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2003 | Buch

Visual Attention Kapitel lesen Erstes Kapitel lesen

Eye Tracking Methodology: Theory and Practice

verfasst von: Andrew T. Duchowski

Verlag: Springer London

Enthalten in: Professional Book Archive

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Über dieses Buch

The scope of the book falls within a fairly narrow Human-Computer Interac­ tion domain (i. e. , describing a particular input modality), however, it spans a broad range of inter-disciplinary research and application topics. There are at least three domains that stand to benefit from eye tracking research: visual per­ ception, human-computer interaction, and computer graphics. The amalgam­ ation of these topics forms a symbiotic relationship. Graphical techniques pro­ vide a means of generating rich sets of visual stimuli ranging from 2D im­ agery to 3D immersive virtual worlds while research exploring visual atten­ tion and perception in tum influences the generation of artificial scenes and worlds. Applications derived from these disciplines create a powerful Human­ Computer Interaction modality, namely interaction based on knowledge of the user's gaze. Recent advancements in eye tracking technology, specifically the availability of cheaper, faster, more accurate and easier to use trackers, have inspired in­ creased eye movement and eye tracking research efforts. However, although eye trackers offer a uniquely objective view of overt human visual and atten­ tional processes, eye trackers have not yet gained widespread use beyond work conducted at various research laboratories. This lack of acceptance is due in part to two reasons: first, the use of an eye tracker in an applied experimen­ tal setting is not a widely taught subject. Hence, there is a need for a book that may help in providing training.

Inhaltsverzeichnis

Frontmatter

Introduction to the Human Visual System (HVS)

Frontmatter
1. Visual Attention
Abstract
In approaching the topic of eye tracking, we first have to consider the motivation for recording human eye movements. That is, why is eye tracking important? Simply put, we move our eyes to bring a particular portion of the visible field of view into high resolution so that we may see in fine detail whatever is at the central direction of gaze. Most often we also divert our attention to that point so that we can focus our concentration (if only for a very brief moment) on the object or region of interest. Thus, we may presume that if we can track someone’s eye movements, we can follow along the path of attention deployed by the observer. This may give us some insight into what the observer found interesting, i.e., what drew their attention, and perhaps even provide a clue as to how that person perceived whatever scene s/he was viewing.
Andrew T. Duchowski
2. Neurological Substrate of the HVS
Abstract
Considerable information may be gleaned from the vast neuroscientific literature regarding the functionality (and limitations) of the Human Visual System (HVS). It is often possible to qualitatively predict observed psychophysical results by studying the underlying visual “hardware”. For example, visual spatial acuity may be roughly estimated from knowledge of the distribution of retinal photoreceptors. Other characteristics of human vision may also be estimated from the neural organization of deeper brain structures.
Andrew T. Duchowski
3. Visual Psychophysics
Abstract
Given the underlying physiological substrate of the Human Visual System, measurable performance parameters often (but not always!) fall within ranges predicted by the limitations of the neurological substrate. Visual performance parameters, such as visual acuity, are often measured following established experimental paradigms, generally derived in the field of psychophysics (e.g., Receiver Operating Characteristics, or ROC paradigm, is one of the more popular experimental methods).
Andrew T. Duchowski
4. Taxonomy and Models of Eye Movements
Abstract
Almost all normal primate eye movements used to reposition the fovea result as combinations of five basic types: saccadic, smooth pursuit, vergence, vestibular, and physiological nystagmus (miniature movements associated with fixations) (Robinson, 1968). Vergence movements are used to focus the pair of eyes over a distant target (depth perception). Other movements such as adaptation and accommodation refer to non-positional aspects of eye movements (i.e., pupil dilation, lens focusing). With respect to visual display design, positional eye movements are of primary importance.
Andrew T. Duchowski

