Recent studies have suggested that parsing of multisensory stimulation for efficient attentional allocation is compromised in older adults (Poliakoff et al., 2006). In our study, we investigated the effiency of multisensory integration as a consequence of ageing. We also explored whether inefficient multisensory perception is associated with impaired actions, such as maintenance of balance and gait. Although the association between unisensory degradation and the incidence of falls has already been shown, it is not known whether the integration between sensory inputs is specifically compromised in fall-prone older adults. Here we assessed multisensory efficiency in three groups of participants, fall prone and non fall prone older adults and young adults, using a well-known sound induced visual illusion (Shams et al., 2000). Age, auditory acuity, visual acuity, contrast sensitivity and cognitive functions (assessed through the Mini Mental State Exam) were balanced across older participants.
In the first experiment the number of beeps and flashes was manipulated to assess both the fission (e.g. 1 flash presented with 2 beeps are perceived as 2 flashes) and the fusion illusion (e.g. 2 flashes presented with 1 beep are perceived as 1 flash). The results showed that fall prone older adults were the only group of participants to experience both kinds of illusions.
In the second experiment we assessed whether the temporal window of integration differs across the three groups. It has been shown that older adults have a more extended window of integration (Diedrich et al., 2008). In the present study we presented 1 flash with 2 beeps and we manipulated the SOA between the two beeps from 30ms to 270ms. We found that older adults in general integrate auditory and visual inputs over longer SOAs than younger adults. Moreover, fall prone older adults integrate auditory and visual inputs over a larger temporal window compared to non fall prone older adults. Our findings suggest that ageing is associated with inefficient unisensory processing from multisensory stimulation and that such inefficient perception may account for impaired actions. These results have significant implication for diagnosis and rehabilitation of fall prone elderly.