Dichoptic interaction of harmonically related spatial and temporal frequencies.

Steady-state visual evoked potentials were recorded in response to contrast Reprint requests: Dr. Elmar T. Schmeisser, Division of Ocular Hazards, Letterman Army complex (sum of two spatial frequencies) suprathreshold sinusoidal gratings of two and six cycles/degree in a 5 degrees field. Sine mode counterphasing enhances the second temporal harmonic component of the evoked waveform; square mode counterphasing generates a response with essentially all the power at the fundamental temporal frequency. Digital sums of observed responses to simple gratings presented alone had significantly greater amplitudes than any observed response to presented complex gratings. Response amplitudes ranked significantly by condition: binocular greater than dichoptic greater than monoptic. It is concluded that (a) sinusoidal counterphasing stimuli lead to two stimulus events per shift (an observed grating onset and offset), and (b) spatial frequency channels that are harmonically related in 1:3 ratio do not destructively interfere with each other in either monoptic or dichoptic presentation.