Visual Influence on Auditory Perception of Vowels by French-Speaking Children and Adults.

Audiovisual interaction in speech perception is well defined in adults. Despite the large body of evidence suggesting that children are also sensitive to visual input, very few empirical studies have been conducted. To further investigate whether visual inputs influence auditory perception of phonemes in preschoolers in the same way as in adults, we conducted an audiovisual identification test. The auditory stimuli (/e/-/ø/ continuum) were presented either in an auditory condition only or simultaneously with a visual presentation of the articulation of the vowel /e/ or /ø/. The results suggest that, although all participants experienced visual influence on auditory perception, substantial individual differences exist in the 5- to 6-year-old group. While additional work is required to confirm this hypothesis, we suggest that auditory and visual systems are developing at that age and that multisensory phonological categorization of the rounding contrast took place only in children whose sensory systems and sensorimotor representations were mature.

Enhanced perception of pitch changes in speech and music in early blind adults.

It is well known that congenitally blind adults have enhanced auditory processing for some tasks. For instance, they show supra-normal capacity to perceive accelerated speech. However, only a few studies have investigated basic auditory processing in this population. In this study, we investigated if pitch processing enhancement in the blind is a domain-general or domain-specific phenomenon, and if pitch processing shares the same properties as in the sighted regarding how scores from different domains are associated. Fifteen congenitally blind adults and fifteen sighted adults participated in the study. We first created a set of personalized native and non-native vowel stimuli using an identification and rating task. Then, an adaptive discrimination paradigm was used to determine the frequency difference limen for pitch direction identification of speech (native and non-native vowels) and non-speech stimuli (musical instruments and pure tones). The results show that the blind participants had better discrimination thresholds than controls for native vowels, music stimuli, and pure tones. Whereas within the blind group, the discrimination thresholds were smaller for musical stimuli than speech stimuli, replicating previous findings in sighted participants, we did not find this effect in the current control group. Further analyses indicate that older sighted participants show higher thresholds for instrument sounds compared to speech sounds. This effect of age was not found in the blind group. Moreover, the scores across domains were not associated to the same extent in the blind as they were in the sighted. In conclusion, in addition to providing further evidence of compensatory auditory mechanisms in early blind individuals, our results point to differences in how auditory processing is modulated in this population.

Repetition suppression for speech processing in the associative occipital and parietal cortex of congenitally blind adults.

In the congenitally blind (CB), sensory deprivation results in cross-modal plasticity, with visual cortical activity observed for various auditory tasks. This reorganization has been associated with enhanced auditory abilities and the recruitment of visual brain areas during sound and language processing. The questions we addressed are whether visual cortical activity might also be observed in CB during passive listening to auditory speech and whether cross-modal plasticity is associated with adaptive differences in neuronal populations compared to sighted individuals (SI). We focused on the neural substrate of vowel processing in CB and SI adults using a repetition suppression (RS) paradigm. RS has been associated with enhanced or accelerated neural processing efficiency and synchronous activity between interacting brain regions. We evaluated whether cortical areas in CB were sensitive to RS during repeated vowel processing and whether there were differences across the two groups. In accordance with previous studies, both groups displayed a RS effect in the posterior temporal cortex. In the blind, however, additional occipital, temporal and parietal cortical regions were associated with predictive processing of repeated vowel sounds. The findings suggest a more expanded role for cross-modal compensatory effects in blind persons during sound and speech processing and a functional transfer of specific adaptive properties across neural regions as a consequence of sensory deprivation at birth.