Orientation selectivity in cats and humans assessed by masking.

A two-alternative, spatial forced-choice procedure was used to measure contrast thresholds for detection of sinusoidal gratings that appeared within one-dimensional random noise. The orientation of the noise was symmetrically varied relative to the orientation of the test grating to derive estimates of orientation tuning at two spatial frequencies for both cats and humans. For cats, orientation tuning (half-width at half-strength) averaged 23 deg while for humans tuning averaged 28 deg. Both species displayed narrower tuning at the higher spatial frequency. In addition, evidence is presented that estimates of orientation tuning may be narrower when only one orientation of noise is presented, due to "off-channel" detection strategies. These estimates of orientation tuning are discussed in terms of the orientation selectivity of cortical neurons.