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Real-Time Measurement of Pupil Diameter for Quantitative Monitoring of the Autonomic Nervous System

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"Real-Time Measurement of Pupil Diameter for Quantitative Monitoring of the Autonomic Nervous System", (2008)
Joshi, V. and Barreto A.

ABSTRACT: Recent experiments have provided detailed knowledge regarding the control of pupil aperture by both the Sympathetic and the Parasympathetic divisions of the Autonomic Nervous System (ANS). It has become clear that the pupil diameter (PD) is an interesting physiological variable, which could be quantitatively used to explore the function of the ANS in areas such as affective sensing, detection of deception, etc. However, the required real-time measurements of PD are commonly obtained as a secondary measurement from Eye Gaze Tracking (EGT) systems, which, due to their design priorities, provide suboptimal measurements of PD. This report describes our development of a prototype head-mounted system that uses a high-resolution digital camera, two infrared light sources and an optical arrangement including a 50R-50T infrared beamsplitter, to collect sequential pairs of high-resolution images, particularly well suited for the determination of the contour of the pupil and, therefore, its diameter. This is achieved by alternating the infrared illumination setup to capture the infrared reflection from the retina in only one (“bright pupil”) of the images, but not in the other (“dark pupil”). The difference image derived from each pair significantly facilitates the determination of pupil extent and diameter.