process to check whether the modification had resulted in an
improvement.

     These are all extremely sketchy ideas that need to be developed
in the light of a more detailed specification of the architecture and
its `learning' capabilities. Yet all the proposed control states are of a
type that we claim could be implemented (with difficulty) in a suitably
rich architecture based on AI mechanisms, possibly using a mixture of
neural nets and symbolic processes.



3.4 An architecturally grounded analysis of grief

We now return to the symptoms of grief and attempt an architecturally
grounded interpretation of the surface phenomena in terms of an
attachment structure in the griever towards the deceased.


       1. The continual and repeated interruption of attention by
       memories or thoughts relating to the friend's illness and
       death.


     We have already described (Section 3.2) how the architecture
permits perturbant states when heuristic mechanisms designed to prevent
disturbance of resource limited processes continually `let through'
motivators and thoughts that divert attention from highly valued
activities. Following bereavement, cyclic processes could occur,
involving, among other things: motives relating to the dead person,
generated by long term attachment structures, including desires for the
person to be alive, or present, or unharmed; wishing one had done things
that might have prevented the death; recalling that the person is dead;
rejection of the motives as therefore inappropriate or futile;
evaluating such rejection as undesirable; reminders of relevant
information concerning the person, such as might be important if the
rejected goals were being acted on. These and other interactions might
all reverberate throughout the system because of the deeply entrenched
information structures and the powerful triggering effect of news that
the worst possible harm has already happened to the person.
                                        22

     Some of these events may set off a stream of deliberative thought
(or meta management processes) attempting to re-orientate extant
desires, intentions and plans, to cope with the changed circumstances.
This process could also trigger the recall of associated memories in the
form of different sensory modalities (images, smells, sounds etc.), as
well as triggering a host of embedded generactivators waiting in the
wings.

     The structure of attachment explains why motives relating to X are
likely to disrupt attention. (a) X-related motives will be given high
insistence values because the relationship with X is strongly positively
valenced and X has suffered great harm. (b) Exception fields within the
filtering mechanism may provide preferential surfacing conditions for
X-related motives and thoughts. (c) Higher level, abstract control
states expressing attitudes or preferences towards X may influence lower
level motive generators not directly concerned with X, producing
`partially X-related' motives. (d) Meta-management control processes
ensure that motives and thoughts pertaining to X are always decided as
soon as possible, so that such motives tend to grab attentive resources
immediately. (e) Dedicated evaluation procedures rate X-related motives
preferentially, assigning skewed importance, urgency and cost-benefit
measures. (f) Predictive models, triggered by X-related motives, will
consume computational resources by attempting to reason about about X's
needs and possible reactions to things. (g) In a resource-limited
system, the proliferation of motives pertaining to X may `crowd out'
other motive generators.

     Besides internal processes that spontaneously occur following the
news of X's death, external reminders may trigger additional X-related
processes: e.g. driving past X's favourite restaurant or accidentally
finding an old photograph, or hearing X mentioned in a conversation.
In some environments such reminders will be frequent. Perceptual
schemata looking out for the `lost' individual may misidentify strangers
as X. The association of places, objects and events with memories of the
deceased may be powerful triggers for perturbant episodes, sustaining
the period of mourning and making recovery difficult without a change of
location.

     To summarise: If a structure of attachment to X exists then motives
and thoughts pertaining to X will surface and successfully compete
for attentive computational resources; news relating to X's death will
therefore have a strong tendency to generate perturbant states. The
agent's thought processes will be partly out of control.


       2. The difficulty of accepting the fact of the friend's illness
       and death.

     Updating many entries in a large database of information can take
time, including the time for restructuring and propagation. This is
one notion of the `difficulty' of accepting new information.

     Another factor is resistance to change. The agent has `affective'
grounds for wanting to believe that information about X's death is
false. This could include long term high commitment intentions
pertaining to X, involving mutual plans that have had resources expended
on them, which the agent does not wish to regard as wasted. Besides
uncomfortable evaluations, complete assimilation of the new information
may require extensive resource-consuming cognitive reorganisa- tion
because the attachment structure is distributed and interwoven

                                        23

with other control states. Humans often seem to reject information,
however reliable, if it requires extensive reorganisation of control states
and value systems. This may be part of a good engineering design for
intelligent agents in a mostly stable world.

     Finally, the agent may know from past experience that the
acceptance of such beliefs entails a long process of suffering and pain.
Holding out hope that the information may turn out to be false is a
management goal to delay the onset of this process.


