Learning, Memory, and Synesthesia Nathan Witthoft and Jonathan Winawer Department of Psychology, Stanford University Abstract People with color-grapheme synesthesia experience color when viewing written letters or numerals, usually with a particular color evoked by each grapheme. Here we report on 11 color- grapheme synesthetes with startlingly similar color-grapheme pairings traceable to childhood toys containing colored letters. These data are the first and only to show learned synesthesia of this kind in a group larger than a single case. While some researchers have focused on genetic and perceptual aspects of synesthesia, these results indicate that a complete explanation of synesthesia must also incorporate a central role for learning and memory. We argue that these two positions can be reconciled by thinking of synesthesia as the automatic retrieval of highly specific mnemonic associations, where perceptual contents are brought to mind, akin to mental imagery or the perceptual reinstatement effects found in the memory literature. Introduction A person is said to have synesthesia when their perception of a physical stimulus, such as this black letter ‘A’, automatically produces an impression which is not ordinarily derived from the stimulus, for example that this ‘A’ is red. Experiencing colors in response to reading achromatic printed letters and numbers (grapheme-color synesthesia) is among the most common and widely studied kinds of synesthesia, (Simner et al., 2006). Other pairings within and between sensory modalities have also been reported, including colors evoked by musical pitches, (Marks, 1975), spatial arrangements elicited by numbers, (Galton, 1881; Calkins, 1893), and tastes in response to words (Ward & Simner, 2003). Over a century ago, Galton (1881) prefaced his description of color-number synesthesia by cautioning readers that the contents of every sane person’s mind are not the same as their own. He was aware that to some, synesthesia appeared implausible, or at best, an anomaly with little relation to the study of ordinary cognition. Since then, many results in psychophysics and neuroimaging have attested to the perceptual and neural basis of synesthesia (Ramachandran & Hubbard, 2001; Kim & Blake, 2005; Blake, Palmeri, Marois, & Kim, 2005; Kim, Blake, & Palmeri, 2006; Hubbard & Ramachandran, 2005; Witthoft & Winawer, 2006). Researchers have argued that synesthesia matters because relationships between ideas or modes of experience, such as pitch and brightness, or space and number that are implicit in the non-synesthete are made explicit in the synesthete, (Marks, 1975; Ramachandran & Hubbard, 2001b; Martino & Marks, 2001; Cohen Kadosh & Henik, 2007), providing an unobscured view of the representations underlying normal cognitive processes like cross-modal perception, abstraction, and metaphor. The idea that grapheme-color synesthetes learn their colors from childhood toys was proposed over a hundred years ago (Calkins, 1893), but documented cases are exceedingly rare. In one large-scale investigation, Rich et al. (2005) compared colored letters and Correspondence concerning this article should be addressed to: Nathan WItthoft, 416 Jordan Hall, Department of Psychology, Stanford University, Stanford, CA, 94305. witthoft@stanford.edu. NIH Public Access Author Manuscript Psychol Sci. Author manuscript; available in PMC 2013 May 09. Published in final edited form as: Psychol Sci. 2013 March 1; 24(3): 258–265. doi:10.1177/0956797612452573. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript