What determines the speed of speech recognition? Evidence from congenitally blind adults

It is a matter of debate, whether and how improved auditory discrimination abilities enable speeded speech comprehension in congenitally blind adults. Previous research has concentrated on semantic and syntactic aspects of processing. Here we investigated phonologically mediated spoken word access processes by means of word onset priming. Blind adults and age- and gender-matched sighted adults listened to spoken word onsets (primes) followed by complete words (targets). Phonological overlap between primes and targets varied. Blind participants made faster lexical decision responses than sighted participants, yet their speeded responses were not restricted to phonologically overlapping trials. Furthermore, timing of Event Related Potential (ERP) results did not differ between blind and sighted participants. Together these results suggest that blind and sighted listeners are equally fast in implicit phonological encoding and lexical matching mechanisms. It appears that blind adults' speeded speech processing emerges when phonological analysis makes promising word candidates available for further processing. As one possible interpretation, we speculate that lexical selection processes in blind adults do not need to wait for information from the visual domain, while auditory-visual integration mechanisms are mandatorily implemented in speech recognition routines of sighted adults.