Rapid discrimination of visual patterns

Experiments involving the rapid discrimination of visual patterns are used to infer the spatial information available to an observer within the first few hundred ms of inspection. Eye movements are prevented by a very brief presentation of the stimulus, and the inspection interval is terminated by a presentation of a masking pattern. It is shown that detection of a single vertical target line segment, embedded in an array of differently oriented background segments, improves with the increase of mask delay. The reduction of the area in which the target may lie reduces the inspection time that is required to determine the target´s presence or absence. The phenomena are invariant under changes of the spatial scale within the fovea and parafovea. These results are interpreted in the context of a model in which the diameter of the area which can be searched in parallel is proportional to the distance in a feature space between the target and background elements. The geometry of this feature space is similar to the functional architecture of the visual cortex. A theory of texture perception based on a qualitative all-or-none feature space of textons is described. A quantitative model that is shown to be essentially equivalent to the previous theory in the limiting case of very large feature differences is proposed.