       3. The disruptive effect on normal, day-to-day functioning.


     Perturbance involves disruption of the processes of motive
management, and day-to-day goal processing may be adversely affected by
management overload. It is difficult to plan a shopping trip or attend
to what others are saying when distracted by futile regrets or painful
thoughts and memories.

     Besides cognitive disturbance, bereavement can cause physiological
changes in the mourner, such as weight loss and excessive tiredness,
which will contribute to a lack of efficacy; however, this is not explained
by our architecture.


       4. Periods of relative normality when grief is `backgrounded',
       sometimes because external factors help one regain
       `normal' control.


     When the management system is involved in new important and urgent
tasks it sets the interrupt filter threshold so high that the conditions
discussed above no longer hold, like the soldier or football player who
is injured and yet feels no pain. When the external demands are removed,
the threshold drops, and processes relating to the bereavement regain
control.

     Another factor may be a general mood of depression that `colours'
motive processing during grief. A depressed mood is a global control
state that `scales-down' interaction with the environment. (We do not
have space for a full discussion of moods.)


       5. Attempts to `fight' the grief.

     How can the mourner `fight' the grief and `try' to get on with
life? `Fighting' here refers to a kind of mental striving or conscious
selfcontrol, which is not always easy. It requires some way of
suppressing perturbant states, which is often much harder than control
of emotional expression (external symptoms).

     When the bereaved is attempting to work yet thoughts are
continually drawn to the recent death, the self-control mechanism
described above may detect the perturbance and attempt to negate its
disruptive effects. Until detachment has been achieved, such
self-control is partial and transient: the mourning returns when
fragments of the attachment structure are next triggered, by external or
internal (possibly subconscious) processes.

     One form of self-control uses the artificial `deadening' of
cognitive activity by alcohol or anti-depressants. Chemicals can alter
the functioning of abstract machines through their effect on the
neurophysiological substrate. Although understandable, this strategy

                                        24

could exacerbate the problem (drink can make people maudlin) or possibly
slow down the process of detachment.

     People are sometimes exhorted to try intentional suppression of
perturbing thoughts, using internal imperatives: `don't think about
that', `ignore that', `put these thoughts out of mind' etc. This could
also flow from a meta-management process, spawned by a self-control
mechanism, which rejects new motives pertaining to the deceased.
Some people may have learnt how to raise their attention filter threshold
deliberately. In practice instructions to oneself often fail.

     Even if temporarily successful this may lead to a build up of
motives waiting to surface, since the cause of perturbance remains.
Sudden surfacing of these suppressed motives could produce breakdown of
control if there is a drop in the filter threshold due to low management
load. Thus a person experiencing grief might function normally at work
during the day (when high management load sets a high filter threshold)
only to break down at home later (when both load and threshold drop).

     Even at home one can try to absorb oneself in attention grabbing,
computationally expensive tasks. `And then there are details like
writing obits, funeral arrangements, meeting his family, etc., which
keep you busy. And then the grief resumes.' Arranging the funeral has to
be done and can divert attention for a while, whereas attempting to read
an interesting book fails.

     However, as the intensity of grief lessens through gradual
dismantling of the attachment structure, thoughts and motives relating
to X have lower insistence, allowing `normal' tasks with low importance
and urgency to hold attention and prevent perturbance, and permitting
enjoyment of activities such as listening to music, playing games,
reading books, or conversing with others.

     Another coping strategy is the formation of a new affectional bond
to replace the old one (`on the rebound') _ an option that is not
always available, especially to an older person who has lost a spouse.
The formation of such a bond might be a way to avoid the lengthy and
painful process of detaching the structure of attachment by finding
a new use for it. This involves replacing the original referent and
possibly other things, and will not be achieved easily because of the
distributed mechanisms and links that constitute attachment. This
might be connected with the phenomenon of `projection', where the
grieving person views the new person in terms of the old.

     Some of these strategies may be ineffective, or may have
undesirable side effects, including hindering the long term process of
detach- ment. The pressure to find quick fixes may come from the
culture, for example through the necessity to keep one's job. This could
cause harm if the only satisfactory strategy for achieving internal
reorganisation following death of a loved one is through the natural
process of grieving.

