Form and Motion Integration

Smith-Kettlewell Eye Research Institute, San Francisco CA

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Abstract

Sensitivity to motion is of vital adaptive significance. While single unit studies have provided detailed information on the dynamics of motion responses in individual cortical areas and human fMRI studies have mapped slow hemodynamic responses in multiple areas, neither approach provides an analysis of the functional dynamics of the entire motion processing network. We have developed EEG-based source-imaging and signal analysis tools that we will use to develop a predictive dynamical model of motion processing throughout cortex at a spatial resolution that is on the order of 2 cm or less. We propose to map the human cortical areas responsible for long-range apparent motion, using stimuli and analysis procedures that are analogous to those used to study direction selectivity in single-units. In Aim 1 we will use EEG-source imaging and perceptual measurements to compare the functional form of spatiotemporal interactions underlying long- versus short-range apparent motion and to map their sites of generation. The second experiment will vary the observer[unreadable]s task in order to determine the extent of top-down (feedback) influences on apparent motion processing. In a third experiment, a bistable apparent motion stimulus will be used to compare responses during episodes when apparent motion is perceived to when it is not. Beyond the general principle that development proceeds from primary sensory areas to association areas, very little is known about the development of extra-striate cortex in any species. Because long-range apparent motion activates cortical areas that are functionally distant from motion processing areas at the occipital pole, it is an ideal probe of development in these areas. The second Aim will apply recent technical developments in EEG source-imaging to the study of motion responses in the extra-striate cortex of typically developing humans infants between two and six months of age. We will test the hypothesis that long-range spatio-temporal interactions in the motion system is relatively precocious compared to spatial interactions in the form system. When strabismus or amblyopia are present during early development, the normal covariation between depth from disparity and monocular depth cues is broken when stereopsis is lost. We propose to test the developmental hypothesis that stereopsis serves an instructive role for the normal development of motion processing mechanisms sensitive to optic flow. This hypothesis is motivated by the finding that patients with strabismus have elevated thresholds for global motion in their normal acuity fellow eyes. A series of experiments will determine 1) whether timing abnormalities are associated with perceptual motion processing deficits 2) whether timing deficits are associated with deficient stereopsis and 3) whether the timing abnormalities are specific to stimuli that are undergoing apparent motion or whether they represent a more general disruption of temporal integration.