Eye Tracking Systems

Frontmatter
5. Eye Tracking Techniques
Abstract
The measurement device most often used for measuring eye movements is commonly known as an eye tracker. In general, there are two types of eye movement monitoring techniques: those that measure the position of the eye relative to the head, and those that measure the orientation of the eye in space, or the “point of regard” (Young & Sheena, 1975). The latter measurement is typically used when the concern is the identification of elements in a visual scene, e.g., in (graphical) interactive applications. Possibly the most widely applied apparatus for measurement of the point of regard is the video-based corneal reflection eye tracker. In this chapter, most of the popular eye movement measurement techniques are briefly discussed first before covering video-based trackers in greater detail.
Andrew T. Duchowski
6. System Hardware Installation
Abstract
Several types of eye trackers are available, ranging from scleral coils, EOG, to video-based corneal reflection eye trackers. While each has its benefits and drawbacks (e.g., accuracy vs. sampling rate), for graphical or interactive applications the video-based corneal reflection tracker is arguably the most practical device. These devices work by capturing video images of the eye (illuminated by an infra-red light source), processing the video frames (at video frame rates) and outputting the eye’s x- and y-coordinates relative to the screen being viewed. The x- and y-coordinates are typically either stored by the eye tracker itself, or can be sent to the graphics host via serial cable. The advantage of the video-based eye tracker over other devices is that it is relatively noninvasive, fairly accurate (to about 1° visual angle over a 30° viewing range), and, for the most part, not difficult to integrate with the graphics system. The video-based tracker’s chief limitation is its sampling frequency, typically limited by the video frame rate, 60Hz. Hence, one can usually expect to receive eye movement samples at least every 16ms (typically a greater latency should be expected since the eye tracker needs time to process each video frame, and the graphics host needs time to update its display).
Andrew T. Duchowski
7. System Software Development
Abstract
In designing a graphical eye tracking application, the most important requirement is mapping of eye tracker coordinates to the appropriate application program’s reference frame. The eye tracker calculates the viewer’s Point Of Regard (POR) relative to the eye tracker’s screen reference frame, e.g., a 512 × 512 pixel plane, perpendicular to the optical axis. That is, for each eye, the eye tracker returns a sample coordinate pair of x- and y-coordinates of the POR at each sampling cycle (e.g., once every ~16ms for a 60Hz device). This coordinate pair must be mapped to the extents of the application program’s viewing window.
Andrew T. Duchowski
8. System Calibration
Abstract
Currently, most video-based eye trackers require calibration. This is usually a sequence of simple stimuli displayed sequentially at far extents of the viewing region. The eye tracker calculates the Point Of Regard (POR) by measuring the relative observed position of the pupil and corneal reflection at these locations, and then (most likely) interpolates the POR value at intermediate eye positions. The individual stimuli used for this purpose are simple white dots or cross-hairs on a black background. In cases where the eye tracker is used in an outside setting (e.g., for use during driving or while walking outside the lab), calibration marks may be made from simple targets such as tape or other visible markers fixed to objects in the environment. The purpose of calibration is to present a sequence of visible points at fairly extreme viewing angle ranges (e.g., upper-left, upper-right, lower-left, lower-right). These extrema points should be chosen to provide a sufficiently large enough coordinate range to allow the eye tracker to interpolate the viewer’s POR between extrema points. Most (video-based) eye trackers provide built-in calibration techniques where a number of such extrema points (e.g., 3, 5, or 9 typically) are presented in order.
Andrew T. Duchowski
9. Eye Movement Analysis
Abstract
The goal of eye movement measurement and analysis is to gain insight into the viewer’s attentive behavior. As can be seen in Figure 8.5 at the end of Chapter 8, raw eye movement data, or perhaps data processed to a certain extent such as Gaze Intersection Point (GIP) data in Virtual Reality, may appear to be informative, however, without further analysis, raw data is for the most part meaningless. While intuitively (and from the knowledge of the task), it is possible to guess where the subject happened to be paying attention in the environment (over the internal calibration points, as s/he was instructed), it is not possible to make any further quantitative inferences about the eye movement data without further analysis. A method is needed to identify fixations—those eye movements which best indicate the locations of the viewer’s (overt) visual attention.
Andrew T. Duchowski

