The neural correlates of two forms of bistability: a comparison of binocular and monocular rivalry with fMRI

摘要

The neural correlates of binocular rivalry are of considerable interest as they may shed light on mechanisms of conscious awareness. In a related phenomenon, monocular rivalry, a composite image is shown to both eyes. The subject experiences perceptual alternations in which the two stimulus components alternate in salience. The experience is similar to perceptual alternations in binocular rivalry, although the reduction in visibility of the suppressed component is greater for binocular rivalry, especially at higher stimulus contrasts (O'Shea et al., 2009). We used fMRI at 3T to image activity in visual cortex while subjects perceived either monocular or binocular rivalry. The stimulus patterns were left/right oblique gratings with luminance contrasts of 9%, 18% or 36%. Remarkably, both binocular and monocular rivalry showed a U-shaped function of activation as a function of contrast, i.e. higher activity for most areas at 9% and 36%. The increased activation at higher contrast can be explained by neuronal response gain reflected in faster alternation rates, while that at low contrast can be explained by disinhibition (Wilson, 2007). The cortical activation for monocular rivalry included occipital pole (V1, V2, V3), ventral temporal, and superior parietal cortex. The additional areas for binocular rivalry included area V3A, lateral occipital areas (including MT+), and inferior parietal cortex, including temporoparietal junction (TPJ). The activation in V2 and V3 was reduced for binocular compared to monocular rivalry at the higher contrasts that evoked stronger binocular perceptual suppression, indicating that the effects of suppression are not limited to interocular suppression in V1.