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Yu Man Chan, Michael J Pianta, Allison M McKendrick; Does age-related decline in vision and hearing result in difficulties separating visual and auditory signals in time?. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3005.
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To accurately perceive the world, we need to correctly combine visual and auditory signals from the same event. Due to differences in transmission speed in air and in neural processing, visual and auditory signals are often temporally offset when they arrive at a multisensory processing brain area, hence some tolerance to asynchrony is needed. Younger adults perceive asynchrony between visual and auditory signals when the temporal offset exceeds around 300ms. Previous studies report that older adults require larger temporal offsets to perceive such asynchrony. We aimed to determine if this finding can be accounted for by declining vision and hearing with age.
Individual psychometric functions were first obtained in fifteen younger (21-32 years old) and thirteen older (60-72 years old) adults, for visual contrast (Gabor, 10ms, 3c/deg, standard deviation of the Gaussian envelope=0.33deg) and sound detection (10ms tone pip presented over a tone mask (75dB), 2.5ms onset-offset ramp, 0.5 or 4kHz) thresholds. In a two-interval-forced-choice design (one interval contained a synchronous stimulus pair, the other was asynchronous), observers judged which interval contained the asynchronous pair. Four conditions were tested: suprathreshold and near threshold stimulus levels, each tested at 0.5 and 4kHz sound frequency. Window width was taken as the difference between the sound-lead and sound-lag asynchrony detection thresholds.
Mean window widths are shown in the attached table. There was a significant interaction between age and sound frequency on the widths (RM-ANOVA: F(1,26)=4.90, p=0.04). Older adults required a larger temporal offset between suprathreshold visual and auditory signals to perceive asynchrony, but was more evident for low than high frequency sounds (interaction between sound frequency, threshold level and age: F(1,26)=5.32, p=0.03).
In older age, auditory and visual signals that are separated in time are more likely to be perceived as simultaneous. Consequently, older adults are more likely to incorrectly combine unassociated auditory and visual signals. Contrary to the effect expected if presbycusis was a driving factor, this age effect was more evident for low than high frequency sounds.
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