     Examples of strategies that might aid this process are acceptance
(as opposed to suppression), via a meta-level goal to interpret the
experience of grief positively, by understanding that grief is necessary
and worthwhile. A supportive social circle may be required for this
to work. The self-control of emotional expression (`hold it inside, slog
along and try to get on with life') becomes necessary when friends or
work colleagues are less prepared to make allowances. It is difficult to
control facial expression and general demeanour. People can usually
see through the attempt. Limitations on our ability to dissimulate may


                                        25

arise from requirements for successful social co-operation (Sloman 92).


       6. Second order motivators, some of them involving evaluation
       of the grieving state as good or bad, including, in
       some cases, wishing the grief to continue. See [o, q].


     Disruptive and painful processes can trigger a second order motive
to end the state. But the mourner quoted wishes to preserve his grief:
`I don't want to let go of the grief. Sometimes I think it's all I have
left of XXX.' And `I don't want to stop crying every day as I'm reminded
of another piece of our time together. Well, I do, eventually, and I
know I will, but I am not comfortable with this yet.' Why should the
mourner _ paradoxically _ wish the grief to continue? There are a number
of elements at work here: (a) the knowledge that the period of intense
grieving may be coming to an end, (b) the association between grieving
and the recollection of memories of the deceased, (c) a conflict of
meta-level motivation between wanting to stop grieving and not wanting
to.

     The architecture described can support such conflicting processes.
For example, detachment may be occurring concurrently with a
metamanagement process that ensures that the deceased is not forgotten,
but remembered with the appropriate sadness. The meta-management process
may have been constructed by a collection of high level control states
constituting a self-image; for example, the mourner may view himself as
somebody who loved the deceased very much and consequently should
experience the appropriate amount of grief and heartache. (Cultural
norms will affect this.)

     Second order effects are to be expected within the framework of the
architecture. The meta-management system includes self-monitoring
processes that allow high level motive generators to be triggered by the
detection of internal states that require some change in management
strategy. Some of these simply redirect attention and cause sensible
evaluating, reasoning, deciding, and planning to occur. Others generate
some new motives that are, for one reason or another, hard to achieve,
and some that are rejected yet go on being reactivated and interrupting
processing. Exactly how all this develops will vary from individual to
individual and within an individual from one situation to another.
Second order processes may be strongly influenced by a culture.


       7. The subjective `pain' experienced by the mourner. There
       may be mental pain as well as bodily disturbances.

     Why is grief a subjectively painful `soul-grinding' experience? Some
perturbant states are very pleasurable (such as excited anticipation);
consequently, a structure of attachment perturbing attentive processing
is not a sufficient condition for grief. The pain presumably comes via
the fact that the death violates so many of the motives and preferences
associated with the attachment structure. Further research is in
progress to explain the roles of pain, pleasure and evaluation in the
architecture.


       8. Crying. Can we provide a design-based account of the
       onset of crying? Why does wailing or howling occur in
       times of extreme emotional distress?


                                        26

     Infants cry when their desires are unsatisfied. This grabs the
attention of an adult who will then normally attend to the baby's needs.
For a baby in the helpless altricial stage crying is a basic,
genetically determined, plan. It is the only way to satisfy its needs
for food, warmth, milk etc. Later, crying is no longer necessary because
there is a repertoire of plans and the agent can act independently.

     Consider the following scenario. A loved one suddenly died a few
weeks ago and you are in mourning. You were thinking about going
shopping but your attention was disrupted by thoughts of the lost one. A
perturbant state is manifest. Your thoughts are out of control and you
cannot stop thinking about what you were going to do together, the
things you miss sharing with them, that you are lonely and without a
close friend, and so on. You stare at the wall and ruminate. In terms of
the architecture the structure of attachment is generating motives that
are surfacing through the attention filter to disrupt management
processes. These motives, pertaining to the dead person, are
unsatisfiable and therefore rejected. But their high insistence makes
them surface again, foiling any plans for regaining control. In this
situation, the basic plan of crying may be invoked because (a) no other
plans from the repertoire exist for the surfacing motives, (b) the
invocation conditions of the basic plan are situations where `nothing
can be done', i.e. identical to the altricial stage of development, (c)
the basic plan has worked in the past to satisfy desires in such
situations, and (d) it has general applicability, i.e. was used to
satisfy diverse and basic wants such as food, warmth, milk, and
proximity to adults. Crying is the plan of last resort, and can be
triggered by negatively valenced perturbant states. There may be other
`basic' plans, some concerned with internal processes only.

