Shereshevskii participated in many behavioral studies, most of them carried out by the neuropsychologist Alexander Luria over a thirty-year time span. He met Luria after an anecdotal event in which he was told off for not taking any notes while attending a work meeting in the mid-1920s. To the astonishment of everyone there (and to his own astonishment in realising that others could apparently not do so), he could recall the speech word by word. Along the years Shereshevsky was asked to memorize complex mathematical formulas, huge matrices and even poems in foreign languages and did so in a matter of minutes. Despite his astounding memory performance, Shereshevsky scored no better than average in intelligence tests.
On the basis of his studies, Luria diagnosed in Shereshevsky an extremely strong version of synaesthesia, fivefold synaesthesia, in which the stimulation of one of his senses produced a reaction in every other. For example, if Shereshevsky heard a musical tone played he would immediately see a colour, touch would trigger a taste sensation, and so on for each of the senses. The images that his synaesthesia produced usually aided him in memorizing. For example, when thinking about numbers he reported:
Take the number 1. This is a proud, well-built man; 2 is a high-spirited woman; 3 a gloomy person; 6 a man with a swollen foot; 7 a man with a moustache; 8 a very stout woman—a sack within a sack. As for the number 87, what I see is a fat woman and a man twirling his moustache.
The above list of images for digits is consistent with a form of synesthesia (or ideasthesia) known as ordinal linguistic personification but is also related to a well-known mnemonic technique called the number shape system where the mnemonist creates images that physically resemble the digits. Luria did not clearly distinguish between whatever natural ability Shereshevsky might have had and mnemonic techniques like the method of loci and number shapes that "S" described.
He had an active imagination, which helped him generate useful mnemonics. He claimed that his condition often produced unnecessary and distracting images or feelings. He had trouble memorizing information whose intended meaning differed from its literal one, as well as trouble recognizing faces, which he saw as "very changeable". He also occasionally had problems reading, because the written words evoked distracting sensations. Things were far worse when he, for example, ate while reading. An example of the difficulties he faced in daily life:
One time I went to buy some ice cream ... I walked over to the vendor and asked her what kind of ice cream she had. 'Fruit ice cream,' she said. But she answered in such a tone that a whole pile of coals, of black cinders, came bursting out of her mouth, and I couldn't bring myself to buy any ice cream after she had answered in that way ...
His memories were so strong that he could recall them after many years. After he discovered his own abilities, he performed as a mnemonist; but this created confusion in his mind. He went as far as writing things down on paper and burning it, so that he could see the words in cinders, in a desperate attempt to forget them, though some mnemonists have speculated that this could have been a mentalist's technique for writing things down to later commit to long-term memory. Reportedly, in his late years, he realized that he could forget facts with just a conscious desire to remove them from his memory, although Luria did not test this directly.
- Away with Words: a film by Christopher Doyle largely inspired by Luria's descriptions of Shereshevskii's life
- Luria, Aleksandr Romanovich (1987). The mind of a mnemonist: a little book about a vast memory. Cambridge: Harvard University Press. ISBN 0-674-57622-5.
- Luria, Aleksandr Romanovich; Lurii︠a︡, A. R. (1987). The mind of a mnemonist: a little book about a vast memory. Cambridge: Harvard University Press. p. 31. ISBN 0-674-57622-5.
- Luria, Aleksandr Romanovich; Lurii︠a︡, A. R. (1987). The mind of a mnemonist: a little book about a vast memory. Cambridge: Harvard University Press. p. 82. ISBN 0-674-57622-5.
- Savantism and Memory Competitions