Contributions of visual speech, visual distractors, and cognition to speech perception in noise for younger and older adults

Older adults report that understanding speech in noisy situations (e.g., a restaurant) is difficult. Repeated experiences of frustration in noisy situations may cause older adults to withdraw socially, increasing their susceptibility to mental and physical illness. Understanding the factors that contribute to older adults’ difficulty in noise, and in turn, what might be able to alleviate this difficulty, is therefore an important area of research. The experiments in this thesis investigated how sensory and cognitive factors, in particular attention, affect older and younger adults’ ability to understand speech in noise. First, the performance of older as well as younger adults on a standardised speech perception in noise task and on a series of cognitive and hearing tasks was assessed. A correlational analysis indicated that there was no reliable association between pure-tone audiometry and speech perception in noise performance but that there was some evidence of an association between auditory attention and speech perception in noise performance for older adults. Next, a series of experiments were conducted that aimed to investigate the role of attention in gaining a visual speech benefit in noise. These auditory-visual experiments were largely motivated by the idea that as the visual speech benefit is the largest benefit available to listeners in noisy situations, any reduction in this benefit, particularly for older adults, could exacerbate difficulties understanding speech in noise. For the first auditory-visual experiments, whether increasing the number of visual distractors displayed affected the visual speech benefit in noise for younger and older adults when the SNR was -6dB (Experiment 1) and when the SNR was -1dB (Experiment 2) was tested. For both SNRs, the magnitude of older adults’ visual speech benefit reduced by approximately 50% each time an additional visual distractor was presented. Younger adults showed the same pattern when the SNR was - 6dB, but unlike older adults, were able to get a full visual speech benefit when one distractor was presented and the SNR was -1dB. As discussed in Chapter 3, a possible interpretation of these results is that combining auditory and visual speech requires attentional resources. To follow up the finding that visual distractors had a detrimental impact on the visual speech benefit, particularly for older adults, the experiment in Chapter 4 tested whether presenting a salient visual cue that indicated the location of the target talker would help older adults get a visual speech benefit. The results showed that older adults did not benefit from the cue, whereas younger adults did. As older adults should have had sufficient time to switch their gaze and/or attention to the location of the target talker, the failure to find a cueing effect suggests that age related declines in inhibition likely affected older adults’ ability to ignore the visual distractor. The final experiment tested whether the visual speech benefit and the visual distraction effect found for older adults in Chapter 4 transferred to a conversationcomprehension style task (i.e., The Question-and-Answer Task). The results showed that younger and older adults’ performance improved on an auditory-visual condition in comparison to an auditory-only condition and that this benefit did not reduce when a visual distractor was presented. To explain the absence of a distraction effect, several properties of the visual distractor presented were discussed. Together, the experiments in this thesis suggest that the roles of attention and visual distraction should be considered when trying to understand the communication difficulties that older adults experience in noisy situations