Eye Tracking

Abstract

Eye tracking is a process that records eye movements allowing us to determine where an observer is looking at a given time. This information can be recorded and used in offline analysis or as input to real-time applications. Eye trackers measure the physical rotations of the eyes to determine the gaze or gaze direction. The point being focused upon on a screen is called a gaze point. This information can give us insight into what attracted the attention of an observer or what they found interesting [Duchowski, 2003]. Hornof, Cavender, and Hoselton [2003] also refer to the gaze as the vector between the gaze point and the eye. An eye tracker is used to identify the position of the eye in the image. Witzner Hansen and Ji [2010] state that the two main research areas in eye detection and tracking are image localization and gaze estimation. They further divide the eye detection process into three parts: (1) eye detection, (2) interpretation of eye positions in the image and (3) tracking of the eyes between frames. This information makes it possible to determine where an observer is gazing in 3D, the Line of Sight (LOS), or as a 2D point on a plane, which is also referred to as the Point of Regard (POR) [San Agustin Lopez, 2009]. Eye tracking also makes it possible to study how tasks or free-viewing a scene affect the gaze behavior, as seen in Figure 3.1. The left image shows an observer free-viewing a rendered image of the Kalabsha temple scene. The image to the right shows the eye movements of the same observer performing the task of counting the stones in the courtyard. As discussed in Section 2.3, Yarbus [1967] also showed that the instructions given to the observer watching a stimuli strongly influences what is being looked at.