Orientation anisotropy of visual stimuli in rhesus monkey: a behavior study

The contrast sensitivity of the rhesus monkey was tested, according to a modified reaction-time paradigm, for sine-wave grating targets at different orientations. The monkey possesses an oblique effect slightly larger than that of humans. A reaction time analysis showed the oblique effect to be a suprathreshold as well as a threshold phenomenon. The presence of this effect further strengthens the use of the monkey as a model for the human visual system.