Introduction. Synesthesia is a mixture of senses in which one sense is automatically triggered by another stimulation sense. Studying the cases in grapheme-color synesthetes, it has historically been believed that stimulation was unidirectional; letters induce a sense of colors but colors do not induce a sense of letters. Recently, a few studies have suggested that colors provoke the inducement of numbers (Cohen & Henik, 2006) suggesting the possibility of bidirectional synesthetic percepts. Methods. Here we've examined the possibility of having a bidirectionality effect with letter graphemes. The subjects included in this study were three synesthetes with matched controls. The stimuli consisted of two sets of color patches in which the colors corresponded with the associated letter graphemes of each synesthete. The color patches were presented in two forms: one set created a word (e.i. having red associated with "U" and blue with "P" spelling the word "UP"), and a non-word (e.i. blue patch followed by a red patch spelling the word "PU"). The participants were presented with a series of forced-choice trials and instructed to select the color patches that represented a word. Results. Results revealed a pattern in which that synesthetes performed significantly different from chance, while control participants typically performed at chance, suggesting possible bidirectional synesthetic perception related with letter graphemes.
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