The Fables of Lucy R.:
Association and Dissociation in Neural Networks
Dan Lloyd
Department of Philosophy
Program in Neuroscience
Trinity College
Hartford, CT 06106
According to Aristotle, "to be learning something is the
greatest of pleasures not only to the philosopher but also to the
rest of mankind," (Poetics 1448b). But even as he
affirms the unbounded human capacity for integrating new
experience with existing knowledge, he alludes to a significant
exception: "The sight of certain things gives us pain, but
we enjoy looking at the most exact images of them, whether the
forms of animals which we greatly despise or of corpses."
Our capacity for learning is happily engaged in viewing
representations of painful objects, but not, it seems, in viewing
the objects themselves. When an experience is intensely painful,
what then is a rational animal to do? We can neither disable our
learning process, nor erase its traces. In the face of intense
pain, horror, or terror, learning and remembrance cause no
pleasure but rather persistent psychological pain and disruption.
The memorious mind reverberates with trauma.
The traumatized mind responds in diverse ways to the recurrent
crises of reminiscence, responses which lead at the extreme to
the symptoms of various disorders. These reactions fall into two
broad camps, the associative and the dissociative. The first is
exemplified by some (but not all) of the symptoms of
post-traumatic stress disorder, in cases where even a trivial
element associated with the painful event becomes an evocative
cue for reliving the experience. In contrast, dissociation is
characterized by subjective distancing from the initial pain and
its remembrance, often with secondary effects. In dissociative
amnesia, for example, subjects fail to recall critical spans of
their lives, often seeming to obliterate the traumatic memory.
The erasure is only apparent; in diverse ways the trauma
continues to oppress even if it cannot be consciously recalled.
There are, or course, many (too many) occasions of trauma. That
diversity, and the diversity of responses in its aftermath, imply
that the causal mechanisms of traumatized cognition are manifold.
Understanding post-traumatic psychopathology is further
complicated by the compounded effects of multiple or repeated
trauma. With this complexity in mind, in this chapter I will
explore connectionism as a unifying framework for understanding
the traumatized mind. The first motive for this attempt is
already apparent. Trauma is an occasion for a kind of learning,
and connectionist models are most adept at simulating learning.
In addition, a connectionist model offers extraordinary
flexibility in representation. Arrays of neural processing units
afford subtlety and precision in simulating the contents of mind.
With learning, these representations change. "Traumatic
learning" can thus be modelled, and a network observed in
its initial responses, and then subjected to further simulated
trauma with further testing. In this way, a narrative of
traumatic experience and its diverse psychological manifestations
can be condensed, simplified, and examined. Even a simple network
allows many variations. For a first foray into the simulation of
psychogenic psychopathology, I followed a well-known case study,
using the concrete history and experienced symptoms of a patient
(and her therapist) as a guide for a network model. The case
study is exemplary of the 90s -- the 1890s, that is. In various
ways it is emblematic of a century of clinical thinking that
followed.
Sometime in the fall of 1892 a governess working in the outskirts
of Vienna visited her doctor with an unusual complex of symptoms.
The patient presented a physical symptom, a chronic suppurative
rhinitis, combined with a "psychological" symptom, a
persistent olfactory hallucination, the smell of burnt pudding.
Her doctor referred the case to Sigmund Freud, who ultimately
told the patient's story as the case study of "Lucy
R.," in Freud and Breuer's Studies on Hysteria (1955
(1895)). There Freud described the case as "a model instance
of one particular type of hysteria, namely the form of this
illness which can be acquired even by a person of sound heredity,
as a result of appropriate experiences" (1955 (1895): 122).
Looking back on the case from the other end of Freud's career, it
seems to be a model instance of more than just a type of
hysteria. It anticipates Freud's own evolution toward
psychoanalysis, as well as developments in clinical approaches to
psychopathology both before and after Freud. In the early 90's,
Freud and Breuer hypothesized that "hysterics suffer mainly
from reminiscences."(7) In the Studies, the mind of
the hysteric is seen to be fending off painful memories and
wishes, with unintended symptomatic side-effects. This basic
process of thoughts repressed and resurgent would soon be applied
in pathologies other than hysteria, and ultimately be read into
every detail of 20th century life. Even more ubiquitous in our
time is the presupposition implied by repression, namely, that
there is something to repress, in the form of thoughts exerting
causal powers without entering consciousness. The conception of
an active-but-unconscious realm of mind reigns in both clinical
and cognitive psychology. The study of Lucy R. explicates these
ideas in terms that are familiar still. In addition, the
psychoanalytic method seems already implicitly at work with Lucy
R. Unlike Breuer's treatment of Anna O., for example, with Lucy
Freud abandoned hypnotism as a diagnostic and therapeutic aid,
probing instead for remembered associations and achieving a
"talking cure."
Yet at the same time the case of Lucy R. is not yet laden with
apparatus and theory that Freud would later develop. Ego, Id,
Superego, and the specific complexes from infancy all lay in
Freud's future. More important, in the Studies Freud still
clearly conceived of psychopathology as originating in traumatic
experience. Later, he would relocate the origins of pathology in
repressed fantasies and wishes, a reorientation that decisively
influenced the subsequent development of psychoanalysis. In the
earlier, "experiential," conception, Freud showed his
affinity with the great 19th century theorists Charcot (with whom
Freud studied) and Janet. And, conveniently, this orientation has
reemerged as a central contemporary issue. Although hysteria has
fallen out of terminological favor, both its symptoms and
traumatic etiology still echo in contemporary clinical taxonomy
and theory (Kihlstrom 1994). For the dissociative disorders in
particular, a frequent cause is real, not merely imagined,
trauma. Lucy R., as Freud interpreted her experience, provides a
straightforward example.
