Larger effect of aging on the perception of higher-order stimuli.

Widespread deficits are known to accompany normal aging. Contrast thresholds of older and younger observers were measured for static and drifting gratings defined by luminance (first-order) or by contrast (second-order), and for a temporally segmented second-order motion stimulus. Results showed that older individuals had a larger threshold elevation for the perception of second-order stimuli than for the perception of first-order stimuli. This suggests a dissociation between the mechanisms underlying the perception of first and second-order stimuli, and demonstrates that aging may affect the more numerous processing steps required for the analysis of higher level stimuli.