Using Race Model Violation to Explore Multisensory Responses in Older Adults: Enhanced Multisensory Integration or Slower Unisensory Processing?

Older adults exhibit greater multisensory reaction time (RT) facilitation than young adults. Since older adults exhibit greater violation of the race model (i.e., cumulative distribution functions for multisensory RTs are greater than that of the summed unisensory RTs), this has been attributed to enhanced multisensory integration. Here we explored whether (a) individual differences in RT distributions within each age group might drive this effect, and (b) the race model is more likely to be violated if unisensory RTs are slower. Young (n = 34) and older adults (n = 30) made speeded responses to visual, auditory or tactile stimuli, or any combination of these (bi-/tri-modal). The test of the race model suggested greater audiovisual integration for older adults, but only when accounting for individual differences in RT distributions. Moreover, correlations in both age groups showed that slower unisensory RTs were associated with a greater degree of race model violation. Therefore, greater race model violation may be due to greater ‘room for improvement’ from unisensory responses in older adults compared to young adults, and thus could falsely give the impression of enhanced multisensory integration.