Abstract

Two gratings inclined at a small constant angle Δθ° were superimposed. Recordings were taken from electrodes located over visual cortex while one grating was counterphase-modulated at F₁, Hz and the other at F₂ Hz. The evoked potential included several discrete nonlinear frequency components of frequencies (nF₁ ± mF₂), n and m being integers. These frequencies were very precisely specified; bandwidths were no more than 0.008 Hz. Then the superimposed gratings were rotated bodily around the clock. A cross-modulation component that was independent of spatial phase reached maximum amplitude for horizontal and vertical orientations, fell to minima within 20° of horizontal and vertical, and showed a submaximum at oblique orientations.

© 1986 Optical Society of America