Search for the neural correlates of visual awareness and voluntary control over visual awareness using multivariate fMRI.

Bistable stimuli are a useful tool in the study of visual awareness, because these stimuli allow changes in perceptual state without any change in the actual visual input. In this way, processes related to visual awareness can be isolated. In the present study a bistable rotating sphere was used. This sphere is perceived as rotating either clockwise or counter-clockwise. Changes in perceptual state occur spontaneously, but can also be initiated or inhibited voluntarily. The aim of this study is to find brain activity, measured with fMRI, that represents visual awareness and voluntary control over visual awareness. Subjects were instructed to voluntarily control their perceptual state as good as possible and report, at the same time, their actual perceptual state (clockwise or counter-clockwise rotation). The fMRI data will be analyzed using multivariate pattern-recognition algorithms. These algorithms will be trained to recognize brain activity related to either the actual perceptual state or the wanted perceptual state. Contrary to conventional fMRI analysis techniques that heavily rely on averaging, this technique makes use of percept-selective biases in the activity of individual voxels. Previous work of our lab (Brouwer and Van Ee, 2007) indicated that pattern-recognition algorithms can accurately predict the actual perceptual state of the bistable sphere based on activation patterns of voxels in retinotopic visual cortex, MT+ and parietal cortex. This demonstrates that activity within these visual areas represents actual perceptual state. We now plan on extending this work, determining whether we can find activation patterns related not to the actual perceptual state, but to the wanted perceptual state. In this way we can infer upon the brain mechanisms determining which percept is selected to enter visual awareness and the way effort-of-will influences this selection.