Beyond the subjective experience of colour: An experimental case study of grapheme-texture synesthesia

This study was a case investigation of grapheme-texture synestheste TH, a female who subjectively reported experiencing a visual association between grapheme and colour/texture. First, we validated the existence of a synesthetic association in an objective manner. Involuntarily elicited experience is a major hallmark that is common to different types of synesthetes. Our results indicated interference between physical and synesthetic texture, suggesting the involuntary occurrence of synesthetic textural experience. We analysed the behavioural measures using the EZ diffusion model. The result suggested that TH's synesthetic experience was dissociable from that of briefly trained associative processing of non-synesthetes. Second, we investigated how the synesthetic experience of colour and texture dimensions was bound in the visual representation. We found that the interference effects of colour and texture were not independent. This suggested that in the elicited experience, the colour and texture features construct an integrated representation.