For these reasons I turned to Lucy R. as a model to approach
within the connectionist framework. As in all of his case
studies, Freud used his subject as an object lesson from which he
drew specific conclusions. As we revisit Freud's fable, we will
examine the conclusions he drew and draw some new ones as well.
"Lucynet," the
simulation of Lucy R.
Representing Lucy R.'s phenomenology
Lucy R. also enjoys the curious distinction of having been
the target of an earlier attempted computer simulation, which was
described but not implemented by Cornelis Wegman (1985). In the
epilogue to his heroic effort, Wegman estimated that the actual
implementation of the model would require at least five years of
programming work. How did the case of Lucy R., one of Freud's
briefest, get so complicated? The complexity, I suggest, reflects
the limitations the approach taken, which was drawn entirely from
classical Artificial Intelligence in its heyday, before the
reemergence of connectionism. A brief look at Wegman's work shows
the limits of classical AI as a concrete modelling tool, suggests
the unique powers of connectionism, and offers an initial
foot-hold on "Lucynet," our sequel to Freud's study.
Wegman based his efforts on a sophisticated theory of
"knowledge structures" and their modifications, Roger
Shank's theory of scripts (Shank and Abelson 1977). A script is a
framework for knowledge about actions or other sequences of
events. To define a script, one draws from a repertoire of
actions (of which some are basic), each action having specified
effects on the world. The problem unfolds from the words
"define" and "specify": Every change, and all
its relevant or probable consequences, must be programmed by
hand. Any genuine interaction in the world demands a huge script
for its description. The one event from the Lucy saga that Wegman
fully scripts accordingly implicates seventeen separate actions
fulfilling ten distinct goals and plans for their achievement.
Being an outline and not an implemented program, there is no
guarantee that even this level of detail will be enough. His
initial scripting is certainly not enough, Wegman notes, to
incorporate the proposed mechanisms of hysteria, and thence he
carefully and explicitly adds each of the following to the
expanding model: Affect, arousal, facial expression, abreaction,
working-over, episodic memory, and several others. Significantly,
a separate component called "consciousness" appears in
the flow chart in order to enable the functions of attention and
repression. (For a similar exegesis, but much less sympathetic to
Freud, see Cummins 1983.)
The exercise has the enormous value of flushing out unnoticed
ambiguities is Freud's hypotheses. But even if the model led to a
working implementation, it would leave open the question which if
any of the many installed modules was real. Like the epicycles of
Ptolemaic astronomy, every module in this sort of model is a
kludge, hand-built to do just what Freud (as interpreted by the
would-be modeler) supposes. A more powerful demonstration, in
contrast, would be one that requires less programming
intervention, operates according to a few highly general
principles, and yet exhibits several of the symptoms and
responses in parallel with the case study. A model of this sort
has the capacity to exhibit the target phenomena as emergent
side-effects of more basic and general functions, rather than as
the explicit result of a deliberate program. This in turn
suggests new hypotheses and tests in the target domain.
Connectionist models, when they work, have these attractive
features. Indeed, connectionism makes a virtue of simplicity. The
simpler the model, the more basic and general will be the
mechanisms explaining its functional behavior, resulting in more
powerful explanatory hypotheses in the real world.
To construct Lucynet, then, I took the minimalist approach of
radical simplicity, as afforded by connectionism. Network design
was guided by the observations reported by Freud, which I took at
face value (pacé Crews 1993, Grünbaum 1984, and other critics
of Freud's self-fulfilling observations). Lucy's primary
symptoms, unlike those reported elsewhere in the Studies,
were perceptual hallucinations, a smell of burnt pudding and the
smell of cigar smoke. To understand these symptoms, Freud probed
Lucy's conscious memories and eventually uncovered episodes that
Lucy had apparently repressed. But although Lucy would not easily
recall them, these episodes were initially fully conscious. The
goal of the model, then, could be initially restricted to
capturing the conscious world of Lucy's perceptions, representing
both a sequence of perceived events, some of them traumatic, and
the recollection of those events later on, including their
"conversion" into symptoms. The case study mentions
many details of Lucy's background and current life, but the
specific and significant players in Freud's reconstruction of the
case turn out to be few. As a prelude to setting the simulated
psychodymanics in motion, I compiled the salient elements from
Lucy's reports. The first is the head of the household, a
widower, and director of a factory outside of Vienna (the
"Director," for short). No less important in Lucy's
narrative are the Director's two children, Lucy's pupils.
Although each of the two girls would have been separately and
complexly represented in Lucy's consciousness, for the purposes
of understanding her neurosis it was sufficient to treat them as
a single element ("Children"). The several servants
working alongside Lucy can be similarly conflated. One other role
repeats in important moments in the study, a guest of the
director, in one case female and in another male. But as the
study unfolds, these two also occupy an interchangeable
functional role, abbreviated as "Guest." In Lucy's
experience, these key players are not inert, but among their many
deeds just one plays a recurrent and significant role in her
story: the attempt by each of the guests to kiss the children.
