Aging differentially delays visual evoked potentials to checks and gratings

The effect of age on the latency of the major positive component (P1) of the transient visual evoked potential (VEP) was compared in 27 observers for check and sinusoidal grating patterns equated in fundamental spatial frequency; the tested spatial frequencies included 2.3, 4.6 and 6.9 c/deg. The ages ranged from 16 to 84 yr with all observers (except one, 20/25) having 20/20 or better acuity. Using linear regression analysis, we found a significant increase in latency with age for all spatial frequency-pattern combinations except 2.3 c/deg sinusoidal gratings. Moreover, while similar age-latency changes were obtained with 4.6 c/deg and 6.9 c/deg check and grating patterns, a significantly greater increase in latency with age was found with the 2.3 c/deg check than with the 2.3 c/deg grating pattern. We next examined the age-latency data with three additional mathematical models which included (a) a quadratic polynomial, (b) a log Y, and (c) separate regression lines for each of two age groups, 15-50 yr and 50-85 yr. The quadratic polynomial model was found to best describe the age-latency data. The polynomial functions were almost identical for gratings and checks at 4.6 and 6.9 c/deg. At 2.3 c/deg, however, as with linear regression analysis, the age-latency effect was stronger with checks than with gratings. These results suggest that age-dependent latency changes which were reported in the past using check stimulation may depend on different factors: in larger checks, either the higher harmonic spatial frequency components or an interaction between spatial frequency components contributes to the age-latency dependence. In smaller checks, however, the age effect is predominantly due to the fundamental spatial frequency.