A great deal of clinical, behavioral, and physiological evidence supports the notion that the posterior parietal cortex in primates plays an important role in localizing visual stimuli in the environment, in analyzing visual motion, and in guiding movements. The proposed experiments will examine whether one area in posterior parietal cortex, the lateral intraparietal area (LIP), encodes a predictive representation of the motion of objects of interest. Prediction is essential for visual perception, supporting constancy of object representation when visual information is incomplete, such as when a moving objects becomes occluded. The question of whether LIP neurons provide a predictive representation of the movement of visual stimuli will be investigated in macaque monkeys trained in behavioral tasks. As a first test, neuronal signals will be identified that do not depend on the presence of a visual stimulus, for example, signals that persist when a moving stimulus passes behind an occluder. Neuronal activity will also be compared under conditions in which the expected motion of a visual stimulus is at odds with movements that the animal might make to guide or acquire the stimulus. Neuronal activity that cannot be directly related to sensory input or the animal's plan to move may encode a predictive representation of stimulus motion. Second, if LIP neurons predict motion, it would be expected that their activity should be related to the animal's subjective perception of motion. In the case of a moving stimulus that becomes occluded, the subjective perception of motion can be strengthened or weakened by changing the apparent depth of the occluder relative to the plane of motion, using stereoscopic cues. If LIP activity signals the expectation of motion, it should be stronger when the relative depths of the occluder and stimulus are consistent with stimulus motion. In addition, if LIP cells are presented with an apparent motion stimulus in which the perceived direction of motion is bistable, the cells' activity should covary with the animal's perceptual report of stimulus direction. Evidence of this sort would suggest that LIP is more concerned with the predicted motion of the stimulus than with the actual motion stimulus to the retina.
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