Temporal summation and orientation acuity.

The effect of stimulus exposure time (ET) on the threshold intensity, necessary for fine orientation discrimination was compared with the effect of ET on the detection threshold. Both discrimination and detection performances were studied concurrently in a two-by-two forced choice paradigm. The results suggest the existence of a mechanism with much longer temporal summation for the discrimination of small orientation differences than for the detection of the stimulus. Orientation acuity improves with ET.