Psychophysical relationships among mechanisms sensitive to pattern, motion and flicker

Abstract

Sensitivity to drifting gratings was measured both before and after adaptation to a uniform flickering field. In the first experiment, it was found that viewing uniform flicker with one eye impaired sensitivity for drifting gratings presented to the same or contralateral eye. Likewise, adaptation to drifting gratings increased flicker detection thresholds. In the second experiment, temporal tuning of the adaptation effect was determined by adapting observers to several different flicker frequencies and testing with gratings of different drift rate. The data suggested the existence of broadly tuned temporal channels which respond to both flicker and motion. In a third experiment, spatial tuning of uniform flicker adaptation was evaluated by employing test gratings of different spatial frequency. The threshold elevation curves were low-pass in shape and exhibited an upper cut-off at 3–4 c/deg. Moreover, the 3–4 c/deg limit was found even when observers explicitly set thresholds for detecting temporal change. The results of the three experiments are consistent with the view that the human visual system contains separate sustained and transient mechanisms. Contrary to previous suggestions that the two systems play specialized roles in perception, however, our data indicate that both transient and sustained mechanisms can signal motion.