Test-retest stability of EEG and eye tracking metrics as indicators of variations in user state - an analysis at a group and an individual level

EEG-and eye tracking metrics have been investigated for their potential as indicators of user state in a variety of studies. However, their stability over time has rarely been assessed and findings are reported predominantly on a group level. In this paper, we report a test-retest analysis that aimed to investigate-at group and individual levels-the temporal stability of fixation duration, pupil dilation, and two built-in metrics from the Emotiv EPOC EEG sensor, namely Engagement and Frustration. The retest confirmed the temporal stability of most physiological metrics at the group level. But analysis at an individual level revealed that outcomes differ strongly between and also within individuals from test to retest. The divergent results between individual and group level illustrate that group level findings are of limited value for applications such as adaptive systems requiring individual user state diagnosis.