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Adaptive Interference Cancelling Removal of Pupillary Light Reflex Contributions in Pupil Diameter Variations

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"Adaptive Interference Cancelling Removal of Pupillary Light Reflex Contributions in Pupil Diameter Variations", (2008)
Gao, Y., Barreto, A. and Adjouadi, M.

ABSTRACT: Under normal circumstances, the pupillary light reflex (PLR) causes the pupil diameter to decrease as larger amounts of light are sensed by the retina. However, the Autonomic Nervous System (ANS) controls the muscles in the iris through both its Sympathetic and Parasympathetic Divisions and modifies the diameter of the pupil in response to other forms of autonomic activation, in addition to light stimulation of the retina. In particular, it has been shown that the pupil diameter also responds to cognitive and emotional processes. We are interested in using the real-time measurement of pupil diameter to assess affective responses during human-computer interaction. However, this will only be possible if signal processing techniques can be used to identify and remove the component of pupil diameter changes due to PLR. In this report, we propose a solution to that prerequisite by practically modeling the PLR system through an Adaptive Interference Canceller (AIC) defined by the changes in measured PD caused exclusively by a step change in illumination, which was simultaneously recorded by a light sensor. Our results confirm that the AIC was able to converge, minimizing its error to acceptable levels. Furthermore, the impulse response model implicitly formed in the weights of the adapted AIC can be extracted as an approximation to the transfer function mediating between changes in illumination and changes of pupil diameter.