Assessing age-related multisensory enhancement with the time-window-of-integration model.

Although from multisensory research a great deal is known about how the different senses interact, there is little knowledge as to the impact of aging on these multisensory processes. In this study, we measured saccadic reaction time (SRT) of aged and young individuals to the onset of a visual target stimulus with and without an accessory auditory stimulus occurring (focused attention task). The response time pattern for both groups was similar: mean SRT to bimodal stimuli was generally shorter than to unimodal stimuli, and mean bimodal SRT was shorter when the auditory accessory was presented ipsilaterally rather than contralaterally to the target. The elderly participants were considerably slower than the younger participants under all conditions but showed a greater multisensory enhancement, that is, they seem to benefit more from bimodal stimulus presentation. In an attempt to weigh the contributions of peripheral sensory processes relative to more central cognitive processes possibly responsible for the difference in the younger and older adults, the time-window-of-integration (TWIN) model for crossmodal interaction in saccadic eye movements developed by the authors was fitted to the data from both groups. The model parameters suggest that (i) there is a slowing of the peripheral sensory processing in the elderly, (ii) as a result of this slowing, the probability of integration is smaller in the elderly even with a wider time-window-of-integration, and (iii) multisensory integration, if it occurs, manifests itself in larger neural enhancement in the elderly; however, because of (ii), on average the integration effect is not large enough to compensate for the peripheral slowing in the elderly.