Mechanisms of motion vision in the human have been
studied extensively by psychophysical methods but less
frequently by electrophysiological techniques. It is the
purpose of the present investigation to study electrical
potentials of the eye (electroretinogram, ERG) and of the
brain (visual evoked potential, VEP) in response to moving
regular square-wave stripe patterns spanning a wide range
of contrasts, spatial frequencies, and speeds. The results
show that ERG amplitudes increase linearly with contrast
while VEPs, in agreement with the literature, show an amplitude
saturation at low contrast. Furthermore, retinal responses
oscillate with the fundamental temporal stimulus frequency
of the moving pattern while brain responses do not. In
both the retina and the brain, the response amplitudes
are tuned to certain speeds which is in agreement with
the nonlinear correlation-type motion detector. Along the
ascending slopes (which means increasing amplitudes) of
the tuning functions, the ERG curves overlap at all spatial
frequencies if plotted as a function of temporal stimulation
frequency. The ascending slopes of the tuning functions
of the VEP overlap if plotted as a function of speed. The
descending slopes (which means decreasing amplitudes) of
the tuning functions show little (ERG) or no (VEP) overlap
and the waveforms at high speeds approach pattern-offset-onset
responses. These observations suggest that in the retina
motion processing along the ascending slopes of the tuning
curves takes place by coding the temporal stimulation frequency
which depends on the spatial frequency of the moving pattern.
In the brain, however, motion processing is by speed independent
of spatial frequency. Simple calculations show that the
VEP information is decoded from the ERG signal into a speed
signal.
Abnormalities of coherent motion processing in strabismic amblyopia: Visual-evoked potential measurements
