readings> photographic memory
Every evening at homework time it's the same old struggle with
tables and spellings. The kids learnt them last night. Now they have to
be learnt all over again. Nothing seems to stick. It's doubly strange
as, like most children, they have an extraordinarily memory for
everyday life. Reminded of some random outing even years ago and they
can recall precisely what they were wearing, what they ate, every
trivial detail.
Children's memories are undoubtedly different. One long-standing
neurodevelopmental puzzle is eidetic imagery, or so-called photographic
memory. The ability is fairly common in children but becomes
vanishingly rare in adults. An eidetic image is like having a picture
before the eyes.
Subjects are tested by showing them a photo of a
street scene or an illustration from Alice in Wonderland for about half
a minute. It's best if they scan the target carefully but don't try too
hard to pick out particular details. Then they are asked to project a
mental image onto a blank surface. Successful eidetikers can do this
even after an interval of some minutes. And the memories are so vivid
that they will be able to count the stripes on the Cheshire Cat's tail
or read the number plates of cars in the street scene.
One of the most celebrated cases was that of "Elizabeth", a 23 year old
language student and talented artist who was unusual in being an adult
eidetiker. Elizabeth was tested with random dot stereograms in which a
different pattern of scrambled dots is presented to each eye. When such
a stereogram is fused by binocular vision, a 3D image of something like
a square or the letter T is revealed floating above the page. It was
reported in Nature (Stromeyer and Psotka, Nature, 1970)
that Elizabeth could look at half the stereogram one day and then use
her eidetic powers to project it onto the other half up to three days
later!
Elizabeth's abilities suggest there was something fascinatingly unique
about her brain. Unfortunately there were never any follow-up studies
to find out just what. Rumour has it she was the wife of an eidetic
imagery researcher and found the attention just too embarrassing.
Nevertheless, her story did prompt a more careful study of eidetics and
it was shown that reasonably persistent imagery - of the order of
minutes - was present in about one-in-20 children. The surprise was
that there seemed no particular pattern to the kids who had it.
Eidetic ability did not relate to IQ, educational level, or any other
cognitive variable. Nor did its prevalence change with age. If you had
it as a young child, you still had it as an older child. It was only at
puberty that eidetic imagery suddenly vanished, leaving very few adults
with the ability.
The study of eidetic imagery fell from favour in the 1980s. But recent
research seems to give the glimmer of a neurodevelopmental explanation.
One early theory was that the learning of language and a resulting
shift to a more verbal conceptual style might erode a "primitive"
childhood capacity for imagery. However now it is felt the loss of
eidetic imagery may be due to changes in the neural circuitry
underlying the habits of attention.
Psychologists have shown that our perception of the world is a mix of
bottom-up and top-down processing. The bottom-up activity binds
together the sensory elements - James's blooming, buzzing, confusion.
Top-down attentional effects then act to filter this perceptual state.
In adults, the brain perceives in an educated way, emphasising only the
essential and suppressing both awareness and memory for unnecessary
background details. The theory is that children have a much less
developed ability to filter the world in terms of personal meanings and
so have a rawer perceptual response. Eidetic imagery would be just an
extreme example of leaving the background detail intact. The whole
scene could then linger a few minutes in working memory.
This leaves the question of why the apparently abrupt loss of eidetic
powers at puberty? Well, recent brain scan studies have shown that both
the prefrontal and parietal cortex - precisely the regions associated
with the top-down attentional focusing effects - undergo a phase of
synaptic sprouting and pruning at this age. So perhaps the cortical
pathways needed to exert a strong attentional constraint on perception
only mature right at the end of childhood.
None of this helps with teaching my kids to spell or memorise tables.
But it does explain the nagging memory I have that the sights and
sounds of my own childhood were somehow more
intense, more brightly lit. Neuroscience may soon prove that in your
early years the world really is shiny and new, the colours brighter,
the edges razor-sharp, every detail rendered with unforgettable
vividness. So I say, kids enjoy the spectacle while you can.
Further reading:
Haber RN. Eidetic images. Scientific American, 220:36-44 (1969).
Haber RN. Twenty years of haunting eidetic imagery: Where's the ghost?
Behavioral & Brain Sciences, 2:583-629 (1979).
Wolfe JM. Where is eidetic imagery? Speculations on its psychophysical
and
neurophysiological locus. In The exceptional brain: Neuropsychology of
talent and special
abilities, eds Obler LK and Fein D, Guilford Press (1988).
Gray CR and Gummerman K. The enigmatic eidetic image: A critical
examination of methods, data, and theories. Psychological Bulletin,
82:383-407 (1975).
Giray E et al. A lifespan approach to the study of eidetic imagery.
Journal of Mental, 9:21-32. (1985).
Janesch E. Eidetic Imagery, Harcourt Brace (1930)