Age-related decline of contrast sensitivity for second-order stimuli: earlier onset, but slower progression, than for first-order stimuli.

Many visual functions are known to decline during aging (P. D. Spear, 1993). However there has been no clear description as to how contrast sensitivity for second-order stimuli changes across the adult life span. Based on different mechanisms underlying perception of first-/second-order stimuli (Z. L. Lu & G. Sperling, 2001), and J. Faubert's (2002) theory of visual perception and aging, it is expected that perception of these two types of stimuli will change in different ways during aging. In this study we have measured contrast sensitivity for both first- and second-order stimuli in 141 subjects aged from 19 to 79 years old. The results have shown no gender effect but an evident aging effect, i.e., a progressive decline during aging, for perception of both types of stimuli. We have also proposed a piecewise linear model to interpret our data. Based on this model, contrast sensitivity for second-order stimuli begins to decline significantly earlier than for first-order stimuli, but with a slower rate of progression. We suggest the earlier decline for perception of second-order stimuli may be interpreted as reflecting a greater complexity of second-order processing.