Enhanced multisensory gain in older adults may be a by-product of inverse effectiveness: Evidence from a speeded response-time task.

Older adults experience a greater benefit from multisensory integration than their younger counterparts, but it is unclear why. One hypothesis is that age-related sensory decline weakens unisensory stimulus effectiveness, causing a boost in multisensory gain through inverse effectiveness. Many previous studies present stimuli at the same intensity for both younger and older adults (i.e., stimulus-matched), as opposed to accounting for each participant's unique perceptual ability (i.e., perception-matched). This makes it difficult to discern the source of age-related differences in multisensory gain. As such, we used two experiments to examine whether sensory decline is contributing to age-related differences in multisensory gain. In the first, we presented auditory (pure tones in noise), visual (Gabor patches in noise), and audiovisual stimuli and recorded response times from 31 younger (18-25) and 30 older (55-80) adults. Importantly, all participants were given identical stimuli, with the expectation that older adults would show worse unisensory performance, inducing inverse effectiveness. The second task was identical (younger = 31, older = 34), except stimuli were presented at each participant's 50% detection threshold, identified with an adaptive psychophysical staircase, controlling for any influence of inverse effectiveness. Older adults were found to exhibit greater multisensory gain (as measured by race model violations) on stimulus- but not perception-matched tasks, thus aligning with the principle of inverse effectiveness. That is, when accounting for potential age-related differences in perceptual abilities, older adults no longer experienced greater benefit from multisensory integration. These two experiments together suggest that the age-related increases in multisensory integration previously reported may be in part due to age-related declines in vision and audition. (PsycInfo Database Record (c) 2024 APA, all rights reserved).