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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 motion between object and background. To test this, we microstimulated within MT and measured the effects on monkeys' eye movements to moving targets. We found that stimulation at "local motion" sites, where receptive fields possessed antagonistic surrounds, shifted pursuit in the preferred direction of the neurons, whereas stimulation at "wide-field motion" sites shifted pursuit in the opposite, or null, direction. We propose that activating wide-field 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 objects from the background.

Summary The goal of the current study was to investigate the frame of reference at an early point in the ascending We examined the frame of reference of auditory reauditory pathway, namely the inferior colliculus (IC). The sponses in the inferior colliculus in monkeys fixating IC is situated above the convergence of binaural signals visual stimuli at different locations. Eye position moduin the superior olivary complex (for review, see Ehret, lated the level of auditory responses in 33% of the 1997), and nearly all input to all higher areas passes neurons we encountered, but it did not appear to shift through it. Lesions of the IC can cause deficits in sound their spatial tuning. The effect of eye position on audilocalization behavior (Wagner, 1993; Kelly and Kavatory responses was substantial—comparable in magnagh, 1994; Zrull and Coleman, 1997). Neurons sensitive nitude to that of sound location. The eye position signal to the locations of sounds in space have been reported appeared to interact with the auditory responses in at by a variety of studies using free field acoustic stimuli least a partly multiplicative fashion. We conclude that