Changes of vigilance caused by varying bit rate conditions

Quality aspects of media content are usually assessed by using subjective rating methods where subjects provide active feedback towards the perceived quality. The process how this judgment is being formed and the long-term influences of accompanying physiological processes are not represented by these methods. In this paper we used the electroencephalogram (EEG) to assess the cognitive state (vigilance) of listeners measured by the alpha frequency band power with respect to varying bit rate conditions. We show that stimuli with varying and constant bit rate cause a state of reduced vigilance. In addition we show the potential tendency that an interval of high bit rate audio inserted into a low bit rate stimulus increased the vigilance of listeners at the timescale of minutes. The results show that the perception of degraded media has long-term influences on physiological processes at the time scale of minutes which may influence customer behavior even though it probably stays undetected using purely standard subjective test methods.