From A.R. Luria’s The Mind of a Mnemonist

The Mind of a Mnemonist is about an otherwise ordinary man, S., with an extreme eidetic memory, able to remember completely random strings of numbers and characters for years on end. Though he sometimes omits items in the sequences, he never misremembers or falsely adds one, as he seems to have intuitively developed a memory palace technique based on overwhelming synaesthetic associations. If he misses an item, it’s because it was quite literally overlooked in the visual framework. Here he is explaining how he “overlooked” some words in a list while repeating them:

I put the image of the pencil near a fence .. . the one
down the street, you know. But what happened was
that the image fused with that of the fence and I walked
right on past without noticing it. The same thing happened with the word egg. I had put it up against a
white wall and it blended in with the background. How
could I possibly spot a white egg up against a white
wall? Now take the word blimp. That’s something gray,
so it blended in with the gray of the pavement . . .
Banner, of course, means the Red Banner. But, you
know, the building which houses the Moscow City
Soviet of Workers’ Deputies is also red, and since I’d
put the banner close to one of the walls of the building
I just walked on without seeing it.. . Then there’s the
word putamen. I don’t know what this means, but it’s
such a dark word that I couldn’t see it . . . and, be-
sides, the street lamp was quite a distance away . . .

The cost of his prodigious memory is a verbal literalism that incapacitates his ability to appreciate nuance, abstraction, or multiple meanings. Each word only had one concrete, visual meaning summoned up by his mind immediately upon seeing it. Here he is tripping over some lines from Pasternak:

[It] Smiled at a bird-cherry tree, sobbed, drenched
The lacquer of cabs, the tremor of trees . . .*
  Boris Pasternak

He smiled at a bird-cherry tree. This called up an image
of a young man. Then I realized this was taking place
on the Metinskaya in Rezhitsa .. . He smiled at it. But
right after that there’s the word sobbed. That is, tears
have appeared and are wetting it . . . it means the
lines have to do with grief .. . I remembered how some
woman went to the crematorium and sat there for hours
looking at a portrait. . . That expression the lacquer of
cabs—it’s the lady of the manor driving by in her car-
riage from the mill at Yuzhatov. I look on. What is
she doing? She’s looking out of the carriage, trying to
see what’s wrong there. Why is “he” sad? . . . Then
there’s the expression the tremor of trees [word order
reversed in the Russian]. I can see the tremor and then
the trees, but when the words are reversed like this, I
see a tree and have to make it sway back and forth
to understand the phrase itself. This means a lot of
work for me.

[* The verbs are all in the past tense, masculine singular, but
they apply to rain; it is the spring rain Pasternak ascribes
human emotions to. S. interpreted the content and endings
of the verbs as the action of a masculine subject, whereas the
subject was masculine in a purely grammatical sense. [Tr.]]

So to make space for all of the visual associations that are forced upon him with every word, character, and number, S. lost some other kind of internal mental representation, something that allows for abstraction, metaphor, analogy, and indeterminacy. S. was forever unable to grasp the concept of “infinity”:

. . . Infinity—that means what has always been. But
what came before this? What is to follow? No, it’s impossible to see this . . .

In order for me to grasp the meaning of a thing, I
have to see it. . . Take the word nothing. I read it and
thought it must be very profound. I thought it would
be better to call nothing something . . . for I see this
nothing and it is something . . . If I’m to understand
any meaning that is fairly deep, I have to get an image
of it right away. So I turned to my wife and asked
her what nothing meant. But it was so clear to her
that she simply said: “Nothing means there is nothing.”
I understood it differently. I saw this nothing and felt
she must be wrong. The logic we use, for example. It’s
been worked out on the basis of years of experience.
I can see how it has developed, and what it means to
me is that one has to rely on his own sensations of
things. If nothing can appear to a person, that means
it is something. That’s where the trouble comes in . . .

It’s his sensations, and his inability to evade recollection of them in association with any sort of discourse, that disconnect him from many modes of speaking. Though he was able to be social, I imagine he was in some ways cut off from other people, because he could only ever think that they were talking about one thing in particular with each word or phrase, and if words were to be used in different ways, he would be immediately estranged from such a use. By relying on his own sensations, his language is more private than that of other people. Abstraction is more social than sensation.

[Another Russian note: It’s now thought that famous synaesthete Alexander Scriabin was in fact not synaesthetic, as real synaesthetics such as Messiaen do not have synaesthetic associations that map so neatly onto the western scale.]