Date of Award

Fall 1982

Project Type


Program or Major


Degree Name

Doctor of Philosophy


A series of experiments examined the hypothesis that spatial and temporal variation are processed by separate visual mechanisms. The first set of experiments determined that contrast thresholds set using spatial and temporal criteria covaried for counterphase-flickered gratings over a wide range of spatial and temporal frequencies. The two threshold curves appeared more independent when gratings were drifted, but this probably resulted from different patterns of eye movements within the two tasks.

A second set of experiments measured the time-course of adaptation under conditions designed to isolate the two hypothetical mechanisms, in an attempt to record a temporal "fingerprint" characterizing each mechanism. A test-probe procedure was used to determine contrast thresholds over 60 seconds of adaptation rise-time and 128 seconds of decay. Time constants of exponential curves fit to these data showed no pattern which could be related to the two mechanism hypothesis. A corresponding experiment categorized the appearance of near-threshold gratings during adaptation buildup and decay. When corrected for false-alarm rates, the perception of the stimuli were always pattern, or both pattern and flicker, even when a temporal mechanism should have performed the detection. These results uniformly fail to support the two mechanism hypothesis.