Horizontal-vertical structure in the visual comparison of rigidly transformed patterns.

Visual recognition of patterns reflected or rotated through 180 degrees (point-inverted) depends critically on their positional symmetry and separation in the field. A possible explanatory scheme suggested a description of internal pattern representation structures and simple internal operations that naturally involved a horizontal-vertical reference system. Predictions of the scheme were tested here in three experiments. Subjects made same-different judgments on pairs of random-dot patterns briefly presented in various arrangements and related by reflection, point-inversion, or identity transformation, or paired at random. Experiment 1 tested reflected patterns and verified the importance of orientation of the reflection axis relative to display-configuration axis. Experiment 2 demonstrated an oblique effect of configuration on performance with reflected patterns, but not with identical or point-inverted patterns. Experiment 3 demonstrated a vertical shift effect of configuration on performance with point-inverted patterns, but not with identical or reflected patterns. We concluded that in same-different pattern comparisons, a horizontal-vertical reference system appears fundamental in determining the nature of and operations upon internal pattern representations.