Synesthesia does not help to recover perceptual dominance following flash suppression

Abstract

Grapheme-color synesthesia is a perceptual phenomenon that occurs when letters or numbers elicit an abnormal color sensation (e.g., printed black letters are perceived as colored graphemes). Grapheme-color synesthesia is typically reported following explicit presentation of graphemes. Very few studies have investigated color sensations in synesthesia in the absence of visual awareness. To address this issue, we took advantage of the dichoptic flash suppression paradigm to temporarily render a stimulus presented to one eye invisible. Synesthesic alphanumeric and non-synesthetic abstract stimuli were presented to 11 synesthete and 11 matched control participants in achromatic and chromatic experimental conditions. The test stimulus was first displayed to one eye and then masked following the sudden presentation of visual noise in the other eye. The time for an image to be perceived following the onset of the suppressive noise was calculated in each condition. Trials free of flash suppression but mimicking the perceptual suppression of the flash were also tested. Results showed that target detection by synesthetes was significantly better than by controls in the absence of flash suppression. However, no statistically significant difference was found between the groups when the test stimulus was interocularly suppressed, either for synesthetic or non-synesthetic stimuli. This study suggests that synesthesia can be associated with enhanced perception for overt recognition, but does not occur in the absence of visual awareness.