Assessment of transient negative affect in synesthesia

Abstract

The purpose of this dissertation was to investigate how synesthesia may influence affect and sensorimotor gating in synesthetes. Synesthesia is the phenomenon in which a sensory experience triggers a conscious perception that is in addition to perceptions most people would experience in response to the stimulus. The type of synesthetic experience involving colors for letters and/or numbers is indicative of grapheme to color synesthesia; the most frequently reported type of synesthesia. For example, a synesthete may report seeing the color green in response to hearing or seeing a particular number or letter. Anecdotal reports by synesthetes describe negative affect when viewing a number or letter in a color that does not match (i.e., is incongruent) the synesthete's automatic perceptions. In addition, many reports by synesthetes indicate a greater propensity for experiencing ―sensory overload‖ than non-synesthetes. It was predicted that briefly viewing an incongruent grapheme would produce a transient negative affective state, temporarily increasing the magnitude of startle reflex as measured by eyeblinks among grapheme -> color synesthetes. Results did not support an interaction effect involving Presence of Synesthesia and Picture Condition, F(2,23) = 1.35, p >.05. Although magnitude of startle was greater for grapheme -> synesthetes than when viewing an incongruent grapheme compared to viewing a congruent grapheme or in the baseline (no picture) condition, these results were not statistically significant. It was also predicted that, when examining sensorimotor gating in synesthetes and non-synesthetes with prepulse inhibition (PPI) as the index, synesthetes would show less PPI, indicating increased sensory overload susceptibility. This hypothesis was not supported. Although synesthetes did not display reduced PPI, significantly more synesthetes than non-synesthetes reported experiencing sensory overload, and significantly higher levels of sensory sensitivity and sensation avoiding.