Interitem structure and the facilitation of simultaneous comparison.

The effects of bilateral display symmetry on simultaneous comparison were examined. Experiment 1 demonstrated that symmetric letter pairs are classified as same more rapidly and accurately than asymmetric letter pairs. Experiments 2 and 3 disentangled the contributions of single-letter and whole-display symmetries (these being confounded in normal letter pairs) and showed that the primary determinant of response facilitation is the presence and registration of interitem relational structure. The last three experiments suggested that this facilitation does not arise from the detection and diagnostic utilization of symmetry. It is concluded that bilateral display symmetry facilitates the normal operations of form comparison. The early operations of field segmentation are discussed as the probable locus for this facilitation effect.