Modeling the contrast-sensitivity functions of older adults.

To determine whether a parabolic template is a good description of the contrast-sensitivity functions (CSF's) exhibited by older adults, the curve-fitting method of Pelli et al. [J. Opt. Soc. Am. A 3(13), P56 (1986)] was applied to contrast-sensitivity data from 100 older subjects (ages 53-85 years). Although the method resulted in reasonable fits for most subjects, closer inspection revealed that this technique may be problematic. A significant number of observers had functions that were nonparabolic, and for many subjects the error tended to be concentrated at the peak of the CSF. In addition, in contrast to the study of Pelli et al., the peak contrast sensitivities of the subjects were only weakly related to Pelli-Robson contrast sensitivity and letter acuity. The data were also fitted with an asymmetric function of variable shape. Whereas this function provided a better fit to the nonparabolic CSF's, it resulted in inferior fits to most of the remaining data. These results demonstrate that the spatial CSF's of older adults cannot be described by a single parametric curve such as a parabola or a function of an exponential and that Pelli-Robson contrast sensitivity and letter acuity are not adequate predictors of their peak contrast sensitivities.