METAPHORS OF MEMORY by Douwe Draaisma: a brief review and summary.

METAPHORS of MEMORY is a dense and beautifully produced book by Cambridge University Press. It has been translated from the Dutch by Paul Vincent.

Although it contains many illustrations I am not sure it is aimed at the general market - however I worked determinedly through the 241 pages because I found the ideas and the conclusions quite fascinating.

Chapter by chapter the author, Douwe Draaisma, who is a Dutch academic, discusses the metaphors that have been used for memory. He explains where they come from, who thought of them, and how they fit into the theories of the mind and consciousness of the time. He then goes on to consider how well they work as metaphors - what they explain and what they don't, and how they fit in to what went before and what comes after. His conclusion, in his final chapter, is surprising and wonderfully thought-provoking.

Draaisma starts (and ends) with a brief description of Freud's metaphor for memory: the mystic writing pad. I remember something similar from childhood - a pad I could write on with a pointed piece of plastic and the writing would appear in front of me - but when I lifted the top layer and then put it down again the writing would be gone. However, at the back of this I remember seeing a piece of darkly coloured paper, which in Freud's time was waxed. The words I'd written, together with all the other words I'd written were still there. For Freud this was memory. The blank part that had temporarily contained my writing was the layer of the mind which received the stimulus - while underneath was what was retained - the memories.

According to Freud, metaphor was essential in the study of his science. 'In psychology we can describe only with the help of comparisons...we are forced to change these comparisons over and over again, for none of them can serve us for any length of time.' he wrote and this really is the theme of the book - why metaphors are used; not only to help us understand but to help us to expand on what we know and predict. The best metaphor should be heuristic and multi-layered; indicating new links and ideas between the topic (the strange new subject of the metaphor) and its vehicle (the simple, familiar thing it is like). This, I believe, is taking what Professor Roald Hoffmann said in his article a small step further; the metaphor should not just aid the understanding of science but should also lead to new developments and thinking.

Freud also defined scientific creativity as the interplay between 'daringly playful fantasy and relentlessly realistic criticism'. So the metaphor embodies the idea of many disciplines coming together in order to make a new innovatory step; it needs a great cauldron of ideas for a new startling truth to emerge. The metaphor itself mixes - it causes the strange and new can be mixed with the old and familiar so that it is seen in a new way - and once it is seen in that new way then the idea can develop and grow.

The book gives examples of how this has happened in the past - and this is the meat of the book; a series of fascinating examples and anecdotes. For instance thinking of the chemical elements as musical notes arranged in octaves led eventually to Mendeleev's periodic table.

As far as metaphors of memory are concerned Draaisma says they are all found wanting, but each have contributed to our understanding of the working of the mind. There have been a large number through the ages but there is a trace of each one in the way we talk about memory today. I am going to attempt to summarise them here in a list.

Plato: writing on a wax tablet. Good wax (smooth, deep and the right impressionability) corresponds to a good memory.

Socrates: memory is an aviary. Possessing knowledge is having birds in the aviary.

Augustine: Memories come in through the doorways of the senses and are stored in a treasure house in corridors and passages - images with images, sounds with sounds, smells with smells. Some of these are present from birth.

Middle ages: memory is a library - combined the 'writing' idea of a wax tablet and the storage idea of a treasure house.

Hooke (17th cent): Recently discovered property of phosphorescence used as a metaphor for brain's ability to absorb and store light impressions. Ideas were summoned up by the soul and stored as memories in the microcosm of the brain - where the soul irradiated them - the recent memories closer to the light and thus remembered more clearly than the more ancient ones.

NB It was at Hooke's time that the use of metaphors in science were first derided by the Royal Society. Viewed as 'tricks'.

Around this time Cartesians came to the fore - man as machine from Descartes and memory part of this machine. Babbage produced calculating machine.

Carus - discover of the unconscious and a romantic (18th and early 19th century): Images and sounds are constantly projected into the mind and memory preserves them in a vast labyrinth which is also like a vast loom with a master weaver causing the bobbin to flash back and forth using threads. External appearance reflected the internal workings of the mind.

19th century: metaphors from a range of new discoveries and inventions used.
memory as a switchboard of a telephone exchange - reactivation of a trace laid down by experience.
memory as a mechanical piano - replaying sound laid in to the machine
memory as a phonograph - reproducing sound recorded in wax.
memory as a camera obscurer - like the images striking the soul and changing.
memory as photography. Retains scene and forgets nothing.

Ebbinghaus 1880: memory associations are threads spread out - with strength of memory corresponding ti the distance between them.

Mid-twentieth century development of computer. Computer metaphor for human mind. Produced lots of analogous terminology which were exchanged with psychology and continues to be widely used e.g. memory back-up. Genrally used as metaphor for higher functions - thinking, reasoning and problem-solving.

Post 1970: Hologram metaphor.
Gives good analogy for the vast storage in the brain and the distribution of storage.
Valuable metaphor for describing 'deja vu' (present image too similar to previous image) and 'tip of the tongue' phenomena (ghost images in hologram).

1980s Connectivist metaphor (Brain metaphor) . Calculations based on neural networks (networks imitating the action of a network of neurons communicating with each other).
Good to explain how mind makes matches between different objects of the same class but different in detail.
The system reaches an equilibrium so that white noise has little effect - as in mind.
Damaging the system has little effect on both mind and neural network.
Both content-addressable.
Neural network capable of producing a prototype has been made - as in mind.

The last chapter dealt with the problem of the homunculus - which originally meant an artificial human being.

In psychology the homunculus has become something else: if a theory appeals to the same process which it seeks to explain then it is said to contain a homonculous. What controls the machine of Descartes, the functions of the network, the images of the hologram or the beam of light in Hooke's microcosm? I suppose it could be the soul or God or some superior being. In popular science (and in the comics I read as a child) it is the little man drawn inside the head. It (or he) is required in each theory. So psychology without the homoncular is impossible. It causes each metaphor, in the end, to fail.

No metaphor can provide the answer to what ultimately controls and initiates the metaphor. That is the most interesting question of them all - and , as yet, there is no answer.