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Parkson Leung, Yee Joon Kim, Marcia Grabowecky, Ken A. Paller, Satoru Suzuki; Cross-modal selective attention effects on steady-state visual evoked potentials (SSVEPs). Journal of Vision 2008;8(6):169. doi: 10.1167/8.6.169.
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Our previous results revealed that spatial attention induced synchronization-based response gain in SSVEPs. In that study, the attended and competing stimuli were visual. Here, we investigated whether attentional response gain generalized to cross-modal conditions. Auditory and visual stimuli were presented, and at the beginning of each trial the modality to be attended was indicated. Observers either attempted to detect a brief color change (120 ms) in the visual modality or a brief sound intensity change (100 ms) in the auditory modality. These targets occurred on 10% of the trials. The intensity of the competing auditory stimulus was perceptually matched to that of the visual stimulus, which was a circular grating flickered (16.7 Hz) at the center of the screen (2.7 seconds/trial). We monitored the SSVEPs induced by this stimulus. There were four experimental conditions: attend visual/ignore auditory, ignore visual/attend auditory, attend visual presented alone, or attend auditory presented alone (making auditory and visual attention equally frequent). SSVEPs were analyzed only for non-target trials. To find evidence of attentional response gain, we used three contrasts: near threshold, intermediate, and saturation level. In cross-modal conditions, we found evidence consistent with response gain, in that attentional modulation of SSVEPs was stronger for higher contrast stimuli. SSVEPs for attended visual stimuli were comparable with or without the competing auditory stimulus. In a second experiment, we quantitatively examined cross-modal interference by pairing the highest-contrast visual stimulus with sounds of varying intensities. Overall, SSVEPs diminished as a function of increasing auditory intensity, demonstrating an intensity-dependent cross-modal interference. In summary, the auditory stimulus interfered with visual processing in proportion to its intensity, and visually directed attention boosted SSVEPs consistent with response gain.
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