Computation of Locally Parallel Structure
A Moire-like effect can be observed in dot patterns consisting of two superimposed copies of a random dot pattern where one copy has been expanded, translated, or rotated. One perceives in these patterns a structure that is locally parallel. Our ability to perceive this structure is shown by experiment to be limited by the local geometry of the pattern, independent of the overall structure or the dot density. A simple representation of locally parallel structure is proposed, and it is found to be computable by a non-iterative, parallel algorithm. An implementation of this algorithm is demonstrated. Its performance parallels that observed experimentally, providing a potential explanation for human performance. Advantages are discussed for the early description of locally parallel structure in the course of visual processing.