Evaluating Eye Tracking Systems for Computer Input

Evaluating Eye Tracking Systems for Computer Input

I. Scott MacKenzie (York University, Canada)
DOI: 10.4018/978-1-61350-098-9.ch015
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Abstract

When a human uses an eye tracker for computer control, the eye is called upon to do ‘double duty’. Not only is it an important sensory input channel, it also provides motor responses to control the computer. This chapter discusses methods of evaluating the interaction. When an eye tracker is used for computer input, how well does the interaction function? Can common tasks be carried out efficiently, quickly, accurately? What is the user’s experience? How are alternative interaction methods evaluated and compared to identify those that work well, and deserve further study, and those that work poorly, and should be discarded? These are the sorts of questions that can be answered with a valid and robust methodology for evaluating eye trackers for computer input.
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Introduction

The eye is a perceptual organ. In the normal course of events, the eye receives sensory stimuli from the environment. The stimuli are processed in the brain as ‘information’ and decisions are formulated on appropriate actions. The normal course of events also calls for the human's decisions to yield motor responses that effect changes in the environment. If the environment is a machine or computer, then the sensory stimuli come from displays and the motor responses act on controls. This scenario mirrors the classical view of the human–machine interface.

Figure 1 provides a diagram.

Figure 1.

Classical view of the human–machine interface (Chapanis, 1965, p. 20)

Although visual displays are the most common, it is also valid to speak of ‘auditory displays’ or ‘tactile displays’. These are outputs from the machine or computer that stimulate the human sense of hearing or touch, respectively. Human motor responses come by way of our fingers, hands, arms, legs, feet, and so on, and are used to control the machine or computer. Of course, speech and articulated sounds are also human responses and may act as controls to issue commands to the computer or machine. They are motor responses since the sound originates through movement in a human’s larynx, or voice box.

Today, computing technology is pervasive and ubiquitous. Computers are used by humans for work and pleasure, in tasks both complex and trivial, and for pursuits mundane, challenging, and creative. Eye trackers are just one example of a computing technology that offers tremendous potential for humans. Applications for eye trackers can be divided along two lines. In one application, an eye tracker is a passive instrument that measures and monitors the eyes to determine where, and at what, the human is looking. In another, the eye tracker is an active controller that allows a human, through his or her eyes, to interact with and control a computer. When a human uses an eye tracker for computer control, the ‘normal course of events’ changes considerably. The eye is called upon to do ‘double duty’, so to speak. Not only is it an important sensory input channel, it also provides motor responses to control the computer. A revised diagram of the human–computer interface is shown in Figure 2. The normal path from the human to the computer is altered. Instead of the hand providing motor responses to control the computer through physical devices (set in grey), the eye provides motor responses that control the computer through ‘soft controls’ – virtual or graphical controls that appear on the system's display.

Figure 2.

The human–computer interface. With an eye tracker, the eye serves double duty, processing sensory stimuli from computer displays and providing motor responses to control the system

This chapter is focused on the second of these two applications – the use of an eye tracker for computer input. Our concern is with methods of evaluating the interaction. When an eye tracker is used for computer input, how well does the interaction function? Can common tasks be carried out efficiently, quickly, accurately? What is the user's experience? How are alternative interaction methods evaluated and compared to identify those that work well, and deserve further study, and those that work poorly, and should be discarded? These are the sorts of questions that can be answered with a valid and robust methodology for evaluating eye trackers for computer input.

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Computer Input

As a computer input device, an eye tracker emulates a computer mouse. Much as point-select operations with a mouse do, the eye can ‘look-select’ and thereby activate soft controls, such as buttons, icons, links, or text. Evaluating eye trackers for computer input, therefore, requires a methodology that addresses both the conventional issues for computer input using a mouse and the unique characteristics of the eye and the eye tracking apparatus.

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