The human eye has been called the window to the soul. One component of the eye, the pupil, is considered by some psychologists to be the single involuntary indicator of cognitive activity in the human brain. Much research is currently directed toward eyetracking for the purpose of determining the focus of a subject's attention. This information is then used in various HCI applications (e.g., to operate a system GUI visually). Our efforts in this area are quite unique in that the goal is to use the pupil response as a measure of attentiveness to a particular visual task. We first discuss the role of the pupil in this capacity and the feasibility of a system designed to monitor and interpret pupil response relative to specific visual stimuli. We then demonstrate our approach in implementing a machine vision system (PUPILS - PUPil InterLocution System) that endeavors to gauge a subject's degree of attentiveness relative to a specific visual task. Finally, we present the results of initial experiments using PUPILS, discuss the contributions and shortcomings of this initial prototype and expound our plan for continued research in this area.