We cannot help interpreting Nature as an organisation of
parts-within-parts, because all living matter and all stable inorganic
systems have a part-within-part architecture, which lends them
articulation, coherence and stability; and where the structure is not
inherent or discernible, the mind provides it by projecting butterflies
into the ink-blot and camels into the clouds.
To sum up: in motor hierarchies an implicit intention or generalised
command is particularised, spelled out, step by step, in its descent to
the periphery. In the perceptual hierarchy we have the opposite process:
the input of the receptor organs on the organism's periphery is more and
more 'de-particularised', stripped ofirrelevancies during its ascent
to the centre. The output hierarchy concretises, the input hierarchy
abstracts. The former operates by means of triggering devices, the
latter by means of filtering or scanning devices. When I intend to write
the letter R, a trigger activates a functional holon, an automatised
pattern of muscle contractions which produces the letter R in my
particular handwriting. When I read, a scanning device in my visual
cortex identifies the letter R regardless of the particular hand that
wrote it. Triggers release complex outputs by means of a simple coded
signal. Scanners function the opposite way: they convert complex inputs
into a simple coded signal.
VI
A MEMORY FOR FORGETTING
Mais où sont les neiges d'antan?
François Villon
'I've a grand memory for forgetting, David,' remarks Alan Breck in
Kidnapped
. He speaks for all of us. Our fond memories are the dregs
left in the wineglass, the dehydrated sediments of perceptions whose
flavour has gone. I hasten to add that there are of course exceptions to
this -- memories of almost hallucinatory vividness of scenes or episodes
which have some special emotional significance. I shall call this the
'vivid fragment' or 'picture-strip' type of memory -- as distinct from
'abstractive' memory -- and come back to it later in this chapter.
Abstractive Memory
The bulk of what we are able to remember of our own life history, and
of the knowledge we have acquired in its course, is of the 'abstractive'
type. Take a simple example: you watch a television play. The exact words
of each actor are forgotten by the time he speaks his next line, and only
the meaning remains; the next morning you only remember the sequence of
scenes which constituted the story; after a year you only remember that
it was about a tangle between two men and a woman on a desert island. The
original input has been stripped, skeletonised. Similarly with books one
has read, and episodes one has lived through. As time passes, memory is
more and more reduced to an outline, a condensed abstract of the original
experience. The play you saw a month ago has been abstracted by a series
of steps, each of which condenses particulars into more generalised
schemata; it has been reduced to a formula. The playwright's imagination
made an idea branch out into a structure divided into three acts, each
divided into scenes, each consisting of smaller divisions -- exchanges,
phrases, words. Memory-formation reverses the process, makes the tree
gradually shrink back into its roots, as in a trick film played backward.
The word 'abstract' has, in common usage, two main connotations: it
is the opposite of'concrete' in the sense that it refers to a general
concept rather than a particular instance; and in the second place,
an 'abstract' is a summary or condensation of the essence of a longer
document, snch as civil servants prepare for their superiors. Memory is
abstractive in both senses.
This is, as I have already said, not the full story. If it were, we
should be computers, not people. But for the moment let us consider this
abstractive mechanism a little further. Memory-formation is a process
continuous with perception. It has been said that if a visitor wanted
to see Stalin, he had to pass through seventeen gates, from the outer
Kremlin gates to the door of the innermost sanctum, and at each successive
gate he was submitted to a more thorough screening. We have seen that the
sensory intake is subjected to a similar scrutiny before being admitted to
awareness. At every gateway of the perceptual hierarchy it is analysed,
classiffied, stripped of all detail that is irrelevant For the purpose
in hand. We recognise the letter R written in an almost illegible scrawl
as 'the same thing' as a huge printed R in a newspaper headline, by a
scanning process which disregards all details as irrelevant and only
retains the basic geometrical R-design -- the 'R-ness' of the R -- as
worth signalling to higher quarters. The signal can then be encoded in
a kind of simple Morse. It contains all the information that matters --
'it's an R' -- in condensed, skeletonised form, but the wealth of detail
is of course lost. The scanning process is indeed the exact reverse of
the triggering process.
Even those few among the multitude of stimuli constantly impinging on
our senses, which have successfully passed all screenings and thus
achieved the status of a consciously perceived event, must usually
submit to a further rigorous stripping before deemed worthy to be
admitted to permanent memory storage; and with the passing of time
even this skeletonised abstract is subject to further decay. Anybody
who tries to write a detailed chronicle of his doings during the week
before last must be painfully surprised at the rate of decay, and the
amount of detail irretrievably lost.
This impoverishment of lived experience is unavoidable. It is partly
a matter of parsimony -- although the storage capacity of the brain is
probably much greater than most people make use of in their lifetime;
but the decisive factor is that the processes of generalisation and
abstraction imply by definition the sacrifice of particulars. And if,
instead ofabstracting universals like 'R' or 'tree' or 'dog', memory
were a collection of all our particular experiences of 'R's' and 'trees'
and 'dogs' -- a store of lantern-slides and tape-recordings -- it would
be completely useless: since no sensory input can be identical in all
respects with any stored slide or recording, we would never be able to
identify an R or recognise a dog or understand a spoken sentence. We
could not even find our way through that immense store of particularised
items. Abstractive memory, on the other hand, implies a system of
stored knowledge, hierarchically ordered with headings, sub-headings
and cross-references like the entries in a Thesaurus or the subject
catalogue of a library. Some volume may have got into the wrong place,
and some flashy jacket designs might stick out and catch the eye, but
on the whole the order holds.
A Speculative View
Fortunately there are compensations for the unavoidable impoverishment
of lived experience in the abstractive process.
