Visual comparison of rotated and reflected random-dot patterns as a function of their positional symmetry and separation in the field

Subjects viewed pairs of random-dot patterns which were presented in a number of arrangements varying in the transformations applied to the patterns, in the distance between the patterns, and in the symmetry of the pattern positions with respect to the point of fixation. The task was to judge whether the patterns were “the same” taking into account possible rotations or reflections, or “different”. It was found that correct judgements for identical patterns were most affected by the distance between the two patterns, whereas correct judgements for patterns where one had been rotated through 180° or reflected were most affected by the symmetry of the pattern positions. A scheme modelling the visual recognition of transformed patterns, sufficient to explain the results, is presented.