Effects of temporal frequency on the contrast sensitivity of the human accommodation system

Contrast thresholds were determined for the initiation of accommodative responses to drifting sine-wave stimuli (4.1 c/deg) over a range of temporal frequencies (0-14.0 Hz). Accommodation was monitored with a dynamic infrared optometer. Psychophysical detection thresholds were also determined for the same stimuli. A comparison of the contrast thresholds for detection with those for the initiation of accommodation indicates that these two tasks are mediated by mechanisms of comparable sensitivity. Examination of the effects of temporal frequency on the contrast sensitivity of these two visual tasks reveals modest differences in the tuning properties of the underlying sensory mechanisms. Transient mechanisms tuned to intermediate temporal frequencies appear to have a greater role in the initiation of accommodative responses to grating stimuli than in the detection of such stimuli.