Contrast Normalization Accounts for Binocular Interactions in Human Striate and Extra-striate Visual Cortex.

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Binocular viewing involves complex interactions between visual inputs from both eyes within the visual cortex.
• Understanding these interactions is crucial for comprehending visual processing and perception.

Purpose of the Study:

• To investigate binocular interactions in the human visual cortex using steady-state visual evoked potentials.
• To characterize two forms of binocular interaction: interocular suppression and inter-eye input modulation.
• To determine if these interactions share common underlying mechanisms and how they vary across visual areas.

Main Methods:

• Utilized source-imaged steady-state visual evoked potentials (ssVEPs) with dichoptic stimuli.
• Analyzed responses to stimuli presented to each eye separately (self-terms) and interactions between eyes (intermodulation [IM] terms).
• Applied divisive gain control models to quantify interaction patterns across visual areas (V1, V3a, hV4, hMT+, lateral occipital cortex).

Main Results:

• Identified interocular suppression, where responses to one eye's stimulus are reduced by the other eye's stimulus, varying by visual area (strongest in V1/V3a, weakest in lateral occipital cortex).
• Observed intermodulation (IM) responses, indicating direct interaction between eyes, strongest in V1 and weakest in hV4.
• Found that both suppression and IM responses share a common gain control nonlinearity across cortical areas.

Conclusions:

• Both interocular suppression and direct inter-eye interactions in the visual cortex share a common gain control mechanism.
• Distinct patterns of excitatory and suppressive contributions characterize binocular interactions along the visual cortical hierarchy.
• These findings provide insights into the neural basis of binocular vision and visual information integration.