Eye Movement Research

Mechanisms, Processes and Applications

J.M. Findlay, R. Walker, R.W. Kentridge

• Publisher: North Holland
• Year: 1995
• Print ISBN: 9780444814739
• eBook ISBN: 9780080531540
• Topic: Psychology
• Subtopic: Neurology
• Index: Psychology

This volume contains selected and edited papers from the 7th European Conference on Eye Movements (ECEM 7) held in Durham, UK on August 31-September 3 1993. The volume is organized as follows: - Invited Lectures, Pursuit and Co-Ordination, Saccade and Fixation Control, Oculomotor Physiology, Clinical and Medical Aspects of Eye Movements, Eye Movements and Cognition, Eye Movements and Language and finally, Displays and Applications.

Displays and applications

Selection By Looking: A Novel Computer Interface And Its Application To Psychological Research

Dave M. Stampe; Eyal M. Reingold Department of Psychology University of Toronto, Toronto, Canada

Abstract

Real time monitoring of a subject’s gaze position on a computer display of response options may form an important element of future computer interfaces. Response by gaze position can also be a useful tool in psychological research, for example in a visual search task.

Experimental tasks reported include visual search, and typing from an alphabetic menu. A lexical decision study revealed gaze response RT to be much more powerful than button press RT and new phenomena including self-correction were observed. Methods of improving response reliability are introduced, including drift correction by dynamic recentering, gaze aggregation, and automated selection.

Keywords

Eye-movements

eye-tracking

computer-interface

control

handicapped

lexical-decision

typing

disabled

visual search

Introduction

Psychological research using eye movements has focused on the study of natural tasks such as reading or problem solving. Typically, gaze position is simply recorded for later analysis, and is incidental to the experimental task. One exception is the gaze- contingent display paradigm, where the displayed stimuli are changed rapidly in response to eye movements in order to present different images to the foveal and peripheral regions of the subject’s visual field (e.g. McConkie and Rayner, 1976). In this paper, we explore the active use of gaze in performance of an experimental task: selection by looking. We investigate implementation and psychophysical issues, and demonstrate tasks which illustrate the unique potential of this paradigm.

In a typical task, the subject’s gaze position is monitored while viewing displays such as those in Figure 1. The subject registers responses or commands by directing his gaze to targets on the screen and holding his gaze until the response is registered. The gaze- response system’s computer processes the eye tracker output in real time to compute gaze position on the screen and detect response events, then modifies the image displayed to the subject in response to the gaze input.

Figure 1 Gaze control displays from two experimental tasks. Left: the lexical decision task display. Sufficient gaze duration on the “WD” or “NWD” response areas registers an appropriate response, and feedback is given by highlighting the selected response. Right: the eye-typing task. Fixating a character will result in it being typed in the upper part of the screen, and feedback is given by a round dot.

The use of control by eye-movement as an aid to handicapped persons is not new (e.g. Laefsky and Roemer, 1978), but such systems have usually been developed with little research into psychophysical or cognitive factors.

Recently, eye movements have been proposed as computer interface devices for normal users (e.g. Jacob, 1991), but despite high expectations, the advantages and limitations of this interface modality have yet to be determined. There are many tasks in which gaze control would be advantageous, for example as an input device when hands are otherwise occupied (Charlier, Sourdille, Behague, and Buquet, 1991).

In this paper, we will discuss some of the advantages of gaze position response, then summarize the practical aspects of implementing gaze response systems. Dynamic recentering will be introduced as a technique to correct for eye tracker drift to prevent response errors. Results from several experimental tasks will be presented that explore implementation issues, demonstrate the methods discussed, and compare response by gaze to more traditional button press responses.

Advantages of Gaze Response in Research

Gaze response is well suited to typical eye movement research tasks such as visual search within pictures or stimulus arrays. Once the search target is found all the subject need do is to continue fixating the target until the response is registered. This is a highly intuitive response method, requiring no training and resulting in fast reaction times. Targets can be selected even when embedded within pictures or dense arrays of distractors. Gaze response acts as a pointer, providing twodimensional input similar to devices such as touch screens, light pens or computer mice. However, these physical input devices require gross motor movements, which may introduce noise into the eye movement record. Verbal responses can be used to implement complex responses paradigms, but are not practical with eye tracking systems that require bite bars or chin rests. Gaze response not only does not exhibit these problems, but actually enhances the eye movement record.

In eye movement research, gaze response can help to disambiguate the temporal relationship between eye movements and responses during task performance. Asynchrony between eye movements and manual or vocal responses is often seen, as eye movements are free to continue with task execution after the motor program for the response is initiated. With gaze response, the temporal relationship between eye movements and responses is clear, since both cannot be performed at once. Task- related fixations (e.g. searching) and response fixations are easily disambiguated during analysis, allowing the eye movement record of sequential (multiple step) tasks to be clearly divided at the gaze responses.

The use of gaze response in eye movement research is likely to reveal new aspects of cognitive processes. It is important to compare gaze response to more classical response methods such as button presses: such a comparison will be reported in this paper for a lexical decision task. The combination of intuitive operation, spatial selection capability and potential for new findings make gaze position response a powerful tool for psychological research.

Implementation Issues

For gaze response to be practical, especially for psychological research, the implementation is critical. The method chosen for detection of gaze responses in the eye movement data must be carefully chosen to prevent unintended responses. In the following discussion we will evaluate the effects of eye tracker performance on response accuracy, and discuss methods for correcting eye tracker drift.

Detecting Gaze Responses

The most natural technique for gaze response is simply to hold gaze on the response area for a critical time period. Subjectively, the subject simply concentrates on a target until the selection response occ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Introduction
• Contributors
• Invited lectures
• Pursuit and co-ordination
• Saccade and fixation control
• Oculomotor physiology
• Clinical and medical aspects of eye movements
• Eye movements and cognition
• Eye movements and language
• Displays and applications
• Author Index
• Subject Index