Stimulus Onset Asynchrony Affects Weighting-related Event-related Spectral Power in Self-motion Perception.

Self-motion perception relies primarily on the integration of the visual, vestibular, proprioceptive, and somatosensory systems. There is a gap in understanding how a temporal lag between visual and vestibular motion cues affects visual-vestibular weighting during self-motion perception. The beta band is an index of visual-vestibular weighting, in that robust beta event-related synchronization (ERS) is associated with visual weighting bias, and robust beta event-related desynchronization is associated with vestibular weighting bias. The present study examined modulation of event-related spectral power during a heading judgment task in which participants attended to either visual (optic flow) or physical (inertial cues stimulating the vestibular, proprioceptive and somatosensory systems) motion cues from a motion simulator mounted on a MOOG Stewart Platform. The temporal lag between the onset of visual and physical motion cues was manipulated to produce three lag conditions: simultaneous onset, visual before physical motion onset, and physical before visual motion onset. There were two main findings. First, we demonstrated that when the attended motion cue was presented before an ignored cue, the power of beta associated with the attended modality was greater than when visual-vestibular cues were presented simultaneously or when the ignored cue was presented first. This was the case for beta ERS when the visual-motion cue was attended to, and beta event-related desynchronization when the physical-motion cue was attended to. Second, we tested whether the power of feature-binding gamma ERS (demonstrated in audiovisual and visual-tactile integration studies) increased when the visual-vestibular cues were presented simultaneously versus with temporal asynchrony. We did not observe an increase in gamma ERS when cues were presented simultaneously, suggesting that electrophysiological markers of visual-vestibular binding differ from markers of audiovisual and visual-tactile integration. All event-related spectral power reported in this study were generated from dipoles projecting from the left and right motor areas, based on the results of Measure Projection Analysis.

Visual imagery influences attentional guidance during visual search: Behavioral and electrophysiological evidence.

Recent behavioral studies have shown that color imagery can benefit visual search when it is congruent with an upcoming target. In the present study we investigated whether this color imagery benefit was due to the processes underlying attentional guidance, as indicated by the electrophysiological marker known as the N2pc component. Participants were instructed to imagine a color prior to each trial of a singleton search task. On some trials, the imagined color was congruent with the target, and on other trials, it was congruent with the distractors. The analyses revealed that the N2pc was present when color imagery was congruent with the search target, and absent when it was congruent with the distractors. Further, there was preliminary evidence that attentional guidance depended on the vividness of color imagery and the frequency at which participants implemented the imagery instruction. Overall, the results of the present study indicate that color imagery can influence the attentional guidance processes underlying visual search.

Attention modulates event-related spectral power in multisensory self-motion perception.

Humans integrate visual and physical (vestibular and proprioceptive) cues to motion during self-motion perception. Theta and alpha-band oscillations have been associated with the processing of visual motion (e.g. optic flow). Alpha and beta-band oscillations have been shown to be associated with sensory-motor processing (e.g. walking). The present study examined modulation of theta, alpha, and beta oscillations while participants made heading direction judgments during a passive self-motion task which required selective attention to one of the simultaneously presented visual or physical motion stimuli. Attention to physical (while ignoring visual) motion produced a different time course of changes in spectral power compared to attention to visual (while ignoring physical) motion. We observed weaker theta event-related synchronization (ERS), as well as stronger beta and later onset of alpha event-related desynchronization (ERD) in the attend-physical condition compared to the attend-visual condition. We observed individual differences in terms of ability to perform the task. Specifically, some participants were not able to ignore or discount the visual input when visual and physical heading direction was incongruent; this was reflected by similar event-related spectral power for both conditions. The results demonstrated a possible electrophysiological signature of the time course of 1) cue conflict (congruency effects), 2) attention to specific motion cues, and 3) individual differences in perceptual weighting of motion stimuli (high-vs. low-accuracy effects).