Effects of stimulus complexity on bisensory audiovisual integration

With the rapid increase in the number of elderly people, the number of people with dementia is also increasing. The most common form of dementia is Alzheimer's disease, which accounts for 50-70% of all dementia cases. Until the present time, however, there was no effective early detection method for Alzheimer's disease. A recent study showed that brain glucose metabolism in healthy volunteers was different than glucose metabolism in Alzheimer's patients during the response to passive audiovisual stimulation. This result suggested that the mechanism of audiovisual integration in patients with Alzheimer's disease was influenced by the disease. In the present study, the authors investigated the effects of modality-specific selective attention on audiovisual integration using simple visual and auditory stimuli in healthy human subjects. Three different attentional instructions were accessed: (1) visual selective attention, in which subjects were instructed to focus their attention on visual stimuli; (2) auditory selective attention, in which subjects were instructed to focus their attention on auditory stimuli; and (3) audiovisual divided attention, in which subjects were instructed to focus their attention on both visual and auditory stimuli. The results showed that significant bimodal enhancement was present only in the divided attention condition, which is similar to the results of a previous study using complex semantic stimuli. Therefore, the authors conclude that stimulus complexity does not influence the modality-specific selective attention effects of audiovisual integration. A future study will examine the mechanism of audiovisual integration in patients with Alzheimer's disease using the same experimental design (using simple stimuli), which will hopefully help find a new method for the early detection of Alzheimer's disease.