Computer System Response Time and Psychophysiological Stress II *

Abstract

With the advent of time-shared interactive systems, the psychological impact of system response time (SRT) and SRT variability (SRTV) has become an important issue. Carbonell, et. al. (1968) have suggested that both SRT and SRTV may influence system user performance and satisfaction. A number of studies have been reported that address this issue, but results have been mixed.

In this experiment, twenty subjects (Ss) executed keyboard entries to control the temperature of a simulated industrial process via time-shared process control computer. Temperature was displayed in analog form on a CRT. The task was to maintain the temperature within upper and lower bounds that were clearly indicated on the display. The experimental design consisted of repeated measures with SRT and SRTV as experimental factors. Three SRT's were employed (2, 6 and 10 seconds) with two levels of SRTV (σ² = 0 and σ² = 0.33 seconds). Mean blood pressure (MBP) and heart rate (HR) were continuously monitored during experimental conditions. Task errors were defined as temperature excursions beyond the displayed bounds.

Significant main effects were not obtained for MBP or HR. Significant differences for error rate (performance) were noted for SRT (F(2, 15) = 23.10, p < .05), subjects x SRT (F37, 15) = 1.66, p < .001), and SRT x SRTV (F(1, 15) = 13.14, p < .05). Error data are consistent with the Carbonell et. al. suggestion that long and variable SRT may affect user performance. The results are discussed in terms of their incongruity with current literature.

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