Spatial frequency tuning of transient non-oriented units

Thresholds for a vertical test stimulus with a 1.0 octave bandwidth were measured as a function of the spatial frequency of a horizontal flickering cosine mask. Both test and mask were temporally modulated at 8.0 Hz, as low temporal frequencies were found to produce very little masking. Separate experiments were run at each of 10 test frequencies from 0.25 to 8.0 cycles per degree (c/deg) at 0.5 octave intervals. Masking curves thus obtained for each of three subjects were used to compute the spatial frequency sensitivities of three non-oriented mechanisms. Compared to previous masking studies of orientation selective units, non-oriented units have somewhat broader spatial frequency sensitivity curves, in agreement with primate neurophysiology.