Monitoring and Processing of the Pupil Diameter Signal for Affective Assessment of a Computer User Ying Gao, Armando Barreto and Malek Adjouadi Department of Electrical and Computer Engineering Florida International University Miami, FL 33174 USA {ygao002, barretoa, adjouadi}@fiu.edu Abstract. The pupil diameter (PD) has been found to respond to cognitive and emotional processes. However, the pupillary light reflex (PLR), is known to be the dominant factor in determining pupil size. In this paper, we attempt to minimize the PLR-driven component in the measured PD signal, through an Adaptive Interference Canceller (AIC), with the H ∞ time-varying (HITV) adaptive algorithm, so that the output of the AIC, the Modified Pupil Diameter (MPD), can be used as an indication of the pupillary affective response (PAR) after some post-processing. The results of this study confirm that the AIC with the HITV adaptive algorithm is able to minimize the PD changes caused by PLR to an acceptable level, to facilitate the affective assessment of a computer user through the resulting MPD signal. Keywords: Pupil diameter (PD), Pupillary light reflex (PLR), Pupillary affective response (PAR), Adaptive Interference Canceller (AIC), H ∞ time- varying (HITV) adaptive algorithm. 1. Introduction Affective Computing, defined as “computing that relates to, arises from, or deliberately influences emotions” by Picard in 1997 [1] requires computers to have the ability to remain aware of their users’ affective states. Therefore, the affective assessment of the computer user has been considered as one of the key challenges to overcome for improvement of the relationship between human and computers. This challenge has been addressed, among other approaches, through the processing of a variety of physiological signals from the computer users, such as the Galvanic Skin Response (GSR), the Blood Volume Pulse (BVP), etc. We are currently studying the possibility of analyzing pupil diameter (PD) variations in the computer user for the detection of affective changes. The human pupil is the variable-size opening in the iris of the eye, through which light passes to the retina. The size of pupil is known to be controlled by two opposing sets of muscles in the iris, the sphincter and dilator pupillae, which are governed by