These events ("Kissing" in short) will be narrated
below. Lucy's "lived world" also features intense
feelings. "Love" and "Distress" are
prominent, along with the subjective sensations of her chronic
rhinitis. Last, but not least, is her perception of burnt pudding
and cigar smoke, both the real percepts during moments explicitly
identified in the case study, and the later recurrent
hallucinations.
In sum, these ten explicit elements within Lucy's unfolding
experience compose an initial "alphabet" for Lucynet.
Each would have been a complex internal representation, but in
pursuit of the minimal model we can regard each as a distinct
whole, with varying degrees of prominence from moment to moment
in Lucy's history. Different scenes from the saga, then, can be
represented by combining subsets of these, as letters might
combine to form words. In Lucynet as in Lucy herself, the
elements are not isolated, however. Connectionism borrows from a
long psychological tradition a single highly general conception
of the interaction of ideas, namely, association. Potential
"elements" in conscious thought can be activated by
associated thoughts, or by inputs from the external world. Which
elements are most active at any moment depends on the combination
of these influences. In keeping with the radical minimalism of
the approach, the activation of any unit at any time was
proportional to the sum of its immediately preceding inputs only
-- units retained no activation from the previous cycle. By these
broad strokes then, we have built an architecture for Lucynet
consisting of ten elements -- ten processing units -- suggested
by Lucy R., with the potential for interaction both among the
elements themselves and from the outside. This architecture is
shown in Figure 1. (For a similar approach to modelling memory,
see McClelland and Rumelhart 1986.)
[[Please place Figure 1 about here]]
The narrative of learning, and the lessons of trauma
Experience changed Lucy. Whether trivial or traumatic, each
episode in the case study left its traces, and so each may be
regarded as an occasion of learning. Connectionism captures these
experience-driven changes through a process of changing
association strength governed by overarching "learning
rules." In a network with the simple architecture of
Lucynet, we can use a simple form of a very general learning rule
known as the delta rule (McClelland and Rumelhart 1986). To a
first approximation, the delta rule works as follows: For each
cycle of processing, the current level of activity in a unit is
compared to the current sum of all inputs to the unit. The
connection strengths among the units involved are adjusted so as
to reduce this difference. (For details, see Lloyd 1994.) In
general, delta rule learning produces networks that are good at
associative learning. When Lucynet receives the paired inputs,
"Director" and "Children," the delta rule
increases the connection strengths between these two units.
Subsequently, if Lucynet is presented with either input alone, it
will tend to reproduce their combination, the learned
association.
The extent of learning with each cycle of operation is governed
by a crucial variable, the learning rate coefficient. In
connectionist models, this learning rate is kept very low
(usually around 0.05) to prevent the learning of one association
to interfere with the learning of others. As a consequence,
network learning traditionally requires massive repetition of
inputs to be learned. With a low learning rate, the same network
can learn a number of associations. As a prelude to Lucynet's
bumpy ride, I trained the network on a number of background
associations that would have characterized Lucy's regular
associations in her job. (Some examples: "Director +
Children," due to the obvious familial links; "Rhinitis
+ Distress," reflecting Lucy's chronic complaint;
"Children + Love," following Lucy's repeated statements
of fondness for her charges.) The network had no trouble learning
these associations and reproducing them when partial inputs were
provided. In terms of the model, for any given sensory input,
Lucynet "recognizes" it (= corresponding unit
activation) and experiences "conscious associations"
with it (= secondary, weaker activations), both in plausible
correspondence to a simple associative psychology conjectured for
Lucy herself. During testing, these associations were manifest
with the processing cycle immediately following the test input.
The network did not need to "settle" through multiple
cycles to display its associative pattern completions.
Both Lucy and Lucynet are severely challenged by several
subsequent events. Freud identified these episodes as traumatic,
although weakly so. To represent these in the changeable web of
Lucynet, I tested a crucial hypothesis, the sole modification of
connectionist minimalism: An essential concomitant of
traumatic experience is learning at an abnormally high learning
rate. One main effect of a high learning rate is obvious.
Patterns of inputs presented with a high learning rate will be
"branded" into a network, swamping prior learning with
new associations. In Lucynet, the "traumatic learning"
effects occurred with learning rates over 0.3. These effects were
increasingly complex, as the subsequent stages of the network
will show. Furthermore, at a high learning rate, large effects
follow single exposures of patterns to be learned. In this
respect, the learning-rate hypothesis corresponds to a fortunate
fact about most traumas -- the traumatic event is isolated in its
intensity among more ordinary, nontraumatic experiences. The
story of Lucy R., then, was reduced in Lucynet to a prelude of
unexceptional associative pattern learning, followed by a
sequence of single exposure learning trials, where each of Lucy's
traumas was modelled by just one exposure, at a
"traumatic" high learning rate, to a pattern
corresponding to each trauma from the case study.
First, I followed Freud in a slight romantic excess. Lucy's
troubles began with falling in love with her boss, the factory
director and father of the children in Lucy's care. Freud
imagined Lucy's passion beginning with a single meaningful
conversation, a sudden and dramatic psychological change. The
first pattern for "traumatic learning" was accordingly
"Director + Love." The results were as expected. After
learning, the background associations involving both units were
overwhelmed by the new mutual associations of love. Table 1, row
I, displays Freud's account of the moment and its effects,
together with their re-creation in Lucynet.
