Shape perception is altered by normal aging

PURPOSE: To compare the effects of aging on two shape-discrimination tasks: a closed shape task (radial frequency [RF] patterns) and a Glass pattern coherence task (discrimination of global shape signal from textured noise). We hypothesized that aging would impair the extraction of shape from texture more than the discrimination of closed shapes, consistent with evidence that aging impairs the ability to suppress irrelevant information when segmenting contours from noise.

METHODS: Fourteen younger (19-38 years) and 14 older (62-72 years) adults participated. Contrast-detection thresholds were measured for the RF and Glass stimuli, and then shape-discrimination tasks were performed using stimuli of 5-fold each individual's contrast threshold. The threshold sinusoidal amplitude for the discrimination of an RF3 (triangular) versus an RF4 (square) was measured, in addition to the threshold signal coherence level for the discrimination of concentric from radial Glass patterns.

RESULTS: Older adults had elevated shape-discrimination thresholds: RF: mean older = 27 second arc, younger = 18 second arc, t(26) = -3.14, P < 0.01; Glass patterns mean coherence: older = 29%, younger = 16%, t(26) = -5.67, P < 0.01. Relative to younger adult performance, the Z-scores for older adult performance on the Glass task were higher than the RF task (paired t-test; P < 0.05).

CONCLUSIONS: Shape perception is not robust to the effects of aging. Greater deficits were manifest for the discrimination of shape from texture than for the discrimination of closed contours.