Off-line and On-line Stress Detection Through Processing of the Pupil Diameter Signal

Abstract

The pupil diameter (PD), controlled by the autonomic nervous system, seems to provide a strong indication of affective arousal, as found by previous research, but it has not been investigated fully yet. In this study, new approaches based on monitoring and processing the PD signal for off-line and on-line "relaxation" vs. "stress" differentiation are proposed. For the off-line approach, wavelet denoising, Kalman filtering, data normalization, and feature extraction are sequentially utilized. For the on-line approach, a hard threshold, a moving average window and three stress detection steps are implemented. In order to use only the most reliable data, two types of data selection methods (paired t test based on galvanic skin response (GSR) data and subject self-evaluation) are applied, achieving average classification accuracies up to 86.43 and 87.20% for off-line and 72.30 and 73.55% for on-line algorithms, with each set of selected data, respectively. The GSR was also monitored and processed in our experiments for comparison purposes, with the highest classification rate achieved being only 63.57% (based on the off-line processing algorithm). The overall results show that the PD signal is more effective and robust for differentiating "relaxation" vs. "stress," in comparison with the traditionally used GSR signal.

Optimal timing of retinal scanning during dark adaptation, in the presence of fixation on a target: the role of pupil size dynamics

“…18,19 Other studies have shown that pupil size can also be affected by the level of arousal, 20 the transient allocation of attention during which the pupil shows transient dilation, 21,22 a type of stress reaction. 23 Yet, since our study deals with the progression of relative changes with respect to a light-adapted baseline, we believe that we have observed a clear pattern of a relatively fast initial increase, and then a slower decrease in pupil size, as long as the arousal factor was controlled and fixation was present.…”

Clinical experimental stress studies: methods and assessment

“…The pupil can constrict to 1.5 mm in diameter or dilate to about 8-9 mm depending on the predominant activation of parasympathetic or sympathetic nervous system. Since an increase in the sympathetic activity promotes pupil dilation (Bradley et al, 2008), pupil dilation has also been employed as a physiological marker of sympathetic nervous activation and stress induction (Yamanaka and Kawakami, 2009;Ren et al, 2014).…”

Linking numbers to perceptions and experiences: Why we need transdisciplinary mixed-methods combining neurophysiological and qualitative data

“…Another study found that pupil diameter increased when viewing emotional pictures, regardless of their valence, and that this correlated with GSR, suggesting that pupil diameter increase is sympathetically mediated (Bradley et al, 2008). It can also be used for the detection of pain, for instance, in non-communicative patients (Ren et al, 2014). Pupil dilatation can now easily be measured with special glasses or cameras, even in an unobtrusive way (Petridis et al, 2013).…”

“…However, GSR lacks specificity because elevated levels of GSR are not always the result of stress, since other factors (such as temperature) may also result in an increased GSR (Bakker et al, 2011). Therefore, more recently, pupillometry has been proposed as a more effective and robust parameter for detection of stress (Ren et al, 2014).…”