Neuronal mechanisms for evaluating the visual scene across eye movements

As a foveate animal, the primate must redirect its gaze with saccadic eye movements to subject different objects to high resolution analysis. Though beneficial in extending the range of visual analysis, the saccade-and-fixate oculomotor strategy poses a problem to the visual system as it performs its analyses. Each saccade results in a whole-field displacement of the visual image across the retina. Nevertheless, we experience a stable visual percept, implying a brain mechanism for visuo-spatial correction. The experiments reported here examine the neural mechanisms underwriting this correction.In the first study, we sought to understand how the frontal eye field (FEF) gains access to information about ipsilateral space. Information about all of space, not just the contralateral hemifield, is a prerequisite for omnidirectional processes such as spatial remapping, a putative mechanism of visual stability. We found that one source of ipsilateral information is the superior colliculus (SC) on the opposite side of the brain. In the second study, we set out to test a major prediction of one theory of visual stability. This theory invokes the function of neurons with shifting receptive fields (RFs) as a mechanism for achieving transaccadic visual stability. Shifting RFs effectively sample the same region of space twice, presaccadically and postsaccadically, and a percept of stability may rely on how well the samples match. This theory has the salient prediction that neurons in areas where shifting RFs are found should be sensitive to changes that occur to stimuli during saccades. We tested this prediction by recording from FEF neurons while monkeys performed a task during which a probe changed along a particular dimension during a saccade. We found that FEF neurons are indeed sensitive to intrasaccadic alterations of visual stimuli. In a third and final study, we sought to bridge the neuron-behavior gap by recording from FEF neurons while monkeys performed a visual stability judgment task that probed their capacity to detect changes occurring during saccades. We found that monkeys are clearly able to discern whether a stimulus is stable or unstable during a saccade and moreover that FEF neural activity is predictive of monkey psychophysical performance