Spatial integration of motion signals in Macaque MT

The processing of moving stimuli presents many challenges to the visual system. Among the problems that must be solved are (1) that much of the motion information in early visual areas is ambiguous due to the aperture problem and (2) that suppressive surround mechanisms become counterproductive when the visual stimulus is weak. Neurons in the motion processing middle temporal visual area (MT) are able to overcome both of these problems through the spatial integration of motion signals. We have studied the integration of visual motion in alert macaque monkeys using extracellular electrodes to record from MT. Specifically, we have examined how the response properties of motion integration in MT generalize across different visual stimuli. We demonstrate that MT neurons systematically integrate the motion of diverse stimuli such as dots, gratings, plaids, bars and barber poles in accordance with the expectations of motion integration models. We also show that MT neurons improve spatial integration by decreasing the strength their suppressive surrounds for low contrast stimuli but not for other forms of noisy stimuli.