Spatial frequency and the pattern onset-offset response.
Visually evoked responses (VERs) were recorded with vertical sinusoidal gratings presented in the on-off mode at rates of 0.5 and 1 Hz. Stimulus spatial frequency ranged from 0.5 to 16 c/deg and its contrast varied from near-threshold to the value of 0.3. At low spatial frequencies, 0.5 and 1 c/deg, the onset and offset VERs were of similar shape, magnitude and contrast dependence. At spatial frequencies higher than 2 c/deg the onset VERs were usually larger and persisted at lower contrast levels than the offset VERs. The results are consistent with the hypothesis that a gradual transition from the operation of transient channels to the operation of sustained channels takes place on increasing stimulus spatial frequency and that within a wide spatial frequency range (at least from 2 to 8 c/deg) suprathreshold gratings effectively stimulate both types of channels. It is confirmed that both onset and offset VERs are delayed at high spatial frequencies. In addition, a longer delay of the late onset waves was found in comparison with the delay of the early onset waves.
D000293:Adolescent; D000328:Adult; D005074:Evoked Potentials, Visual; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D014792:Visual Acuity