Effects of aging on audio-visual speech integration.

This study investigated the impact of aging on audio-visual speech integration. A syllable identification task was presented in auditory-only, visual-only, and audio-visual congruent and incongruent conditions. Visual cues were either degraded or unmodified. Stimuli were embedded in stationary noise alternating with modulated noise. Fifteen young adults and 15 older adults participated in this study. Results showed that older adults had preserved lipreading abilities when the visual input was clear but not when it was degraded. The impact of aging on audio-visual integration also depended on the quality of the visual cues. In the visual clear condition, the audio-visual gain was similar in both groups and analyses in the framework of the fuzzy-logical model of perception confirmed that older adults did not differ from younger adults in their audio-visual integration abilities. In the visual reduction condition, the audio-visual gain was reduced in the older group, but only when the noise was stationary, suggesting that older participants could compensate for the loss of lipreading abilities by using the auditory information available in the valleys of the noise. The fuzzy-logical model of perception confirmed the significant impact of aging on audio-visual integration by showing an increased weight of audition in the older group.

Atypical audio-visual speech perception and McGurk effects in children with specific language impairment.

Audiovisual speech perception of children with specific language impairment (SLI) and children with typical language development (TLD) was compared in two experiments using /aCa/ syllables presented in the context of a masking release paradigm. Children had to repeat syllables presented in auditory alone, visual alone (speechreading), audiovisual congruent and incongruent (McGurk) conditions. Stimuli were masked by either stationary (ST) or amplitude modulated (AM) noise. Although children with SLI were less accurate in auditory and audiovisual speech perception, they showed similar auditory masking release effect than children with TLD. Children with SLI also had less correct responses in speechreading than children with TLD, indicating impairment in phonemic processing of visual speech information. In response to McGurk stimuli, children with TLD showed more fusions in AM noise than in ST noise, a consequence of the auditory masking release effect and of the influence of visual information. Children with SLI did not show this effect systematically, suggesting they were less influenced by visual speech. However, when the visual cues were easily identified, the profile of responses to McGurk stimuli was similar in both groups, suggesting that children with SLI do not suffer from an impairment of audiovisual integration. An analysis of percent of information transmitted revealed a deficit in the children with SLI, particularly for the place of articulation feature. Taken together, the data support the hypothesis of an intact peripheral processing of auditory speech information, coupled with a supra modal deficit of phonemic categorization in children with SLI. Clinical implications are discussed.

Degradation of labial information modifies audiovisual speech perception in cochlear-implanted children.

OBJECTIVE: The aim of the present study was to examine audiovisual speech integration in cochlear-implanted children and in normally hearing children exposed to degraded auditory stimuli. Previous studies have shown that speech perception in cochlear-implanted users is biased toward the visual modality when audition and vision provide conflicting information. Our main question was whether an experimentally designed degradation of the visual speech cue would increase the importance of audition in the response pattern. The impact of auditory proficiency was also investigated. DESIGN: A group of 31 children with cochlear implants and a group of 31 normally hearing children matched for chronological age were recruited. All children with cochlear implants had profound congenital deafness and had used their implants for at least 2 years. Participants had to perform an /aCa/ consonant-identification task in which stimuli were presented randomly in three conditions: auditory only, visual only, and audiovisual (congruent and incongruent McGurk stimuli). In half of the experiment, the visual speech cue was normal; in the other half (visual reduction) a degraded visual signal was presented, aimed at preventing lipreading of good quality. The normally hearing children received a spectrally reduced speech signal (simulating the input delivered by the cochlear implant). RESULTS: First, performance in visual-only and in congruent audiovisual modalities were decreased, showing that the visual reduction technique used here was efficient at degrading lipreading. Second, in the incongruent audiovisual trials, visual reduction led to a major increase in the number of auditory based responses in both groups. Differences between proficient and nonproficient children were found in both groups, with nonproficient children's responses being more visual and less auditory than those of proficient children. Further analysis revealed that differences between visually clear and visually reduced conditions and between groups were not only because of differences in unisensory perception but also because of differences in the process of audiovisual integration per se. CONCLUSION: Visual reduction led to an increase in the weight of audition, even in cochlear-implanted children, whose perception is generally dominated by vision. This result suggests that the natural bias in favor of vision is not immutable. Audiovisual speech integration partly depends on the experimental situation, which modulates the informational content of the sensory channels and the weight that is awarded to each of them. Consequently, participants, whether deaf with cochlear implants or having normal hearing, not only base their perception on the most reliable modality but also award it an additional weight.