Abstract Binocular rivalry refers to the alternating perception of dissimilar images presented simultaneously, one to each eye. Until recently it was thought that binocular rivalry was resolved early in the visual pathway. However, recent data have challenged this notion, by demonstrating that activity in higher visual regions correlates with perception during rivalry. The present thesis proposes a novel model for the neural mechanism of binocular rivalry that is consistent with this data.
The interhemispheric switch model proposes that during rivalry one hemisphere selects one image, the other hemisphere selects the rival image, and the perceptual alternations correspond to hemispheric alternations (interhemispheric switching). This higher-level model can also accommodate attentional factors that have been shown to be relevant during rivalry in both recent and early work. Experimental data in support of the interhemispheric
switch model is provided by unilateral hemisphere activation and disruption techniques during binocular rivalry (caloric vestibular stimulation and transcranial magnetic stimulation, respectively). These experiments demonstrate that activating or disrupting a single hemisphere's temporo-parietal region significantly alters the time spent perceiving one image relative to the other. This finding cannot be explained by within-hemisphere competition models, but is predicted by the interhemispheric switch model.
The present thesis also reports the finding that the rate of binocular rivalry is significantly slower in subjects with bipolar disorder (manic depression) than in normal control subjects, in subjects with major depression and in subjects with schizophrenia. A preliminary report is also made on rates of rivalry in first-degree well relatives of bipolar probands and in monozygotic twin pairs. The finding of slow binocular rivalry in bipolar disorder,
together with the interhemispheric switch model of rivalry and a large body of evidence on hemispheric asymmetries of mood and mood disorders, suggests a new model for the pathophysiology of bipolar disorder, the 'sticky switch' hypothesis.
The thesis concludes by discussing the role of binocular rivalry research in the scientific study of consciousness. It is suggested that while binocular rivalry provides an excellent approach to the identification of neural correlates of visual consciousness, it is the neuronal constitution of visual consciousness that science seeks to understand. Because there are no clear strategies to distinguishing correlates from the actual constituents of consciousness, it is concluded that the problem posed by the correlation/constitution distinction represents the major empirical obstacle facing the scientific study of consciousness.