Interference from audio distracters during speechreading

Children's use of spatial and visual cues for release from perceptual masking

This study examined the role of visual speech in providing release from perceptual masking in children by comparing visual speech benefit across conditions with and without a spatial separation cue. Auditory-only and audiovisual speech recognition thresholds in a two-talker speech masker were obtained from 21 children with typical hearing (7-9 years of age) using a color-number identification task. The target was presented from a loudspeaker at 0° azimuth. Masker source location varied across conditions. In the spatially collocated condition, the masker was also presented from the loudspeaker at 0° azimuth. In the spatially separated condition, the masker was presented from the loudspeaker at 0° azimuth and a loudspeaker at -90° azimuth, with the signal from the -90° loudspeaker leading the signal from the 0° loudspeaker by 4 ms. The visual stimulus (static image or video of the target talker) was presented at 0° azimuth. Children achieved better thresholds when the spatial cue was provided and when the visual cue was provided. Visual and spatial cue benefit did not differ significantly depending on the presence of the other cue. Additional studies are needed to characterize how children's preferential use of visual and spatial cues varies depending on the strength of each cue.

Comparison of informational vs. energetic masking effects on speechreading performance

The effects of two types of auditory distracters (steady-state noise vs. four-talker babble) on visual-only speechreading accuracy were tested against a baseline (silence) in 23 participants with above-average speechreading ability. Their task was to speechread high frequency Swedish words. They were asked to rate their own performance and effort, and report how distracting each type of auditory distracter was. Only four-talker babble impeded speechreading accuracy. This suggests competition for phonological processing, since the four-talker babble demands phonological processing, which is also required for the speechreading task. Better accuracy was associated with lower self-rated effort in silence; no other correlations were found.

Binding and unbinding the auditory and visual streams in the McGurk effect

Subjects presented with coherent auditory and visual streams generally fuse them into a single percept. This results in enhanced intelligibility in noise, or in visual modification of the auditory percept in the McGurk effect. It is classically considered that processing is done independently in the auditory and visual systems before interaction occurs at a certain representational stage, resulting in an integrated percept. However, some behavioral and neurophysiological data suggest the existence of a two-stage process. A first stage would involve binding together the appropriate pieces of audio and video information before fusion per se in a second stage. Then it should be possible to design experiments leading to unbinding. It is shown here that if a given McGurk stimulus is preceded by an incoherent audiovisual context, the amount of McGurk effect is largely reduced. Various kinds of incoherent contexts (acoustic syllables dubbed on video sentences or phonetic or temporal modifications of the acoustic content of a regular sequence of audiovisual syllables) can significantly reduce the McGurk effect even when they are short (less than 4 s). The data are interpreted in the framework of a two-stage "binding and fusion" model for audiovisual speech perception.

Individual differences and age effects in a dichotic informational masking paradigm

Sixty normally-hearing listeners, ages 5 to 61 years, participated in a monaural speech understanding task designed to assess the impact of a single-talker speech masker presented to the opposite ear. The speech targets were masked by ipsilateral speech-spectrum noise. Masker level was fixed and target level was varied to estimate psychometric functions. The target/masker ratio that led to 51% correct performance in this task was taken as the baseline threshold. The impact of a modulated speech-spectrum noise, a male talker, or a female talker presented at a fixed level to the contralateral ear was quantified by the change in the baseline threshold and was assumed to reflect informational masking. The modulated-noise masker produced no informational masking across the entire age range. Speech maskers produced as much as 20 dB of informational masking for children aged 5-8 years and only 4 dB for adults. In contrast with previous studies using ipsilateral speech maskers, the male and female contralateral speech maskers produced comparable informational masking. Analyses of the developmental rate of change for informational masking and of the patterns of individual differences suggest that the informational masking produced by contralateral and ipsilateral maskers may be mediated by different mechanisms or processes.

Informational masking of speech in children: auditory-visual integration

The focus of this study was the release from informational masking that could be obtained in a speech task by viewing a video of the target talker. A closed-set speech recognition paradigm was used to measure informational masking in 23 children (ages 6-16 years) and 10 adults. An audio-only condition required attention to a monaural target speech message that was presented to the same ear with a time-synchronized distracter message. In an audiovisual condition, a synchronized video of the target talker was also presented to assess the release from informational masking that could be achieved by speechreading. Children required higher target/distracter ratios than adults to reach comparable performance levels in the audio-only condition, reflecting a greater extent of informational masking in these listeners. There was a monotonic age effect, such that even the children in the oldest age group (12-16.9 years) demonstrated performance somewhat poorer than adults. Older children and adults improved significantly in the audiovisual condition, producing a release from informational masking of 15 dB or more in some adult listeners. Audiovisual presentation produced no informational masking release for the youngest children. Across all ages, the benefit of a synchronized video was strongly associated with speechreading ability.