We have recorded patterns electroretinograms (PERGs) and visual evoked potentials
(VEPs) from 14 elderly subjects (mean age 72 yr) and 12 young subjects (mean age 21
yr) in response to stimulation by high contrast sinusoidal grating patterns of variable
spatial frequency (at 9 Hz) and temporal frequency (at 1.7 c/deg). The major effect
of aging on the PERG was an aspecific reduction in amplitude (of about 40%) at most
spatial and temporal frequencies, together with a small but systematic phase lag.
Control measurements suggest that senile miosis may be responsible for the phase lag,
but not for the reduction in amplitude. The effects of aging on the VEP were more
dramatic and depended on the spatial and temporal properties of the stimulus. VEP
amplitudes (at 1.7 c/deg) were significantly lower for the aged at low temporal frequencies
(below about 6 Hz), but were similar at high temporal frequencies. At 9 Hz, there
was no effect of spatial frequency on VEP amplitude. At high temporal frequencies
(above 10 Hz), the latencies of VEPs (estimated from the rate at which phase varied
with temporal frequency) were similar for old and young (94 and 99 msec respectively).
Below 10 Hz, however, the latencies of the old observers was much greater (153 compared
with 108 msec). The second-harmonic phase of VEPs of the old but not the young decreased
considerably with spatial frequency, by about 1.9 pi radians (52 msec) over the range
from 0.5 to 11 c/deg. The selective reduction in amplitude at low temporal frequencies,
the longer latencies at low temporal frequencies and the phase lag at high spatial
frequencies are consistent with the hypothesis that mechanisms sensitive to high spatial
and low temporal frequencies are selectively degraded by aging.