Normal aging and the perception of curvature shapes.

PURPOSE The present study assessed whether different curve geometries involve different perceptual processing levels and whether these perceptual requirements can interact with the normal aging process. METHODS Amplitude thresholds for three different curve types were assessed for young and older observers using 2AFC psychophysical methods. The stimuli were individually adjusted for visibility. The three stimulus types evaluated represented a bell shape, a quadratic, and a compressed arc function. RESULTS As predicted, the geometry influenced the perception of curvature where the compressed arc was most difficult to perceive followed by the quadratic and bell-shaped curves. Moreover, older observers showed relatively higher thresholds for the quadratic and compressed arc shapes, while they had similar thresholds to the younger observers for the bell-shaped function. CONCLUSIONS In general, the data support the notion that aging affects the processing of curvature requiring the integration of oriented receptors. This is in accordance with studies that have found reduced orientation selectivity of cortical neurons in senescent animals. Our findings suggest that older observers would have more difficulties with form discrimination tasks where curvature is an inherent component of the image and also predict age-related differences in perceiving ophthalmic lens-induced distortions.