Internal representations and operations in the visual comparison of transformed patterns: effects of pattern point-inversion, position symmetry, and separation.

A scheme for visual pattern recognition is described. It is supposed, amongst other things, that patterns are internally represented by the visual system in terms of local features, spatial-order relations between local features, and global spatial relations specifying approximate pattern position with respect to the point of fixation. It is further supposed that there are two distinct types of internal operation that may be applied to the components of internal representations in the process of pattern comparison: typically a discrete spatial-order-reversal operation and a continuous position-shift operation. Some general predictions of the scheme are tested against data obtained in an experiment using random-dot patterns that were subjected to rigid transformations and presented at various locations along the horizontal meridian. Patterns were presented sequentially, in pairs, to subjects in a "same-different" comparison task. Pattern pairs were to be responded to as "same" if they were identical or related by point-inversion (planar rotation through 180 degrees) or responded to as "different". Extending earlier findings, the present results showed that "same"-detection performance for identical and point-inverted patterns depended differentially on the distance between the patterns and the symmetry of the pattern positions about the point of fixation in a manner consistent with the predictions of the scheme.