Although neuronal studies have shown that audiovisual integration is regulated by temporal factors, there is still little knowledge about the impact of temporal factors on audiovisual integration in older adults. To clarify how stimulus onset asynchrony (SOA) between auditory and visual stimuli modulates age-related audiovisual integration, 20 younger adults (21-24 years) and 20 older adults (61-80 years) were instructed to perform an auditory or visual stimuli discrimination experiment. The results showed that in younger adults, audiovisual integration was altered from an enhancement (AV, A ± 50 V) to a depression (A ± 150 V). In older adults, the alterative pattern was similar to that for younger adults with the expansion of SOA; however, older adults showed significantly delayed onset for the time-window-of-integration and peak latency in all conditions, which further demonstrated that audiovisual integration was delayed more severely with the expansion of SOA, especially in the peak latency for V-preceded-A conditions in older adults. Our study suggested that audiovisual facilitative integration occurs only within a certain SOA range (e.g., -50 to 50 ms) in both younger and older adults. Moreover, our results confirm that the response for older adults was slowed and provided empirical evidence that integration ability is much more sensitive to the temporal alignment of audiovisual stimuli in older adults.

Interaction occurs in brain when human gets stimuli from different sensory organs such as visual and auditory ． Previous behavioral studies have shown that bimodal audiovisual stimuli simultaneously can be discriminated or detected more rapidly and accurately than unimodal visual or auditory stimuli presented alone ． Many studies have shown that temporal asynchrony of audio − visua 匡 stimuli can inf 苴 uence the integration between visual and auditory stimulus ， however ， the multisensory mechanisms of asynchrony 量 nputs were not well understood ． In this study ， we measurcd the behavioral and EEG data when the visual and auditoIy stimu ［ i onset asynchrony wcre presented in the screen ． This was done fbr each of the five different 50− ms subranges of stimulus onset asynchrony ． Behavioral results showed that reaction times to the asynchrony audiovisual stimuli werc faster that the unimodal stimulus ． Moreover ， the interaction of the asynchrony input was verified f ｝ om event related potentials ( ERPs ) ， Especially ， the results showed that the effect on EEG component around 200ms was largest when visual was presented after the auditory stimuli． This result suggested that might refieCt the proeessing or adjusting for the temporal alignment ofaudiovisual stimuli ． KePt MordS ： Biomed 孟 cal engineering ， EE ( 廴 Event−related potentials ( ERP ) ， Audiovisual integration

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