Abstract
This investigation examined age-related differences in auditory-visual (AV) integration as reflected on perceptual judgments of temporally misaligned AV English sentences spoken by native English and native Spanish talkers. In the detection task, it was expected that slowed auditory temporal processing of older participants, relative to younger participants, would be manifest as a shift in the range over which participants would judge asynchronous stimuli as synchronous (referred to as the “AV simultaneity window”). The older participants were also expected to exhibit greater declines in speech recognition for asynchronous AV stimuli than younger participants. Talker accent was hypothesized to influence listener performance, with older listeners exhibiting a greater narrowing of the AV simultaneity window and much poorer recognition of asynchronous AV foreign-accented speech compared to younger listeners. Participant groups included younger and older participants with normal hearing and older participants with hearing loss. Stimuli were video recordings of sentences produced by native English and native Spanish talkers. The video recordings were altered in 50 ms steps by delaying either the audio or video onset. Participants performed a detection task in which they judged whether the sentences were synchronous or asynchronous, and performed a recognition task for multiple synchronous and asynchronous conditions. Both the detection and recognition tasks were conducted at the individualized signal-to-noise ratio (SNR) corresponding to approximately 70% correct speech recognition performance for synchronous AV sentences. Older listeners with and without hearing loss generally showed wider AV simultaneity windows than younger listeners, possibly reflecting slowed auditory temporal processing in auditory lead conditions and reduced sensitivity to asynchrony in auditory lag conditions. However, older and younger listeners were affected similarly by misalignment of auditory and visual signal onsets on the speech recognition task. This suggests that older listeners are negatively impacted by temporal misalignments for speech recognition, even when they do not notice that the stimuli are asynchronous. Overall, the findings show that when listener performance is equated for simultaneous AV speech signals, age effects are apparent in detection judgments but not in recognition of asynchronous speech.
Highlights
Everyday speech recognition tasks stimulate both audition and vision
Older listeners are less sensitive to auditory lead asynchronies and perceive wider ranges of AV asynchronous sentences as synchronous, especially for NE talkers
The AV simultaneity window determined from detection judgments was wider for NE talkers than NS talkers by older listeners, there were no differences in recognition performance for NE and NS talkers across a broad range of AV asynchronies
Summary
Everyday speech recognition tasks stimulate both audition and vision. Auditory and visual features of speech stimuli are complementary to each other, and provide some redundancy, both of which enhance a listener’s understanding of the speech signal and underscore the importance of accurate integration. Auditory-visual (AV) integration for speech signals is aided at multiple stages of processing by the listener’s knowledge of the language, as well as by the availability of contextual cues. Working memory aids prediction about the spoken message as it unfolds over time, attention enables the listener to focus on the target message and ignore irrelevant information, and processing speed assists the listener in rapidly integrating, recognizing, and responding to a spoken message. [The reader is referred to Peelle and Sommers (2015), which proposes a dynamic process of AV integration consisting of early and later integration mechanisms in auditory cortex and posterior superior temporal sulcus, based on neurophysiological evidence]
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