     This explains Sartre view of `emotions' as an attempt to
`magically' transform the world (Sartre, 48). From an infant's
standpoint, crying achieves things by magic. As children grow their
helplessness diminishes, along with the need to cry. (The picture
becomes complicated later on, when the possibility of emotional
deception is discovered _ faking crying to manipulate others.)

     Also, the notion of `basic plans' as control mechanisms of last
resort bears important similarities to Kraemer's cascade hypothesis
(Kraemer, 92), which states that control will `cascade' down to
`genetically programmed neurobiological adaptive behaviours' if the
organism is faced with `disasters' (problematic situations) that its
`acquired behaviours' cannot deal with. However, Kraemer's approach is
very differ- ent from ours, namely psychobiological as opposed to
cognitive, and leads to seemingly different answers (biogenic amine
system function as opposed to information processing). There is no space
for a full comparison here, but a synthesis should be possible. For
example, our notion of a basic plan makes no commitment to its
implementation details. The integration of `bottom-up' approaches with
`top-down' requirements-driven design work should yield fruitful, and
not necessarily contradictory, results.



3.5 Discussion

Using the postulated architecture, we have offered a partial and
provisional design-based interpretation of many aspects of human grief.
However, our theory is sketchy, incomplete and offered only as an
initial step towards a comprehensive theory of emotions informed by the

                                        27

exploration of agent architectures in which control mechanisms are
information based.



1 For each loved person, a structure of attachment develops, consisting
       of diverse distributed mechanisms and representations
       with varying powers of persistence and dispositional causal roles
       in determining behaviour. This is the affectional bond.

2 Removal of the referent renders the structure of attachment
       inappropriate for the control of behaviour.(*6) Nevertheless,
       triggered by the news of the death and reverberating
       associations, the attachment structure generates thoughts and
       motives that surface and divert attentive resources, producing
       negatively valenced perturbant states.

3 Perturbant states disrupt normal functioning in resource-limited
       management processes.

4 The futility of other plans may trigger regression to a basic plan
       of crying.

5 Various self-control strategies may be instigated to overcome the
       perturbant states; however, the phenomenology of grief suggests
       that the causal powers of self-control mechanisms are limited.

6 Detachment takes time due to the deep and diffuse embedding of
       the attachment structure in the architecture. Extensive cognitive
       reorganisation and re-learning is required before the generation
       of perturbant states ceases, or drops to a manageable level. How
       long it takes will depend on details of the case. Some grief lasts
       as long as the griever.


     Much work is still required, to deal with many difficulties and gaps
in the design and the interpretation we have based on it. Problematic
areas include mechanisms for: learning, pleasure and pain, self mon-
itoring, the hierarchy of dispositional control states, self-controlling
abilities, the kinds of global control indicated by mood changes, and
the processes which assemble and disassemble attachment structures,

     Terms such as `attention' and `conscious' have been used without
precise definitions. When fully specified the architecture will be used
as the basis for a host of new definitions of classes of mental states and
processes (like basing the descriptions of types of physical stuff on a
theory of the architecture of matter).

     Questions arise about the possibility of using the architecture to
explain other perturbant states such as distress at the ending of a
relationship, excited anticipation, sexual infatuation, obsessive love
of a child, various pathologies of motivation or attention such as
obsessivecompulsive disorder and attention deficit disorder. These are
all pos- sible directions for future work.

     It is hard to think about the multifarious states and processes that
can occur in such a complex paper design. A working implementation
can aid analytical thinking, by exposing consequences of the design.
An implementable scenario for investigating perturbance is outlined
in (Wright, 94), and further work is in progress. This has led us
  ___________________________________
 6* Compare Oatley's treatment of grief: `a whole repertoire of
sub-plans and knowledge becomes useless' (Oatley, 92).


                                        28

to extend the architecture, to overcome limitations of early versions
which assumed a fixed succession of processes to be applied to new
motivators. This proved unworkable (Beaudoin 94).

     It may be objected that the use of an architecture as explanatory
ground merely restates the obvious in a more complicated way,
particularly if it generates no new testable predictions. This expresses
a naive view of complex information processing systems. Prediction may
be impossible because some determinants of behaviour are inaccessible
internal information states.

