Delay perception thresholds in human-computer interaction:: Fundamentals for CSCW-applications

In order to optimise resource allocation in telecommunication networks, it is important to have profound knowledge of the users' subjective perceptions of quality. By means of psychophysical methodology we examined the perception thresholds of a Quality of Service (QoS) parameter represented by the overall delay between sending information and receiving answer when interacting with a computer. The thresholds are at a delay between vocal input and visual response of 115 (+/- 23) ms, and at a delay between click input and visual response of 78 (+/- 14) ms (numbers in brackets stand for the 95% confidence intervals). These two threshold values differ significantly (p = 0.01) from each other, whereas age and gender of the subjects do not exert significant influence on the location of the thresholds.