Abstract
This article aims to investigate whether auditory stimuli in the horizontal plane, particularly originating from behind the participant, affect audiovisual integration by using behavioral and event-related potential (ERP) measurements. In this study, visual stimuli were presented directly in front of the participants, auditory stimuli were presented at one location in an equidistant horizontal plane at the front (0°, the fixation point), right (90°), back (180°), or left (270°) of the participants, and audiovisual stimuli that include both visual stimuli and auditory stimuli originating from one of the four locations were simultaneously presented. These stimuli were presented randomly with equal probability; during this time, participants were asked to attend to the visual stimulus and respond promptly only to visual target stimuli (a unimodal visual target stimulus and the visual target of the audiovisual stimulus). A significant facilitation of reaction times and hit rates was obtained following audiovisual stimulation, irrespective of whether the auditory stimuli were presented in the front or back of the participant. However, no significant interactions were found between visual stimuli and auditory stimuli from the right or left. Two main ERP components related to audiovisual integration were found: first, auditory stimuli from the front location produced an ERP reaction over the right temporal area and right occipital area at approximately 160–200 milliseconds; second, auditory stimuli from the back produced a reaction over the parietal and occipital areas at approximately 360–400 milliseconds. Our results confirmed that audiovisual integration was also elicited, even though auditory stimuli were presented behind the participant, but no integration occurred when auditory stimuli were presented in the right or left spaces, suggesting that the human brain might be particularly sensitive to information received from behind than both sides.
Highlights
In a social environment, many objects and events are often perceived simultaneously via different sensory systems
By comparing the audiovisual integration elicited by the visual stimulus presented at the front location with the auditory stimuli presented at the four horizontal plane locations, we examined whether audiovisual integration can be modulated according to the positions of the auditory stimuli in the horizontal plane, originating from behind the participants
The pairwise comparisons showed that no significant differences in reaction times were found between the bimodal audiovisual stimuli in which auditory stimuli were presented on the left (p = 0.333) or right (p = 0.066) of the participants and the unimodal visual stimuli
Summary
Many objects and events are often perceived simultaneously via different sensory systems. Previous studies have shown that bimodal audiovisual stimuli can be discriminated or detected more accurately and faster than unimodal auditory or visual stimuli presented alone [1,2,3,4]. This facilitative effect is called ‘‘audiovisual integration’’. Discrimination tasks were used to investigate audiovisual integration using target and standard stimuli, and subjects were required to respond only to target stimuli [2,3]. Discrimination tasks involve visual (or auditory) detection methods in which subjects are instructed to respond to visual (or auditory) target stimuli while not responding to standard stimuli [3,5] or visual and auditory detection methods in which subjects are required to respond to both visual and auditory target stimuli [6,7]
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