ABSTRACT
The National Research Council (Huey & Wickens, 1993) has identified transitions in task demand as an important dimension of human operator response. The effects of such demand transitions on vigilance performance have been explored in only two published studies (Krulewitz, Warm, & Wohl, 1975; Gluckman, Warm, Dember, & Rosa, 1993). The results of the first study suggested that the effects of transitions in task demand are characterized by simple psychophysical contrast. However, the latter study failed to confirm these results. The present study was designed to further explore whether demand transitions can be adequately described by a psychophysical contrast model. With that goal in mind, observers were shifted from a high salience (low demand) to a low salience (high demand) condition and vice-versa. Results failed to confirm the psychophysical contrast model. However, they did show that transitions in task demand have important implications for task-induced stress.
