Neuropsychological Evidence of High-Level Processing in Binocular Rivalry

One of the most fascinating and challenging questions of cognitive neurosciences is what are the neural correlates of consciousness. We try to answer this question by studying patients having a dissociation between conscious perception and sensory stimulation. We studied patients with right brain damage (RBD) involving unilateral spatial neglect (USN). USN follows a lesion in the right frontoparietal cortex and involves lack of consciousness of visual stimuli (or parts of them) presented in the contralesional (left) side of space, without any sensory deficit [5]. Even if patients are unable to describe the left side of a stimulus, they show behavioural evidence of preserved visual analysis when tested implicitly [4]. To study visual consciousness in neglect patients, we used binocular rivalry. This involves showing different images to the two eyes. Instead of seeing both images simultaneously, neurologically normal people see one image for a few moments with no trace of the other, then they see the other image for a few moments with no trace of the first, then they see the first again, and so on for as long as they care to look. This phenomenon exhibits a dissociation between sensory input, which is unchanging, and consciousness, which changes continuously. There are two opposing explanations of binocular rivalry: low-level and high-level theories [8]. Blake [2] proposed that rivalry is resolved at a low level of the visual system, in the primary visual cortex, involving