Purpose: The role of vision in speech representation was investigated in congenitally blind speakers and sighted speakers by studying the correlates of contrastive focus, a prosodic condition in which phonemic contrasts are enhanced. It has been reported that the lips (visible articulators) are less involved in implementing the rounding feature for blind speakers. If the weight of visible gestures in speech representation is reduced in blind speakers, they should show different strategies to mark focus-induced prominence.
Method: Nine congenitally blind French speakers and 9 sighted French speakers were recorded while uttering sentences in neutral and contrastive focus conditions. Internal lip area, upper lip protrusion, and acoustic values (formants, fundamental frequency, duration, and intensity) were measured.
Results: In the acoustic domain, both groups signaled focus by using comparable values of fundamental frequency, intensity, and duration. Formant values in sighted speakers were more affected by the prosodic condition. In the articulatory domain, sighted speakers significantly altered lip geometry in the contrastive focus condition compared with the neutral condition, whereas blind speakers did not.
Conclusion: These results suggest that implementation of prosodic focus is affected by congenital visual deprivation. The authors discuss how these findings can be interpreted in the framework of the perception-for-action-control theory.