Form vision in the periphery
Prof. Bosco Tjan
To perceive form, small local features detected in the early stages of visual processing must be selectively integrated to form larger coherent shapes. The precise nature of this selective integration process, which appropriately separates and integrates local features, is largely unknown. A form-vision deficit in the peripheral visual fields, known as crowding, provides a useful model for studying this selective integration process. In peripheral vision, flanking an otherwise identifiable target can impair identification of the target. In a series of psychophysical and fMRI experiments, we concluded that crowding cannot be explained by the spatial-tuning properties of the periphery or the spatial uncertainty for isolated features. Instead, crowding seems to be caused by an inability to segment or select features that are within a range equal to the average receptive-field size of an V2 neuron at the given eccentricity.