Spatial frequency selectivity of periodic complex cells in the visual cortex of the cat

The spatial frequency selectivity curves for periodic complex cells have been determined using moving sine-wave gratings, and the results have been compared to the Fourier transform of the receptive field excitability profile as determined with a single narrow moving slit.

Abstract

The spatial frequency selectivity curves for periodic complex cells have been determined using moving sine-wave gratings, and the results have been compared to the Fourier transform of the receptive field excitability profile as determined with a single narrow moving slit. These complex cells may respond to moving gratings with a modulated discharge at the temporal frequency of the test grating superimposed on an unmodulated or steady level of activity. The unmodulated level of activity indicates a non-linear process, as does the presence in some parts of the spatial frequency spectrum of modulated components with large second and third harmonic distortions. If tuning curves are plotted based upon levels of modulated activity, then two distinct spatial frequency bands are defined; a broadly tuned band of low spatial frequencies with a full bandwidth of over one octave and a narrowly tuned band of high spatial frequencies with a full bandwidth at half-amplitude of just under one-half octave. The results in the broad-band range cannot be predicted from the Fourier transform of the excitability profile; however, there may be good agreement in the narrow-band range. On the other hand, if tuning curves are plotted on the basis of mean levels of activity, then only a single broadly tuned curve is defined peaking about one octave below the narrow-band spatial frequency.