Synaesthetic photisms influence visual perception

When C, a digit-color synaesthete, views black digits, she reports that eac h digit elicits a highly specific color (a photism), which is experienced a s though the color was externally projected onto the digit. We evaluated th is claim by assessing whether C's photisms influenced her ability to percei ve visually presented digits. C identified and localized target digits pres ented against backgrounds that were either congruent or incongruent with th e color of her photism for the digits. The results showed that C was poorer at identifying and localizing digits on congruent than incongruent trials. Such differences in performance between congruent and incongruent trials w ere not found with nonsynaesthete control participants. These results sugge st that C's colored photisms influence her perception of black digits. We p ropose a model in which color information influences the perception of digi ts through reentrant pathways in the visual system.