Conjunctions between motion and disparity are encoded with the same spatial resolution as disparity alone.

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Neurons in visual area MT are sensitive to transparent motion but lack subregions for opposing motion directions.
• Spatial resolution for disparity is known to be limited by receptive fields in primary visual cortex (V1).

Purpose of the Study:

• To investigate whether spatial resolution for combined motion and disparity is limited by MT or V1 receptive fields.
• To determine the neural basis of processing transparent motion and disparity conjunctions.

Main Methods:

• Developed a novel "joint motion/disparity grating" stimulus.
• Measured human observer spatial resolution for detecting motion/disparity conjunctions in transparent random-dot patterns with opposing motion directions across two depth planes.

Main Results:

• Human observers demonstrated spatial resolution for motion/disparity conjunctions similar to that for pure disparity gratings.
• Estimated limiting receptive field diameter to be 11 arcminutes, comparable to V1 and significantly smaller than MT receptive fields.
• Identified a slightly lower high-frequency cutoff (2.5 cycles per degree) for joint motion/disparity detection compared to disparity alone (3.3 cycles per degree) due to higher internal noise.

Conclusions:

• Information regarding motion/disparity conjunctions is present in V1 population activity.
• Perception of these conjunctions can be decoded from V1, even when such information is not explicitly represented in MT neurons.