Segregation of object and background motion in visual area MT: Effects of microstimulation on eye movements

To track a moving object, its motion must first be distinguished from that of the background. The center-surround properties of neurons in the middle temporal visual area (MT) may be important for signaling the relative motio n between object and background. To test this, we microstimulated within MT and measured the effects on monkeys' eye movements to moving targets. We f ound that stimulation at "local motion" sites, where receptive fields posse ssed antagonistic surrounds, shifted pursuit in the preferred direction of the neurons, whereas stimulation at "wide-field motion" sites shifted pursu it in the opposite, or null, direction. We propose that activating wide-fie ld sites simulated background motion, thus inducing a target motion signal in the opposite direction. Our results support the hypothesis that neuronal center-surround mechanisms contribute to the behavioral segregation of obj ects from the background.