[[Please place table 1 about here.]]
Lucy's love for her employer infuses her reactions to several
other events. The first of these is a scene that "crushed
her hopes" (118) of a real relationship with the director.
The blow came following a visit from a female acquaintance. As
the guest prepared to leave, she kissed the two children on the
lips. Later, the director shouted at Lucy that such a breech of
sanitation was intolerable. If Lucy permitted it to happen again,
she would be dismissed. Freud describes this moment as traumatic,
the "operative trauma" in the case. The case study is
unclear about the immediate effect of the episode (which occurred
well before the encounter with Freud). The Lucynet simulation of
the event suggests some plausible conjectures. The input for
learning is the complex "Director + Guest + Kissing-children
+ Distress." As expected, subsequent tests after learning
showed a pronounced pattern completion effect: Presentation of
any one element of the "trauma" led to a pronounced
"recall" of the other elements. The sole modulation of
this emphatic recall showed a continuing influence of the already
established association of units representing the Director and
Love. The episode model appears in Row II of Table 1.
DSM IV (American Psychiatric Association, 1994) lists the
following phenomenological symptoms for Post-traumatic stress
disorder:
B. The traumatic event is persistently reexperienced in one (or
more) of the following ways:
(1) recurrent and intrusive distressing recollections of the
event, including images, thoughts, or perceptions....
(2) recurrent distressing dreams of the event....
(3) acting or feeling as if the traumatic event were recurring
(includes a sense of reliving the experience, illusions,
hallucinations, and dissociative flashback episodes)....
(4) intense psychological distress at exposure to internal or
external cues that symbolize or resemble an aspect of the
traumatic event.
(5) physiological reactivity on exposure to internal or external
cues that symbolize or resemble an aspect of the traumatic event.
All of these are plausible elaborations of the pattern completion
effects observed in Lucynet. The basic mechanism of PTSD
suggested, then, is a mechanism for associative learning and
recall operating in a disruptively emphatic way. In Lucynet, the
learned complex has no internal structure and every element is
equally effective in recreating or "reliving" the
experience. As a result, a range of inputs, including trivial
reminders of the event, may be sufficient to kindle the whole
traumatic pattern.
These observations were very much as expected, given the initial
understanding of the delta rule and the effects of increased
learning rates. Moreover, the apparent analogy between network
learning and PTSD symptoms has been independently noted by Li and
Spiegel (1992), who proposed (but did not implement in a model)
that trauma be modelled as pattern-completion effects following
an emphatic inputs. However, Li and Spiegel did not anticipate
the side effects of traumatic learning when traumas compound. For
Freud, Lucy, and Lucynet, the more interesting and complex
developments lay ahead.
Associations dissociated: Effects of multiple traumas
As it happened, the unpleasantness in Lucy's household
recurred. Some weeks after the director's outburst, another guest
repeated the attempt to kiss the children. This time the director
flared up at the guest, the Chief Accountant at the factory and a
regular visitor. To Lucy, however, the scene was "a stab at
my heart" (120). One other feature was prominent in Lucy's
eventual memory of the scene, the smell of cigar smoke. As in the
case study, the Lucynet representation of this scene (which Freud
called an "auxiliary trauma") closely parallels the
previous traumatic scene, with the noted addition of the smell of
cigars. The learned pattern, then, was the complex "Director
+ Guest + Kissing-children + Cigar-smoke + Distress."
For Freud, it was this scene, rather than the first, that was the
origin of Lucy's hysterical symptoms. One might expect that the
large overlap between the operative trauma and its auxiliary echo
would only reinforce the emphatic learning and pattern completion
effects. Yet in Lucynet the responses to the next cycle of
traumatic learning departed from the PTSD-like symptoms observed
earlier. The first surprise is the nearly complete disappearance
of the pattern completion effects (Row III, Table 1). None of the
elements of the two traumatic scenes evokes the others. The
recall of "distress" and of the main event, the attempt
to kiss the children, both seem to vanish. This paradoxical
loss of exactly the pattern expected to be retained is the neural
network analogue of repression.
Instead of accurate recall of the learned
pattern, the network exhibited an unexpected replacement. To
several input probes, Lucynet responds with the activation of the
unit representing the smell of cigar smoke. Prior to this point
in the simulation, when an input was sent to a single unit of the
network, the strongest response was invariably in that same unit;
we interpreted that response as the perceptual registration of
the input. Now, after compounded trauma, the strongest network
activation no longer corresponds to the input, but is found in
another unit altogether, the "Cigar" representation. An
input is thus converted into a new percept, an activation formed
in the absence of its appropriate input. Lucy experienced a
recurrent hallucination of cigar smoke. Lucynet exhibited an
"inappropriate" activation of its "Cigar"
unit, without the corresponding input. The paradoxical
emergence of a maximal activation without the corresponding input
is the neural network analogue of hallucination.