Eye Tracking Applications

Frontmatter
10. Diversity and Types of Eye Tracking Applications
Abstract
A wide variety of eye tracking applications exist, which can broadly be described within two categories, termed here as diagnostic or interactive. In its diagnostic role, the eye tracker provides objective and quantitative evidence of the user’s visual and (overt) attentional processes. As an interface modality, the eye tracker serves as a powerful input device which can be utilized by a host of visually-mediated applications.
Andrew T. Duchowski
11. Neuroscience and Psychology
Abstract
A wide assortment of eye tracking studies can be found in the increasingly related fields of Neuroscience and Psychology. Topics range from basic re?search in vision science to the investigation of visual exploration in aesthetics (e.g., perception of art). A useful approach to navigating through vast collections of early and contemporary literature is to (for the outset) dissociate high-level cognitive studies from those concerned with a low-level functional view of the brain. In this sense, to use a computational analogy, one can distin?guish between the “hardware” (low-level brain circuitry) on which the “software” (high-level cognition) functions. In a complimentary view of the apparently disparate disciplines, neuroscience identifies the physiological components which are ultimately responsible for perception. In the context of vision and eye movements, knowledge of the physiological organization of the optic tract as well as of cognitive and behavioral aspects of vision is indispensable in obtaining a complete understanding of human vision.
Andrew T. Duchowski
12. Industrial Engineering and Human Factors
Abstract
Eye tracking offers a unique measure of human attentional behavior. This is particularly important in evaluating present and future environments in which humans do and will work. The examination of human interaction and behavior within their environments, particularly ones in which humans often perform functions critical to safety, is one topic studied by human factors and industrial engineers. Traditional measurement methods of human performance often include measures of reaction time and accuracy, e.g., how fast a person completes a task and how well this task is performed. These are generally measures associated with performance. To study the steps taken to perform the tasks requires analysis of the individual procedures performed. For this analysis, process measures are often needed. Eye movements are particularly interesting in this latter context since they present measures which can provide insights into the visual, cognitive, and attentional aspects of human performance.
Andrew T. Duchowski
13. Marketing/Advertising
Abstract
Eye tracking can aid in the assessment of ad effectiveness in such applications as copy testing in print, images, video, or graphics, and in disclosure research involving perception of fine print within print media and within available tele?vision and emerging High Definition TV (HDTV) displays.
Andrew T. Duchowski
14. Computer Science
Abstract
This chapter gives an overview of primarily interactive applications mainly developed by computer science researchers. Following the hierarchy of eye tracking systems given earlier, apart from diagnostic usability studies, this chapter focuses on two types of interactive applications: selective and gaze-contingent. The former approach uses an eye tracker as an input device, similar in some ways to a mouse. This type of ocular interaction is often studied by researchers involved in the fields of Human-Computer Interaction (HCI) and Computer-Supported Collaborative Work (CSCW). The latter gaze-contingent application is a type of display system wherein the information presented to the viewer is generally manipulated to match the processing capability of the Human Visual System, often matching foveo-peripheral perception in real-time. It should be noted that a good deal of previous work discussed in this chapter is based on conference proceedings.
Andrew T. Duchowski
15. Conclusion
Abstract
Eye tracking has sometimes been referred to as a technology in search of an application. Through the presentation of examples in this text, which is by no means exhaustive, it appears that many interesting applications have now been found. There is a good deal of opportunity for interesting, meaningful research.
Andrew T. Duchowski
Backmatter
Metadaten
Titel
Eye Tracking Methodology: Theory and Practice
verfasst von
Andrew T. Duchowski
Copyright-Jahr
2003
Verlag
Springer London
Electronic ISBN
978-1-4471-3750-4
Print ISBN
978-1-85233-666-0
DOI
https://doi.org/10.1007/978-1-4471-3750-4