Violations of Symmetry and Repetition in Visual Patterns

Observers were asked to detect small violations in otherwise left-right symmetric or repeated line patterns. The decision time for symmetric patterns tended to be shorter than for repeated patterns, confirming an intuitive impression that symmetry is a very easily extracted feature, even of otherwise random patterns. The importance of the pattern midline in determining the salience of symmetry was investigated by systematically controlling the position of the violations in the patterns. Small departures from symmetry near the midline were much easier to detect than the same violations in a repeated pattern, but there were no differences where the violation was at the edge of the pattern. The salience of symmetry seems to a considerable extent to depend upon the ease of comparing spatially-contiguous elements near the midline of the pattern. However, both symmetry and departures from it are easier to detect than repetition, even when the nature of the violation is random.