Human cortical responses to variations of the interocular correlation of binocular signals

The human visual system has an impressive ability to extract tiny differences from the left and right retinal images to produce the perception of depth. Moreover, the perception of depth is robust to a considerable amount of noise between the two images. Both these features of human vision contribute to the effectiveness of 3D imaging systems. Recent study of brain mechanisms for stereo has identified that there are multiple sites within the brain that respond to stereo depth, potentially implying that an effective 3D imaging system must deliver effective stimulation to multiple and differentiated brain systems. Here, we measure the neural responses of the visual cortex when tested a disparity-defined stimulus whose degree of interocular correlation was varied systematically. Neural responses were measured with functional magnetic resonance imaging (fMRI). This approach allowed us to obtain simultaneously measurements of the pattern of behavioral and neural responses to degraded binocular stimulation. Behavioral performance for the correct identification of binocular depth improved as expected with increasing degrees of binocular correlation. By comparison, the Blood Oxygen Level Dependent (BOLD) signal showed no consistent relationship with different levels of interocular correlation, although several of the visual cortical areas were strongly activated by the binocular stimuli. Preliminary analysis suggests that investigations of binocular vision that use fMRI need to adopt a multivariate approach to determine differences in neural responses to disparity-defined stimuli.