What is going on here? Freud drew his principle morals from the
case study at this point, offering a mechanism to explain the
twin observations of repression and symptom formation. Repression
begins with a deliberate and conscious effect to banish a painful
memory from recall. Memories cannot be erased, however. Instead,
they are merely isolated:
This effort to repudiate the hated memory is
thwarted when something in the environment strongly reminds one
of the original trauma. In the case of Lucy R.,
The "convergence" is unbearable,
however:
In short, Freud imagines a dual process:
repression, followed by conversion. His conception of these
processes posits a discrete 'nucleus of thoughts,' explicit
mental representations ("reminiscences") that are
driven from consciousness, but nonetheless reassert themselves in
disguise as symptoms. Because these unbearable thoughts continue
to exist, Freud cheerfully posited an explicit unconscious
'system' to house them. This conception would be elaborated
throughout his career (e.g. Freud 1957 (1915)), but is already
presupposed here.
Lucynet models the significant symptoms of Lucy R., and develops
those symptoms through a consistent analogue of Lucy's experience
in the months before her visit to Freud. But, as figure 1 makes
clear, Lucynet utterly lacks the mechanism Freud imagined.
Connectionism thus offers a different way of thinking about what
occurred in Lucy R., and in cases of compounded trauma in
general. Lucynet's "symptoms" are explained by the
conjoint effects of the "traumatic learning" of
overlapping patterns and the delta learning rule. With a single
trauma, the delta rule leads to a pronounced increase in
connection strength among the units involved in the traumatic
pattern. A single exposure leads to "overlearning," as
discussed above. When that same pattern partly repeats, units
involved in the pattern receive a flood of input as the external
input combines with the massive lateral inputs along the
positive, overlearned connections. The delta rule accordingly
compensates for this overload by driving down the weights
on connections. Since subsequent patterns are also traumatic
(that is, are learned at a high learning rate), this inhibitory
effect is dramatic. When subsequent patterns partly overlap, the
maelstrom of delta rule effects rapidly becomes intractable. In
this case, the new element, "Cigar smoke," is exempt
from the inhibition affecting the other units, and the network
develops the tendency to respond as if that element were present
in response to several unrelated inputs.
Lucy's story did not end with the episode just modeled, however,
nor was the hallucinated cigar smoke her initial complaint. One
more "traumatic" scene followed. In part because of her
troubles in her household, Lucy considered quitting her post, but
at the price of losing her ties to the children. This conflict of
emotions was particularly acute one day as she played with the
children just after receiving a letter from her mother, back in
Scotland. Just at that moment a pot of pudding on the stove began
to burn. Freud reasoned that the conflict of feelings at just
that moment was intense enough to constitute a trauma (115), and
the smell of burnt pudding its conspicuous marker. As a result,
Lucy would hallucinate that smell, her principal complaint
henceforth.
Although the pudding only burns once, it seems likely that the
emotional tumult that accompanied the smell recurred throughout
this period in Lucy's life. If a prior moment of conflict had
already been traumatic, then the scene with burnt pudding might
have been a repeating, "auxiliary" trauma. In that
case, the psychodynamics underlying this symptom would be
parallel to the origin of the cigar smoke hallucination, where
the first trauma creates massive association, but its repetition
massive inhibition and dissociation, save for new elements, which
"pop out" as conspicuous new symptoms. Alternatively,
Freud proposes that in general an initial trauma and its
auxiliary repetition can "coincide," with conversion
occurring as an immediate effect (124). In this case, the
immediate recall of trauma would itself be traumatic, and even an
isolated trauma would become self compounding.
Each of these interpretations suggests different simulations at
this stage in Lucynet. Rather than pursue them, however, I kept
as close as possible to the case study itself. Freud recounts a
single traumatic moment on the theme of leaving the children, a
moment also marked, as it happens, by Lucy's rhinitis, and so for
Lucynet I input one pattern for traumatic learning:
"Children + Rhinitis + Burnt pudding + Distress." Row
IV of table 1 shows the results of this next stage of Lucynet
traumatic learning. The four elements of the traumatic pattern
are bound into a tight associative unit, and the responses
parallel the PTSD-like responses also shown in row II. Unlike the
cigar smoke hallucination, the smell of burnt pudding does not
dominate the response to other inputs. Thus, in the Lucynet
framework, it is a pronounced association rather than a clear
"hallucination." However, the association is very
strong, and elicited by single inputs which Lucy might have
encountered routinely: Children, her rhinitis, and her ongoing
distress. This simulation also suggests that the memory of the
traumatic scene would be readily available, if not intrusive. So
it was for Lucy. Freud began his interrogation by asking whether
the smell of burnt pudding reminded her of anything, and she was
quick to recount just this scene. But that is another story, one
of therapy and cure.
Remembrance and catharsis
Having created what may be the world's only neurotic neural
network, I felt compelled to restore my creation to full
(simulated) mental health. Again, I turned to Freud and Breuer
for guidance:
In the Studies, this was called the
"cathartic technique," which Freud would later call
"the immediate precursor of psycho-analysis; and, in spite
of every extension of experience and of every modification of
theory, ... still contained within it as its nucleus" (Freud
1955 (1924): 194).
The network version of catharsis, then, will consist of the
re-exposure to the traumatic stimuli. Freud and Breuer stress
that the reminiscence of the scene must be accompanied with its
original affect. Thus, within the connectionist framework at
least some of the original traumatic intensity must accompany the
catharsis. I modelled the overall catharsis by re-exposing the
network once to each of the traumatic patterns, using a learning
rate coefficient set at half that of the original traumatic
learning. As in the case study, the patterns were presented in
reverse order, as Lucy herself (with Freud's prompting) recounted
them.
