Pooled, but not single-neuron, responses in macaque V4 represent a solution to the stereo correspondence problem

Area of Science:

• Neuroscience
• Computational Neuroscience
• Vision Science

Background:

• Binocular disparity is crucial for depth perception, requiring neurons to match visual features between eyes.
• The visual pathway from V1 to IT cortex addresses the correspondence problem, with V4 proposed as a key stage.
• The precise role of V4 versus V1 in correspondence remains debated, with evidence suggesting early processing in V1.

Purpose of the Study:

• To investigate whether macaque V4 neurons contribute to solving the correspondence problem for depth perception.
• To compare disparity representation in V4 with that in V1.
• To determine if pooled V4 neuronal responses, rather than individual neurons, reflect correspondence solutions.

Main Methods:

• Recorded single-unit V4 neuronal responses to random-dot stereograms with varying degrees of anticorrelation.
• Manipulated anticorrelation by reversing dot contrast proportionally.
• Analyzed individual neuron tuning curves and population-pooled responses.

Main Results:

• Individual V4 neuron tuning amplitudes decreased rapidly to a baseline with increasing anticorrelation.
• The shape of individual V4 tuning curves changed gradually.
• Population-pooled V4 responses showed a gradual decrease in amplitude towards zero with increasing anticorrelation.
• V4 population activity provides disparity information consistent with correspondence solutions.

Conclusions:

• Pooled V4 neuronal responses, not individual neurons, represent a solution to the correspondence problem.
• Disparity representation in V4 is more advanced than in V1.
• Population readout of V4 activity effectively decodes depth information.