Visual field heterogeneity, laterality, and eidetic imagery in synesthesia.

JS was a grapheme-color synesthete in whom numerals and letters of the alphabet consistently evoked colors. In the first set of experiments we showed that the color - in a consistent and reliable manner - was most pronounced in the left visual field and in central vision. In the second experiment we devised a novel test for eidetic imagery and showed that his self-report of enhanced imagery could be verified experimentally. The implications of these findings for the level at which synesthesia occurs, the 'enhanced cross-activation' model, and the mechanisms of visual memory are discussed.