Catharsis led to cure for Lucynet as for Lucy. Re-exposure to the
second auxiliary trauma led to a reduction of associative
intensity of inputs to the "burnt pudding" unit (in
Lucynet), and a gradual reduction in the hallucination (for
Lucy). Re-exposure to the earlier traumas led to a more dramatic
reversal. In Lucynet, the "hallucination" of cigar
smoke and the accompanying "repression" of the
traumatic pattern both disappeared completely, replaced with a
normal set of associative links among parts of the traumatic
pattern. (For example, the input "Guest" yields
activation in "Guest," "Kissing-children,"
"Cigar smoke," "Director," and
"Distress.") For Lucy too, the hallucinated cigar
vanished at once. One trauma, however, neither patient nor
network could overcome. Both finished their histories with an
abiding (if secret) love for their boss. Lucy confessed as much
in her last session with Freud; Lucynet showed an implacable
two-way association between "Director" and
"Love."
To re-experience a trauma one must first remember it. Usually,
any number of cues leads to retrieval of a learned pattern. But
when a memory is repressed, whether in artificial or human neural
networks, many of those associative paths are blocked. How, then,
is the repressed pattern recovered? Lucy R. made her way back to
the operative trauma by patient association. "At my
insistence," Freud wrote, "a picture gradually emerged
before her, hesitatingly and piecemeal to being with" (119).
So far, Lucynet only displays its immediate response to an input,
its "first associations." This made the
"repression" of the operative traumatic pattern a
barrier to its recall that could not be overcome by any
combination of inputs. To further explore this issue, I
redesigned Lucynet to simulate a purely internal sequence of
thoughts, a simulated "stream of consciousness." To do
this, I took the current activation following an initial input,
and re-input this activation as a new input. In essence, each
pattern of internal activation in the network thus generates its
successor, following only the associative paths established
between units in the course of the network history. I recorded
each of these activation states over ten cycles of recurrent
network "reflection."
Examples of the network's changing internal operations are shown
in Figure 2. Each panel shows the initial input to the network in
the leftmost column, labelled "I." The columns labeled
"A" then show ten cycles of response. (The size of the
dark squares indicates the magnitude of positive activation.
Light squares signify negative activation values, i.e.
inhibition.) Cycle 1 is the net's "percept" or
immediate response to the input; this is the activation I've
interpreted as an analogue to Lucy's state of consciousness at
turning points in the case study. Each subsequent cycle is the
network's purely internal response to its previous state of
activation. For comparison, figure 2 depicts just the evolving
responses to input in the "cigar" unit. Until far along
in the traumatized training, the net displays a fairly
predictable associative "psychology," in which the
network settles into a stable state of self-sustaining
activation. Two of the background associations (prior to any
trauma) are initially apparent: "Director + Guest"
(reflecting the director's noted propensity to entertain
visitors) and "Director + Guest + Cigar" (following the
favorite pastime, noted explicitly by Lucy, of her boss and his
male acquaintances). The cigar input "reminds" Lucynet
of these associations, and the net settles into a stable
recreation of those associative patterns, with echoes of other
connections (e.g. "Children + Love").
[[Please place figure 2 about here.]]
Following the overlearning of "Director + Love,"
Lucynet's soliloquy changes. The cigar still reminds it initially
of guests and the director, but once the latter is "in
mind," all further thoughts follow the love connection. That
stable association is then overthrown by the operative trauma,
"Director + Guest + Kissing-children + Distress." As
soon as the background associations carry the network toward
"Guest" and "Director," it is this most
recent "trauma" that dominates, modulated by the prior
strong associations between "Director" and
"Love."
Up to this point, the network behaves like most connectionist
models in that it "settles" into a stable pattern of
activation in the absence of further inputs. Simple assumptions
about associative psychology and the intense learning of a
traumatic pattern explain its behavior. But all this changes in
panel D, showing the network's internal processing following the
auxiliary trauma, which repeated the preceding trauma with the
addition of the smell of cigars. First, the "Cigar"
input fails to recreate the traumatic pattern (as discussed
above). But rather than settling into a stable response, even
without new input the "neurotic" network oscillates
between states of excitation and inhibition, each cycle a
flashback to an earlier scene in the case study. Significantly,
at cycles 4 and 5, the "repressed" traumatic pattern
briefly reappears, to be promptly canceled in cycle 6. The
compounding of traumatic inputs has not simply erased the history
of network learning. That history has radically altered network
function, and even left a path for its explicit reconstruction.
But the path is a tortuous one. Despite its simplicity, Lucynet
captured this aspect of the case study by suggesting the
possibility of the recall of repressed content. (Other
implications of recurrent processing will be considered below.)
Discussion: From the 90s to the 90s
To summarize, the history of Lucynet follows the case study of
Lucy R. by simulating the learning of plausible background
associations followed by a series of "traumatic"
inputs, learned via single exposures with an abnormally high
learning rate coefficient. A second sequence of learning followed
the course of therapy, re exposing the network to the
"traumatic" input patterns via single exposures at an
intermediate learning rate. As a result, the network exhibited
robust analogues of three of Freud's most salient observations of
Lucy: two olfactory hallucinations and the repression of memory
for key episodes of symptom formation. These symptoms emerged and
disappeared from the network at moments corresponding to their
emergence and disappearance in Freud's chronology of the case.
