Effects of endogenous spatial attention and exogenous spatial attention on multisensory integration

Attention effect has been greatly explored in multisensory integration. Previous studies found that endogenous spatial attention enhanced multisensory integration, while exogenous spatial attention decreased multisensory integration. However, there is no research integrates two kinds of spatial attention into the multisensory integration. In present study, we used endogenous-exogenous spatial cue target paradigm to investigate the effect of endogenous spatial attention and exogenous spatial attention on multisensory integration. The present study consisted of 2 experiments. In these experiments, we mainly manipulated the endogenous cue validities (including cued, uncued), exogenous cue validities (including cued, uncued) and target modalities (including visual, auditory, and audiovisual modalities). Thirty-six students in Liaoning Normal University were recruited in Exp. 1. The visual (V) target was a white pentagonal asterisk block (2 degrees x2 degrees). The auditory (A) target was a 1 600 Hz sinusoidal tone presented by speakers. The audiovisual (AV) target was composed by the simultaneous presentation of both the visual and the auditory stimuli. At the beginning of each trial, the fixation stimulus was presented for 600 similar to 800 ms in the center of the monitor. Following the fixation stimulus, the endogenous cue was presented for 200 ms, which could predict (80%) the location of the target. Then a visual white square served as a exogenous cue was presented for 200 ms at the left or right location randomly. Before the target that appeared for 100 ms, the inter stimulus interval (ISI) lasted for 150 ms. The target (A, V, or AV) randomly appeared for 100 ms in the left or right locations. At last, the fixation stimuli appeared for 1000 ms to wait for the correspondence responses to targets. During the experiment, the participants were asked to locate targets by pressing buttons (F/J) as quickly and accurately as possible. Thirty-six college students were recruited in Exp. 2. In Exp. 2, visual stimuli included checkerboard squares (3.2 degrees x3.2 degrees) with gray (RGB: 147, 149, 152) in the middle and black (RGB: 0, 0, 0) in the middle; auditory stimuli included high-frequency sinusoidal tone (1400) and low-frequency sinusoidal tone (714). The visual target was one of the above two visual stimuli, and the auditory target was one of the above two auditory stimuli. The pairings of two single channel stimuli constituted audiovisual target. The Exp. 2 consisted of four audiovisual targets. Each set of audiovisual targets were balanced among the subjects. The results showed that the responses to AV targets were faster than V or A targets, indicating the appearance of the bimodal advancement effect in both experiments. In addition, we found exogenous spatial attention's race model (probability difference) showed significant smaller at cued compared to uncued condition in both experiments, while the endogenous spatial attention reduced the extent to which the exogenous spatial attention weakened the effect of multisensory integration in Exp.2, but not in Exp. 1. From the results of the relative amount of multisensory response enhancement (rMRE), In Exp. 1, the effects of endogenous spatial attention and exogenous spatial attention on multisensory integration were marginal significant. In Exp. 2, the two kinds of spatial attention had significant interaction with multisensory integration. In summary, exogenous spatial attention decreased multisensory integration in both experiments. Endogenous spatial attention is involved in multisensory integration and has an impact on exogenous spatial attention in Exp. 2. The effects of endogenous spatial attention and exogenous spatial attention on multisensory integration in an interactive manner.