Origins and Implications of Frequency-Doubling in the Visual Evoked Potential

摘要

The origins and implications of frequency-doubling in the visual evoked potential (VEP) were investigated. Previous research demonstrated that frequency-doubling occurs in humans when sinusoidal but not square wave luminance modulation is used to elicit the VEP, but little else is known about this intriguing phenomenon. Six adult humans viewed luminance and chromatic gratings that were presented using three different spatiotemporal combinations: 4 c/deg-3Hz, 4 c/deg-6 Hz, and 12 c/deg-3Hz. VEP's were recorded monopolarly from Oz using an ear reference and were subjected to a Fourier analysis. The results showed that frequency-doubling occurred only using sinusoidal luminance contrasts at 4 c/deg-3 Hz, although the relative strength of higher harmonic responses was greater for both sine- and square-wave luminance contrasts at 4 c/deg-3 Hz, although the relative strength of higher harmonic responses was greater for both sine- and square-wave luminance contrasts relative to their chromatic counterparts. A plausible view is that this phenomenon is related to the magnocellular-parvocellular distinction. In general, the presence of frequency-doubling and other harmonic distortions may preclude the scalp-recorded steady-state VEP to suprathreshold luminance contrasts from describing accurately the spatiotemporal transfer characteristics of the human visual system.