The pattern of symptoms emerged as a side effect of the
simulation of Lucy's experience and the operation of the neural
network, rather than as a direct result of programming or
explicit training to produce these responses.
These are intriguing results given the radical simplicity of
Lucynet -- ten units only, governed by a single activation
equation and a single learning rule. From ten processing units to
the tens of billions in the human brain is a sobering leap. We
would not wisely conclude anything about the specific psychology
or physiology of Lucy R. or anyone else based on Lucynet. But we
can use Lucynet as a heuristic model and foil for theories of
hysteria and dissociation. Its simplicity leaves no place for
special processes to hide, and thus reveals and questions some
widespread assumptions about the mechanisms and etiology of
hysteria and its modern descendants.
Perhaps the most useful lesson of Lucynet lies in its deep
challenge to what might be called the archival model of memory.
By this I mean the conception of memories as fixed records or
"reified contents" that can pass in and out of
consciousness, and be variously influential or dormant over time.
Even in the Studies, Freud clearly conceived of ideas of
all sorts in this way:
Once thoughts are reified as special sorts of
fixed objects to be manipulated by the mind, most of the Freudian
mechanics follows as a matter of course. If thoughts exert
influences on behavior and consciousness without themselves
becoming conscious, then they must sometimes exist in the
unconscious (a sort of specialized processing module) and,
moreover, some sort of mental executive must take on the task of
moving thoughts in and out of consciousness, and in an out of
conscious or unconscious play. This way of thinking about
thoughts certainly meshes smoothly with the computational model
of mind that has long dominated cognitive science (Erdelyi 1985).
These days the archival model of memory has been explicitly
disavowed by all. Extensive work in cognitive psychology has
shown recall to be construction of a memory rather than
its retrieval. Connectionists have certainly encouraged this
reconception of memory by showing how explicit patterns of
activation can be stored implicitly in the form of matrices of
connection weights. Memory to a connectionist is a disposition to
reform patterns of activation, rather than extract them from some
form of storage.
Yet in discussions of psychopathology the archival model and its
attendant mechanisms still operate, even if covertly. For
example, in his excellent review of dissociative disorders,
Kihlstrom (1994) notes that a number of disorders involve
failures of recall, but the failures are temporarily or
permanently reversible. (This characterizes the DSM IV disorders
of dissociative amnesia, dissociative fugue, and dissociative
identity disorder.) "Reversible memory disorders are
disorders of retrieval; they occur because the individual cannot,
at the moment, gain access to memories that have been adequately
encoded, and remain available in storage" (Kihlstrom 1994:
379). Here the image of the archive is explicit, although one
could alter the terminology to depict storage as a merely
dispositional, connectionistic storage. But what Kihlstrom
concludes from his observation requires an archival view:
"Retrieval, and accessibility, are phenomena of
consciousness as they entail bringing available memories into
phenomenal awareness" (ibid.). Memories, in short, move in
and out of the spotlight of awareness; with the reification of
memory comes the reification of a special processor,
"consciousness." Kihlstrom and Hoyt (1990) make this
explicit as follows:
Thus a conception of memories as fixed records
brings along with it a model of mind in which conscious and
unconscious mental processes can unfold in parallel, passing
thoughts back and forth. The evidence of disintegrated cognition
has suggested to a long line of researchers the existence of
parallel executives. The first to argue along these lines is
probably Plato, who interpreted conflict of the will as evidence
for distinct faculties of mind (Republic, Book. IV). It
persists at the origins of clinical psychology not only in Freud
but also in Janet and James, and in numerous contemporary sources
(e.g. Hilgard). Even the psychopathologists Li and Spiegel, in
their discussion of the import of connectionism for understanding
dissociation, declare a need for the parallel operation of two or
more information processors (Li and Spiegel 1992: 145)
Lucynet gets away with much less. One processor accommodates both
Lucynet's preserved "normal" associative processing and
its dissociated dislocations. Yet, for all its simplicity, once a
certain learning history has transpired, the network ceases to be
a passive responder to input stimuli. Figure 2D depicts a new
stage in Lucynet evolution and an intriguing moment in
connectionist modeling. At this point, patterns vie for
expression. While some strut and fret their hour upon the stage,
others are (temporarily) heard no more. When various trains of
network thought exclude each other, we observe the network
analogue of dissociation. But, as always in this study, there is
no off stage orchestration. There are just the thoughts on the
surface, interacting with each other. The functions of
integration or disintegration, making conscious or repressing,
are not administered by an agency separated from the thoughts
(patterns) themselves.
Instead of a special processing system to monitor and manipulate
explicit unconscious representation, through learning Lucynet
undergoes widespread changes in the connection weights
between conscious elements. These weights define the dispositions
of elements to activate one another. They are
"unconscious" in the sense that they are part of the
implementation of the network rather than its explicitly
represented content, analogous to the physiology of synapses in
the brain. But this remains a different and less robust
conception of the unconscious than that of the archival model.
