Contrast dependency of motion-onset and pattern-reversal VEPs: interaction of stimulus type, recording site and response component.
We compared the contrast dependency (from 0.4 to 98%) of the visual evoked potential (VEP) to motion onset and to pattern reversal at an occipital and lateral recording site using sinewave grating stimuli of 0.9 c/deg, drifting at 4.9 deg/sec. Two differing VEP components were identified: a positive component, peaking at around 130 msec, dominating the occipital derivation, enhanced in pattern-reversal stimulation, a high-threshold, late-saturating contrast response characteristic with a half-amplitude contrast above 7%; and a negative component at around 180 msec, dominating the lateral derivation, enhanced in motion-onset stimulation, exhibiting a low-threshold, saturating contrast characteristic with a half-amplitude contrast below 4%. The results suggest: (1) The negative component (N180) represents motion mechanisms, located more laterally, while the positive component (P100-P130) represents form-processing mechanisms, located near the V1/V2 areas. (2) A pattern-reversal stimulus triggers both form-processing and motion mechanisms that can be discriminated by latency. In an occipital derivation, the clinical reversal VEP P100 will be little contaminated by motion responses.
Bach
M
M
Universitäts-Augenklinik, Killianstr, Freiburg, Germany. bach@uni-freiburg.de
Ullrich
D
D
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors