Different neural processing of hole and no-hole stimuli in early stages of cortical and subcortical visual pathway

Abstract

Growing psychophysical evidence supported that the extraction of topological properties serves as the starting point of the formation of an object representation, especially with an initial step being to compute the absence and presence of a hole feature within an object. However, what constitutes the neural substrates of this early perceptual difference of hole and no-hole is still an unsolved question. Our previous study had demonstrated that there exists a privileged detection of stimuli with holes in the absence of awareness compared with no-hole stimuli, which suggested that the hole feature maybe processed via a subcortical pathway which bypassed the cortical site of visual pathway. Using functional magnetic resonance imaging fMRI, present study investigated the neural responses of the early stages of cortical (lateral geniculate nucleus (LGN) and early visual cortex) and subcortical pathway (superior colliculus (SC) and pulvinar), when visibility of the hole and no-hole stimulus is greatly reduced by backward masking. We found that, for no-hole stimuli, the neural activity of lateral geniculate nucleus and early visual cortex (cortical pathway) decreased as the stimuli was rendered more invisible. In contrast, for the hole stimuli, a increased response was observed in superior colliculus, pulvinar (subcortical pathway) and early visual cortex though it’s visibility was greatly attenuated by masking. The results indicate that a cortical route, via LGN and early visual cortex, is required to ‘drive’ a perceptual response of no-hole stimuli and in parallel, a subcortical pathway may possibly provide a route for processing the invisible hole stimuli. This distinct neural modulation of hole and no-hole stimuli may provide the possible neural mechanism for the perceptual difference between hole and no-hole stimuli that occurred early in the initial periods of the object representation.

Meeting abstract presented at VSS 2013