The time to detect symmetries in square field patterns was measured. The same relationships among mean detection times for different symmetries was found in both well-practiced and naive subjects. When the task was to detect any symmetry, detection times were faster for multiply symmetry was faster than diagonal, singly symmetric ones. Horizontal-vertical symmetry was faster than diagonal, which was faster than centric. When the task was to detect specific symmetry, that is, vertical, horizontal,diagonal, or centric only, detection times were faster again for multiply symmetric patterns, suggesting that "irrelevant" symmetry facilitates performance. Errors and response times indicate that certain symmetries are more difficult to reject than others, depending on the type of symmetry to be detected. Thus, the results suggest interference effects arising from certain symmetries. The data are best accounted for by a model in which symmetry is encoded integrally. When decoding is required by the task, as in detection tasks, the observer performs a serial hierarchical decomposition of the code.U

A decline in performance on the Digit Symbol Substitution test related to aging is well documented. There is no agreement on the reason for the decline, however. In part, the lack of consensus with regard to changes on the test may be attributed to the limitations imposed by comparing groups on a single performance measure. In the present study, three forms of a Symbol‐Digit Substitution task that varied in difficulty level were administered to 125 persons between the ages of 30 and 92. On all forms there was a clear performance decline associated with age. The differences observed among the age group were interpreted as evidence for a change in a sensorimotor component and in two information‐processing operations: Symbol encoding and visual search.

It has been argued that principles of perceptual organization play an important role in the representation of a visual stimulus and that elderly adults may be deficient in perceptual unit formation. The present study examined the extent to which the Gestalt principles of grouping by proximity and similarity predicted the formation of large perceptual units that could affect performance in a visual search task. The verbal reaction time to determine the presence or absence of a target letter in arrays of 1, 5, or 9 elements was determined for young (20 years) and elderly (69 years) adults. Both age groups could take advantage of the organization implied by Gestalt principles in finding a target in the context of a small implied group. The elderly adults, however, were not able to organize a single perceptual unit composed of eight elements. Thus, although the visual search performance of the age groups was similar, the elderly adults did yield evidence of a perceptual organization deficit.

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