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The Contribution of area V5+/hMT+ to the awareness of motion during binocular rivalry

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Zaretskaya, N., & Bartels, A. (2012). The Contribution of area V5+/hMT+ to the awareness of motion during binocular rivalry. Poster presented at 18th Annual Meeting of the Organization for Human Brain Mapping (OHBM 2012), Beijing, China.

Cite as: http://hdl.handle.net/21.11116/0000-0001-9E8C-0
Introduction: Certain areas of the brain are known to be specialized for processing distinct stimulus types. For example, area V5/MT is crucial for processing and perception of visual motion, and regions in the fusiform gyrus (e.g. FFA) are important for processing and perception of faces. When a face is presented to one eye, and visual motion to the other, conscious perception alternates between the two in a random sequence, such that only one of the two is perceived and the other suppressed (a process termed binocular rivalry). It is an unresolved question whether and how activity in the distinct regions specialized for the stimuli contributes to conscious perception during rivalry. It is known however that stimulus-specific responses in these areas can be observed even when subjects are not aware of the stimulus. Methods: In the current study we investigated the role of motion-processing area V5/MT+ in the awareness of motion and of faces during binocular rivalry. We interfered with ongoing neural activity in V5+/MT+ by means of transcranial magnetic stimulation (TMS) in 12 human subjects while they reported their perceptual alternations between visual motion and a static face stimulus, each presented to a different eye. Results: We found that compared to a control condition in which a neutral site (vertex) was stimulated using TMS, the stimulation of V5+/MT+ did not affect the duration of motion perception periods, but instead lengthened the phases during which the face was perceived (and motion suppressed). Conclusions: The observed effect is equivalent to that when the stimulus-strength of one of the two competing stimuli, in this case visual motion, is weakened (e.g. by reducing contrast, luminance or motion speed) (Levelt, 1966). Our findings suggest that activity in V5+/MT+ contributes to the on-going competition for perceptual dominance in binocular rivalry, and that injecting noise into it has effects similar to those of reducing the stimulus strength of the visual motion display. To our knowledge this is the first direct manipulation of activity in a functionally specialized visual area with consequences on conscious perception during binocular rivalry.