Posterior Parietal Cortex Neurons Encode

motion when the object is moving invisibly behind an occluder along an inferred trajectory (Assad and Hoppe-Seyler-Str 3 D-72076 Tü bingen Maunsell, 1995). Moreover, many neurons in area MST, usually referred to as visual tracking (VT) neurons (Sa-Germany kata et al., 1983), will discharge during steady-state SPEM, even in the absence of any retinal image slip, for example, if the pursued target disappears briefly Although this has not been tested The motion areas of posterior parietal cortex extract information on visual motion for perception as well as directly, it seems likely that these VT neurons may actually correspond to the ones responding to inferred object for the guidance of movement. It is usually assumed that neurons in posterior parietal cortex represent vi-motion while the eyes are stationary (Assad and Maunsell, 1995). The discharge during the disappear-sual motion relative to the retina. Current models describing action guided by moving objects work suc-ance of the target while the eyes are either stationary or moving could simply be a reverberation of retinal cessfully based on this assumption. However, here we show that the pursuit-related responses of a distinct image slip information that was collected and stored while the moving target was visible. However, this expla-group of neurons in area MST of monkeys are at odds with this view. Rather than signaling object image mo-nation is not able to account for the observation that the VT neurons will discharge if high-performance SPEM tion on the retina, they represent object motion in world-centered coordinates. This representation may are elicited by imaginary targets on the fovea, implied by cues confined to the visual field periphery outside simplify the coordination of object-directed action and ego motion-invariant visual perception. the receptive field (Ilg and Thier, 2003). Hence, a more appropriate view seems to be the assumption that these neurons respond to the percept of object motion, inde-Introduction pendent of whether or not object image slip is actually available on the retina. What is the coordinate system In order to exploit the advantages of foveal vision, we shift the image of an object of interest into the fovea by to which this neuronal representation in area MST references the object motion percept? Is it the retina? This making a saccadic eye movement, followed by smooth pursuit eye movements (SPEM) in the case of object might be suggested by the fact that this representation most probably builds on real object …