Annals of Biomedical Engineering

, Volume 42, Issue 1, pp 162–176 | Cite as

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

  • Peng Ren
  • Armando Barreto
  • Jian Huang
  • Ying Gao
  • Francisco R. Ortega
  • Malek Adjouadi


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.


Autonomic nervous system (ANS) Pupil diameter (PD) Galvanic skin response (GSR) Wavelet denoising Kalman filtering Moving average window Backward differentiation Mathematical morphology 



This work was sponsored by NSF grants HRD-0833093 and CNS-0959985.


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Copyright information

© Biomedical Engineering Society 2013

Authors and Affiliations

  • Peng Ren
    • 1
  • Armando Barreto
    • 2
  • Jian Huang
    • 2
  • Ying Gao
    • 3
  • Francisco R. Ortega
    • 4
  • Malek Adjouadi
    • 2
  1. 1.Biomedical Engineering DepartmentFlorida International UniversityMiamiUSA
  2. 2.Electrical and Computer Engineering DepartmentFlorida International UniversityMiamiUSA
  3. 3.Electrical Engineering DepartmentUniversity of Wisconsin-PlattevillePlattevilleUSA
  4. 4.School of Computing and Information SciencesFlorida International UniversityMiamiUSA

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