Human visual system modulation transfer function measured by evoked potentials

Visual potentials evoked by checkerboard pattern reversal were studied using temporal frequencies between 3 and 12 Hz (i.e. 6 and 24 reversal per sec, with sinusoidal or square wave modulation). Sinusoidal modulation evoked lower amplitude potentials than square wave modulation, at all frequencies used. Evoked potential amplitude vs temporal stimulation frequency curves for both modulations showed a maximum at approximately 4 Hz, with a slight decrease for lower frequencies, and a steep fall-off for higher frequencies starting at 7 Hz (values beyond 12 Hz were not measurable), unlike de Lange's psychophysical data. Accordingly, different brain generators are hypothesized for evoked potentials and psychophysical functions.