Quantification of the Synesthetic Experience with the Visual Evoked Potential

Abstract

Synesthesia describes a condition wherein stimulus information of one type appears to produce sensations not normally associated with that stimulus. Experiencing particular colors when certain letters or numbers are viewed has been termed "color-grapheme synesthesia". Synesthesia is believed to influence perception at a relatively low level and result in altered levels of activation in the visual cortex, among other areas. The visual evoked potential (VEP) is uniquely suited to investigate plausible changes in activity levels in the visual cortex, which has proven useful in investigations into the integrity of the visual system. Coupled with a recent upsurge of Magnetic Resonance Imaging (MRI) research investigating the neural underpinnings of synesthesia, the VEP may help further the current body of literature by helping to quantify the synesthetic experience. Pattern reversal and onset/offset VEPs were recorded from controls and subjects with color-grapheme synesthesia. Synesthesia was self-reported but verified with an online testing battery (see synesthete.org) and synesthetes performed color matches to achromatic block letters and symbols. Inducing stimuli were constructed of randomly placed block letters which elicited strong synesthetic color fill-in as well as control symbols and letters that did not elicit colors. Control and matching stimuli were also presented with varied saturations of the matched chromaticity. Fourier and waveform components show differences between synesthetes and controls which indicate that the magnitude of the synesthetic percept can be quantified with the VEP.

Meeting abstract presented at VSS 2012