Disparity- and size-selective neurons in macaque area V4 as a neural basis for size constancy.
Shingo Tanaka, Ichiro Fujita
The perceived size of an object remains relatively stable despite changes in the size of retinal images accompanying changes in distance from the observer. In this perceptual phenomenon (size constancy), the brain uses distance information for calibrating the perceived size. Binocular disparity provides a clue about distance. To examine interaction between disparity and stimulus size information, we recorded neuronal responses in macaque V4, a visual cortex known to be involved in stereopsis and size discrimination. Random dot stereograms (RDSs) were used for visual stimuli. A majority of neurons were selective for both binocular disparity and cyclopean image size. In some cells, the tunings for binocular disparity and size showed significant interaction;the preferred size shifted to larger for an RDS presented nearer. This behavior of V4 cells was consistent with psychophysical performance of human observers tested with the same stimuli. The results suggest that V4 cells contribute to size constancy.