In addition to its dispositional, connectionist storage of
memories, Lucynet exhibits a further break from the archival
model: In Lucynet, encoding of new memories alters the
encoding of the old. Previously learned patterns change as an
immediate side effect of traumatic learning; no special
re-enactment of old memories is required. Connectionist modelers
usually go to great lengths to prevent the interference of
old learning by new, with the goal of accurate reconstruction of
discrete learned patterns (Hetherington and Seidenberg 1989;
Kortge 1990; Murre 1992). But in Lucynet this interference is
exactly the source of both the negative and positive
"symptoms" -- dissociation from the overlearned past,
and the insertion of a "perceptual hallucination." In
most models, interference effects are meaningless noise, but
within the guiding framework of a clinical study, Lucynet's wild
ride remains interpretable.
The study of Lucy R. has thus become a twice-told tale. Its
second telling, as Lucynet, has elided much of the humanity of
the first, but it has preserved the main episodes and the main
effects noted in Freud's version. The new tale has added a
crucial subtext, the fundamental hypothesis that one form of
psychogenic pathology can originate when stimulus patterns are
subject to intense single exposure learning. But a single episode
of "traumatic learning" did not generate the
dissociative effects typical of hysteria. For this, our simulated
subject needed a history of simulated suffering. Only then did
the network become both neurotic and interesting.
Like any story, the new fable of Lucynet is open to many
interpretations. Given its simplicity, Lucynet provides no direct
evidence about any aspect of human psychology. But it does show
something of what is possible on a shoestring. In that spirit, it
suggests a few possible morals -- avenues of inquiry worth
noting for future clinical research:
1) Psychopathology is a narrative. The scientific emphasis
on efficient causation, experimental method, and statistical
significance leads to a search for "stories" of
pathology in which there are just two episodes, a single cause
and its particular effect. Lucynet developed its most revealing
syndrome only after a sequence of unique events, each
contributing to a complex outcome. In the huge networks that are
each of us, every experience and every response reflects the
remembrance of things past. Our past experience may not merely
provide a general backdrop, but instead contribute in specific
ways to otherwise inexplicable responses. Freud, of course, would
agree, and most clinicians (but not most insurers). This
complicates the understanding of pathology in general, as well as
diagnosis and treatment of specific cases. It also threatens the
rigor of clinically based science, leading to charges (such as
those levelled at psychoanalysis) that it is psuedoscience (e.g.
Grünbaum 1984, 1993). Connectionism may offer a middle ground,
by allowing for models sensitive to the cumulative effects of
personal history, but still constrained by the basic
computational capacities of networks. Such models afford further
controlled exploration of several variables that may be
clinically important.
2) To interpret a clinical narrative, one must understand the
perceptual, cognitive, and affective world of the subject.
Models like Lucynet are "loose" in several senses.
First, they rest on an initial assignment of meanings to network
architecture and possible patterns of activation. Second, the
traumatic learning is indiscriminate, branding both the central
and the trivial elements of a horrific scene into the traumatized
memory. But a compounded trauma has the further effect of
inhibiting some links within the repeated trauma while enhancing
others, leading (in Lucynet, and perhaps in humans) to
modifications in subsequent encodings and ultimately to
dissociative phenomena. These complex effects in turn depend
on the perceptual categories that underlie the recognition of
elements as "same" or "different" from one
exposure to the next. This category assignment will be
sensitive to the ramifying effects of compounded trauma, and to a
host of developmental and idiosyncratic differences. If
retroactive memory interference occurs in us as well, unravelling
a dissociated life narrative may be even more difficult. Event
memory traces may not merely be hidden but altered.
3) Connectionism is a multi-level modeling tool.
Connectionists often celebrate the "neural inspiration"
of their approach, and in recent years have worked toward ever
increasing biological realism. The connectionist approach
naturally lends itself to the simulation of biological neural
networks. But it nonetheless also lends itself to the simulation
of other complex phenomena, especially systems subject to
multiple simultaneous constraints or internal interactions. Our
minds, described at the psychological level as arenas for the
interplay of thought, are such systems. It does not matter that
Lucynet is biologically unrealistic, or that the delta rule
probably does not describe the waxing and waning of synaptic
efficacy. What does matter is that the model offers a consistent
representation of a domain, so that the model's behavior can be
compared with that of entities in the domain. As models become
sufficiently general, they become theories of the domain.
Lucynet, as a pilot study, cannot pose as a theory of
dissociation. But it could indicate a family of psychological
models that may ultimately cohere as a theory of some aspect of
psychology. That ultimate theory will be no more biological than
Lucynet, but none the worse as a theory at its own level.
4) Without a central executive, anything is possible. Just
as digital computers suggest (falsely) an image of unfailing and
unflappable rationality, connectionist networks project the image
of steady pattern-completion and solid, predictable, rote
association. They are built to work. But no law enforces this
expectation. In fact, these networks are delicate hot-house
flowers, reared in the most rigid and contrived learning
environments. In the erratic climates of human experience, such
nets would fail. Lucynet became a failure as a pattern
associator, but an interesting and suggestive one. After his
reading of Charcot, Janet, Breuer, and Freud, William James
commented:
Between "chaos come again" and the
"neat notions of cognitive and active powers" we find
the vast middle ground of connectionism. In its mechanics and its
poetics we may oneday find a new understanding of both
psychopathology and everyday mental life.
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