A selective impairment of motion perception following lesions of the middle temporal visual area (MT)

TLDR

The middle temporal visual area (MT) is known to be crucial for cortical analysis of visual motion. The study examined how chemical lesions of MT affect psychophysical thresholds in visual perception. Rhesus monkeys were trained on motion and contrast discrimination tasks using a dynamic random‑dot display and stationary gratings, and thresholds for direction discrimination and orientation discrimination were measured. Lesioning MT with ibotenic acid markedly increased motion thresholds while leaving contrast thresholds unchanged, indicating MT’s selective contribution to motion perception.

Abstract

Physiological experiments indicate that the middle temporal visual area (MT) of primates plays a prominent role in the cortical analysis of visual motion. We investigated the role of MT in visual perception by examining the effect of chemical lesions of MT on psychophysical thresholds. We trained rhesus monkeys on psychophysical tasks that enabled us to assess their sensitivity to motion and to contrast. For motion psychophysics, we employed a dynamic random dot display that permitted us to vary the intensity of a motion signal in the midst of masking motion noise. We measured the threshold intensity for which the monkey could successfully complete a direction discrimination. In the contrast task, we measured the threshold contrast for which the monkeys could successfully discriminate the orientation of stationary gratings. Injections of ibotenic acid into MT caused striking elevations in motion thresholds, but had little or no effect on contrast thresholds. The results indicate that neural activity in MT contributes selectively to the perception of motion.