How does orientation-tuned normalization spread across the visual field?

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Visuocortical responses rely on gain control, including surround suppression.
• Suppression strength varies with stimulus features like orientation similarity.
• The impact of orientation-tuned suppression on contrast responses is understudied.

Purpose of the Study:

• To investigate the role of orientation-tuned suppression in modulating contrast response functions (CRFs) in early visual cortex.
• To determine how feature similarity, specifically collinearity versus orthogonality, affects suppression strength.
• To examine the spatial spread of this tuned suppression across the visual field.

Main Methods:

• Used functional magnetic resonance imaging (fMRI) to measure brain activity in visual areas V1-V3.
• Presented observers with center-surround gratings where center and surround orientations were either collinear or orthogonal.
• Measured population contrast response functions (CRFs) across a range of center stimulus contrasts.

Main Results:

• Stronger suppression was observed when the surround grating was collinear with the center grating compared to orthogonal.
• This orientation-tuned suppression caused significant shifts in the population CRFs.
• The magnitude of the CRF shift was dependent on voxel spatial preference, primarily affecting voxels near the center-surround boundary.

Conclusions:

• Orientation similarity significantly influences the strength of surround suppression in early visual cortex.
• Tuned suppression primarily impacts neural populations with receptive fields at the center-surround boundary.
• These findings elucidate the feature-tuned gain control mechanisms shaping visual processing and perception.