The Effects of Transient Adaptation on VDT Operations

Abstract

The purpose of this study was to investigate the effects of transient adaptation in a simulated VDT operation. Specifically, the study attempted to determine transient adaptational effects that may result in visibility losses or decrements in visual performance, when an observer shifts his or her point of regard from a region of higher overall luminance (e.g., a negative contrast source document with dark characters on a light background) to a region of lower overall luminance (e.g., a positive contrast video display with light characters on a dark background), and vice versa. The source document and VDT display were simulated using a back-projection, free-viewing apparatus. The luminance shifts made up the two transient conditions: a downward change in luminance level (i.e., negative to positive contrast displays), and an upward change in luminance level (i.e., positive to negative contrast displays). The results of these two transient state conditions were compared to two steady state conditions in which there was no change in luminance level or flash contrast thresholds (i.e., Sloan-Snellen test-letter flash was superimposed on the display) were determined using the up-and-down psychophysical method combined with the forced-choice technique and knowledge of results. The ratio of the transient state contrast threshold to the steady state contrast threshold served as an index of visibility loss. The goal of the research due to transient adaptation in VDT operations, but to also determine possible advantages and disadvantages of positive vs. negative contrast video displays.