Measures of auditory-visual integration in nonsense syllables and sentences

For all but the most profoundly hearing-impaired (HI) individuals, auditory-visual (AV) speech has been shown consistently to afford more accurate recognition than auditory (A) or visual (V) speech. However, the amount of AV benefit achieved (i.e., the superiority of AV performance in relation to unimodal performance) can differ widely across HI individuals. To begin to explain these individual differences, several factors need to be considered. The most obvious of these are deficient A and V speech recognition skills. However, large differences in individuals' AV recognition scores persist even when unimodal skill levels are taken into account. These remaining differences might be attributable to differing efficiency in the operation of a perceptual process that integrates A and V speech information. There is at present no accepted measure of the putative integration process. In this study, several possible integration measures are compared using both congruent and discrepant AV nonsense syllable and sentence recognition tasks. Correlations were tested among the integration measures, and between each integration measure and independent measures of AV benefit for nonsense syllables and sentences in noise. Integration measures derived from tests using nonsense syllables were significantly correlated with each other; on these measures, HI subjects show generally high levels of integration ability. Integration measures derived from sentence recognition tests were also significantly correlated with each other, but were not significantly correlated with the measures derived from nonsense syllable tests. Similarly, the measures of AV benefit based on nonsense syllable recognition tests were found not to be significantly correlated with the benefit measures based on tests involving sentence materials. Finally, there were significant correlations between AV integration and benefit measures derived from the same class of speech materials, but nonsignificant correlations between integration and benefit measures derived from different classes of materials. These results suggest that the perceptual processes underlying AV benefit and the integration of A and V speech information might not operate in the same way on nonsense syllable and sentence input.