Multiple Spatial-Frequency Tuning of Electrical Responses from Human Visual Cortex*

Summary. Human occipital potentials evoked by stimulation with a counterphase flickering grating were recorded by a digital narrowband filter technique. The data showed a surprising degree of narrow tuning to particular spatial frequencies in addition to the expected narrow temporal frequency tuning. At each temporal frequency, there could be two or more peaks of response to different spatial frequencies, each distinct from the whole field flicker response. Variations in this multiple spatial frequency tuning were investigated as a function of luminance, electrode location, and temporal frequency for several observers. The results are interpreted in terms of many stimulus-specific resonant neural circuits within the brain, and suggest that it is possible to make a highly detailed exploration of the responses of neural circuits to visual stimulation. Key words: VEP- Pattern- Spatial frequency- Cortex. It is often tacitly assumed that the electrical activity of the brain recorded from the scalp should reflect the properties of the visual system as inferred from psychophysics. This approach is not necessarily the most fruitful, because when a correspondence is obtained, it provides little new information about the visual system that was not already known from the psychophysics. On the other hand, new discoveries, dissimilar from psychophysics, are frequently considered to show some kind of artifact of the electrical activity which is ignored in the description of visual function. We propose to take a rather different approach which may prove more incisive in understanding the electrical activity of the brain, and the visua