Study of Flicker by Increment Threshold Technique

Abstract

Increment thresholds of a small test flash are measured with the flashes superposed upon a flickering background stimulus. Instrumentation is described that permits accurate temporal positioning of the test flash within the light-dark cycle of the background field, and allows rapid threshold measurements to be obtained for the test flash in any desired temporal position. It is found that the increment threshold rises with the light phase and falls with the dark and that this undulation in threshold (believed related to “on-responses” in the human visual system) persists even when the luminance of a 30-cps flickering background stimulus is made too low for the flicker to be perceptible. Other experiments are also described and interpreted.