     Our work can be classified as belonging to the `creative modelling'
phase of science (Bhaskar, 78 & 94), where competing models of
generative mechanisms of surface phenomena are explored. Until we have a
good `design-space' of broad and increasingly deep agent architectures
it will be difficult to move from hypothetical explanation to justified
selection between hypotheses. The research community operating as
parallel search in both empirical and theoretical directions will
ultimately select between competing theories, using a variety of
criteria including generality, simplicity, implementability,
evolvability and applicability to other animals. But the theories need
to be developed. Using an architecture as explanatory ground is a first
step.

     The interpretation of grief given here may be compared with other
design-based models of emotionality, which tend to reason about
emotional labels based on an operational semantics of emotion concepts
(for example, see (Dyer, 87), (Frijda & Swagerman, 87) and (Pfeifer,
92)). On our model such emotion concepts would arise from internal
perception of motive processing states, self-control mechanisms and
social interaction. Another point in favour of the architecturally
groun- ded interpretation is that it has greater explanatory power than
that of folk psychology. For example, we begin to give answers to the
following questions: What is grief ? - Grief is (often) an extended
process of cognitive reorganisation characterised by the occurrence of
negatively valenced perturbant states caused by an attachment structure
reacting to news of the death. What causes grief to endure? - Grief
persists because of the time required to disassemble a complex,
distributed and deep attachment structure. Why does grief consume the
mourner? - Attentive processing is resource-bound and becomes swamped by
highly insistent motives generated by a structure of attachment to a
highly valued individual; in addition, the requirements for re-learning
and detachment entail extensive rumination that can also generate
perturbant states. Why do we cry during grief ? - In processing
situations where strong but unsatisfiable motives surface, a time may
come when otherwise helpless management processes resort to a basic
plan. Crying is the plan of last resort. Why can't grief be overcome
easily? - Processes of self-control are limited by architectural
opacity, the lack of adequate categorisations of internal states, the
lack of good meta-management strategies, and the disruptive effects of
perturbances.

4 Concluding comments

We have sketched an architecture of a sort that might be useful for
an intelligent agent with multiple asynchronously generated goals in a
complex and changing environment. We have shown how perturbant
states can emerge in such an architecture and how a structure of

                                        29

attachment can generate ongoing perturbance after bereavement. This
extends some previous theories of emotions and draws attention to new
research problems, some of which require more detailed design
specifications and some more detailed empirical investigations of
phenomena involving grief and other perturbant states.

     Our architecturally grounded interpretation of human grief has been
provided within a design-based framework. We expect development of the
design to lead to more fine-grained analysis of well-known phenomena,
generating hard cases that will force further development of the theory.
Detailed implementations may reveal unexpected insights, along with
hidden flaws in the theory and also with opportun- ities to extend it.

     No strong claim is made that the interpretation is the theory;
currently, we are only exploring theoretical possibilities and
illustrating a new approach to the study of complex mental phenomena.

     We have extended our earlier (pre 1995) design, particularly in the
direction of self-monitoring and self-controlling abilities, and alluded
to the need for further extension, e.g. learning mechanisms. Sartre's
intuition that `emotions' are magical attempts to transform the world
has been architecturally grounded via the idea of a fall-back plan in
situations of helplessness. We have not yet said anything about links
with neural structures and processes or emotional mechanisms shared
with other animals.

     We must stress that whether the actual interpretation of grief
outlined here is correct in detail is of secondary importance. A
stronger claim can be made for the methodology that generated the
interpretation. In order fully to understand the complexity of human
behaviour we have to posit new ontologies at the information processing
level of description just as a designer specifies an architecture to
meet some collection of behavioural requirements. By exploring families
of related architectures and their strengths and weaknesses in relation
to various niches, we may be able eventually to explain not only current
human capabilities but also the evolution of human and non-human mental
architectures in a variety of organisms. The work will also give us new
insights into what to expect if and when we design autonomous artificial
agents, whose internal complexity will make detailed prediction of their
behaviour very difficult.

     That all this will be a long and difficult process, with continual
revision of ideas, is not in question.



     Acknowledgements

     This work was supported by the UK Joint Council Initiative and
the Renaissance Trust.

     Thanks to Christian Paterson, Chris Complin and past and present
members of the Cognition and Affect project at Birmingham. Additional
papers by the group can be found at the ftp site:

     ftp://ftp.cs.bham.ac.uk/pub/groups/cog_affect/0-INDEX.html

     and in Aaron Sloman's Web page

     http://www.cs.bham.ac.uk/"axs/cogaff.html

                                        30

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