In the first place the scanning process can acquire a higher degree of
sophistication through learning and experience. To the novice, all red
wines taste alike, and all Japanese males look the same. But he can train
himself to superimpose more delicate scanners on the coarser ones, as
Constable trained himself to discriminate between diverse types of clouds,
and classified them into sub-categories. Thus we learn to abstract finer
and finer nuances -- to make the perceptual hierarchy grow new twigs,
as it were.
In the second place, memory is not based on a single abstractive
hierarchy, but on a variety of interlocking hierarchies -- such as
those of vision, taste and hearing. It is like a forest of separate
trees but with entwined branches -- or like our library catalogue with
cross-references between different subjects. Thus the recognition of a
taste is often dependent on cues provided by smell, though we may not
be aware of it. But there are more subtle cross-connections. You can
recognise a tune played on a violin although you have previously only
heard it played on the piano; on the other hand, you can recognise the
sound of a violin, although the last time a quite different tune was
played on it. We must therefore assume that melody and timbre have been
abstracted and
stored independently by separate hierarchies
within
the same sense modality, but with different criteria of relevance. One
abstracts melody and filters out everything else as irrelevant,
the other abstracts the timbre of the instrument and treats melody
as irrelevant. Thus not all the details discarded in the process of
stripping the input are irretrievably lost, because details stripped
off as irrelevant according to the criteria of one hierarchy may have
been retained and stored by another hierarchy with different criteria
of relevance.
The
recall
of the experience would then be made possible by the
co-operation of several interlocking hierarchies, which may include
different sense modalities, for instance sight and sound, or different
branches within the same modality. Each by itself would provide one aspect
only of the original experience -- a drastic impoverishment. Thus you may
remember the words only of the aria 'Your Tiny Hand is Frozen', but have
lost the melody. Or you may remember the melody only, having forgotten the
words. Finally, you may recognise Caruso's voice on a gramophone record,
without remembering what you last heard him sing. But if two or all three
of these factors are represented in the memory store, the reconstruction
of the experience in recall will of course be more complete.
The process could be compared to multi-colour printing by the
superimposition of several colour-blocks. The painting to be
reproduced -- the original experience -- is photographed through
different colour-filters on blue, red, and yellow plates, each of
which retains only those features that are 'relevant' to it: i.e.,
those which appear in its own colour, and ignores all other features;
then they are recombined into a more or less faithful reconstruction of
the original input. Each hierarchy would then have a different 'colour'
attached to it, the colour symbolising its criteria of relevance. Which
memory-forming hierarchies will be active at any given time depends,
of course, on the subject's general interests and momentary state of mind.
Memory cannot be a store of lantern-slides and tape-recordings, nor of S-R
building-blocks; so much is evident. But the alternative hypothesis which
I have suggested -- that memory is 'dissectible' into hierarchies with
different criteria of relevance -- is, frankly, speculative. However,
some modest evidence for it can be found in a series of experiments
which James Jenkins and I carried out in the psychological laboratory
at Stanford University .*
* The results were published in a technical paper [1]; the gist
of the experiment was to show to each subject for a fraction of
a second only (by means of an apparatus called a tachistoscope) a
number of eight or nine digits, and then let him try to repeat the
sequence. The results of several hundred experiments show that a
highly significant number of errors (approximately fifty per cent)
consisted in the subject correctly identifying all numbers in the
sequence, but inverting the order of two or three neighbouring
digits. This seems to confirm that the identification of individual
digits, and the determination of their sequential order, are carried
out by separate branches of the perceptual hierarchy.
Two Types of Memory
The 'colour-printing' hypothesis goes some way towards explaining the
puzzling phenomena of recall, but it is based solely on the abstractive
type of memory, which alone cannot account for the extreme vividness
of the 'vivid fragments' or 'picture-strips' mentioned at the beginning
of this chapter. After some forty years, I can still hear the voice of
the great Austrian actor, Alexander Moissi, whispering the last words
of a dying man: 'Give me the sun.' I have forgotten what the play was
about, even its author it may have been Strindberg, Ibsen or Tolstoy --
except for the hallucinatory clarity of that one fragment, torn from its
context. Such fragments that have survived the decay of the whole to
which they once belonged -- like the single lock of hair on the mummy
of an Egyptian princess have an uncanny evocative power. They may be
auditory -- a line from an otherwise forgotten poem, or a chance remark
by a stranger overheard on a bus; or visual a gesture of a child, a mole
on a schoolmaster's face; or even refer to taste and smell, like Proust's
celebrated
madeleine
(a French pastry, not a girl). 'There exists a
method of retention which seems to be the opposite of memory-formation
in abstractive hierarchies. It is characterised by the preservation
of vivid details, which, from a purely logical point of view, are often
irrelevant; and yet these quasi cinematographic details, picture-strips or
"close-ups," which seem to contradict the demands of parsimony, are both
enduring and strikingly sharp, and add texture and flavour to memory.' [2]
But if these fragments are so irrelevant, why have they been preserved?
The obvious answer is that while irrelevant from the point of view of
logic, they must have some special
emotive
significance -- which
may be conscious or not. Indeed, such 'vivid fragments' are usually
described as 'striking', 'evocative', 'nostalgic', 'frightening', or
'moving' -- in a word, they are always emotionally coloured. Thus among
the criteria of relevance which decide whether an experience is worth
preserving, we have also to include
emotional relevance
. The
reason why a particular experience should have this kind of relevance
may be unknown to the subject himself; it may be symbolic or oblique.
Nobody -- not even a computer theorist -- thinks all the time in terms of
abstractive hierarchies; emotion colours all our perceptions, and there
is abundant evidence to show that emotional reactions also involve a
hierarchy of levels, including some ancient structures in the brain which
are phylogenetically much older than the modern structures concerned with
abstract conceptualisations (see