"Love looks not with the eyes": supranormal processing of emotional speech in individuals with late-blindness versus preserved processing in individuals with congenital-blindness.

Abstract

Processing of emotional speech in the absence of visual information relies on two auditory channels: semantics and prosody. No study to date has investigated how blindness impacts this process. Two theories, Perceptual Deficit, and Sensory Compensation, yiled different expectations about the role of visual experience (or its lack thereof) in processing emotional speech. To test the effect of vision and early visual experience on processing of emotional speech, we compared individuals with congenital blindness (CB, n = 17), individuals with late blindness (LB, n = 15), and sighted controls (SC, n = 21) on identification and selective-attention of semantic and prosodic spoken-emotions. Results showed that individuals with blindness performed at least as well as SC, supporting Sensory Compensation and the role of cortical reorganisation. Individuals with LB outperformed individuals with CB, in accordance with Perceptual Deficit, supporting the role of early visual experience. The LB advantage was moderated by executive functions (working-memory). Namely, the advantage was erased for individuals with CB who showed higher levels of executive functions. Results suggest that vision is not necessary for processing of emotional speech, but early visual experience could improve it. The findings support a combination of the two aforementioned theories and reject a dichotomous view of deficiencies/enhancements of blindness.