Neural Visual Coding: Image to Object Representation

Johns Hopkins University, Baltimore MD

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Abstract

DESCRIPTION (provided by applicant): Research is proposed to advance our understanding of the neural mechanisms of visual perceptual organization and their relation to selective attention. The long-term objective is to understand the interface between sensory representations and cognitive processes at the neural signal level. The proposed research focuses on the mechanisms of figure-ground organization as evident from the neural representation of border ownership, i.e., the assignment of contours to objects. The general method is single-cell recording from the visual cortex of awake behaving macaques. Three broad aims have been identified for the next five years. The first aim is to provide quantitative descriptions of the spatial integration mechanisms of border ownership selective V2 neurons. Previous studies have shown that these mechanisms extend far beyond the classical receptive field of the neurons. Two methods with factorial design will be applied. These methods allow to measure nonlinear interactions of the extra-classical regions with the classical receptive field as well as interactions between extra-classical regions. The two methods are complementary. One uses fragmentation of figures, the other uses occlusion of critical features. The second aim is to study persistence of figure-ground organization in the visual cortex. Experiments are proposed to (1) determine the influence of the type of figure-ground cue and its duration on the subsequent persistence of border ownership signals, (2) determine whether the persistence depends on attention being directed to the figure, and (3) whether border ownership signals persist across eye movements and stimulus movements. The third aim is to study the role of the neural organization mechanisms in object-based selective attention. Building on previous results showing that V2 neurons combine border ownership coding with the influence of volitional selective attention, new experiments will test visual conditions in which an object is partially occluded, so that only two unconnected portions of it remain visible. The results will show whether the border ownership mechanisms can link features across the gap, and whether object-based attention can do so. The proposed research will help to clarify the basis of selective attention which is important for understanding both normal and impaired vision. Although the proposal is focused on vision, the research will help to identify the sensory-cognitive interface also in other modalities. The insight gained from this project will contribute to the understanding of the basis of cognitive disorders such as dyslexia. PUBLIC HEALTH RELEVANCE Selective attention is perhaps the most important function in vision. We can choose to process the words in one line of text and ignore all others, which enables us to read. But sometimes we do not see things that are right in front of our eyes-the cause of many traffic accidents. Dyslexic children cannot detect the difference between strings of letters that others can easily see. The goal of the proposed research is to understand a process in the brain that dissects images into objects before objects are recognized, providing an internal representation from which attention can select.