ABSTRACT
I. INTRODUCTION This chapter describes the design of an instrument usually known as the dual Purkinje image (DPI) eyetracker, sometimes as the Purkinje image eyetracker, or even just the Purkinje or SRI tracker. This instrument, along with several major accessories, was under continuous development at SRI International (formerly Stanford Research Institute) from 1965 to 1988. During that time the form of the basic instrument passed through five stages-denoted as generations I, II, III, IV, and V. Many eyetracker systems, some arranged in monocular and some in binocular configurations, and including various combinations of accessories, were built at SRI for vision laboratories across the United States and for some abroad. In the fall of 1988 this technology was licensed by SRI to Fourward Technologies,* which has continued its development and marketing.
