Neuropsychological Evidence of High-Level Processing in Binocular Rivalry

One of the most fascinating and challenging ques-tions of cognitive neurosciences is what are the neuralcorrelatesofconsciousness. Wetrytoanswerthisques-tionbystudyingpatientshavingadissociationbetweenconsciousperceptionand sensory stimulation.We studied patients with right brain damage (RBD)involving unilateral spatial neglect (USN). USN fol-lows a lesion in the right frontoparietal cortex and in-volveslack of consciousnessof visual stimuli (or partsof them) presented in the contralesional (left) side ofspace, without any sensory deficit [5]. Even if patientsare unable to describe the left side of a stimulus, theyshowbehaviouralevidenceofpreservedvisualanalysiswhen tested implicitly [4].Tostudyvisualconsciousnessinneglectpatients,weusedbinocularrivalry. Thisinvolvesshowingdifferentimages to the two eyes. Instead of seeing both imagessimultaneously, neurologically normal people see oneimage for a few moments with no trace of the other,then they see the other image for a few moments withnotraceofthefirst, thentheysee thefirst again,andsoon for as long as they care to look. This phenomenonexhibitsa dissociationbetweensensoryinput,whichisunchanging,andconsciousness,whichchangescontin-uously.Therearetwoopposingexplanationsofbinocularri-valry: low-level and high-level theories [8]. Blake [2]proposed that rivalry is resolved at a low level of thevisual system, in the primary visual cortex, involving