Two Disparity Channels in Human Visual Cortex With Different Contrast and Blur Sensitivity

Area of Science:

• Neuroscience
• Vision Science
• Computational Neuroscience

Background:

• Human depth perception relies on processing horizontal disparities.
• Understanding the neural basis of disparity processing is crucial for vision science.

Purpose of the Study:

• To characterize contrast and blur sensitivity of horizontal disparity subsystems.
• To link these sensitivities to monocular input properties.

Main Methods:

• Recorded steady-state visual evoked potential (SSVEP) amplitudes using dynamic random dot stereograms (DRDSs).
• Varied disparity magnitudes, half-image contrasts (2.5%-80%), and Gaussian blurs (1.4-12 arcmin).
• Measured monocular contrast and blur sensitivity separately.

Main Results:

• Disparity responses showed maximal first and second harmonics for disparity gratings and disparity planes, respectively.
• The first harmonic was more sensitive to contrast and blur than the second.
• The second harmonic exhibited higher contrast sensitivity.

Conclusions:

• The first harmonic reflects neurons sensitive to relative disparity and higher spatial frequencies.
• The second harmonic likely represents neurons sensitive to absolute disparity and lower spatial frequencies.
• SSVEPs offer objective measures of disparity processing, distinguishing relative and absolute disparity mechanisms.