Abstract
We describe a case study of C, an alphanumeric-colour synaesthete, who has an extraordinary memory for digits. When C views a black digit, it elicits a highly specific colour (i.e., photism) that is experienced as an overlay which conforms to the shape of the digit. In an initial experiment, we evaluated how C's synaesthetic photisms influence her immediate and delayed recall of digits. C and seven non-synaesthetes were presented with three matrices of 50 digits. One matrix consisted of black digits, and two matrices consisted of colored digits. One matrix of colored digits contained digits that were colored to be congruent with C's photisms for the digits, whereas the other matrix of colored digits contained digits that were colored to be incongruent with C's photisms for the digits. The results showed that C's immediate recall of the incongruently colored digits was considerably poorer than her recall of either the black or the congruently colored digits. Similar differences in the recall of the digits from the three matrices were not shown by any of the seven non-synaesthetes. Furthermore, when immediate and delayed (48 hours) recall of the black digits was compared, C showed no decrease in recall over time, whereas each of the non-synaesthetes showed a significant decrease in recall over time. In a subsequent experiment, we sought to rule out the possibility that C's superior delayed recall of the black digits simply reflected a general, above average memory ability. In this experiment, C and seven non-synaesthetes were presented with matrices of shapes that do not elicit color experiences for C. The results showed that unlike her superior delayed recall of black digits, C's delayed recall of shapes was no different than the delayed recall of the non-synaesthetes. Taken together, the findings clearly demonstrate C's extraordinary memory for digits and show that C's synaesthetic photisms influence her immediate and delayed recall of digits.
This research was supported by the Natural Sciences and Engineering Research Council of Canada.