Gaze Tracking

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Transcript of Gaze Tracking

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    INTRODUCTION

    If the eyes are the windows to the soul as to quote William Shakespeare,

    then the one of the logical steps to understanding the human behavior and

    motivation should involve the study of eye gaze tracking. When someones eye

    movements are tracked, the path where attention is deployed can be determined.

    Human vision and acuity is one of the most complex systems of the human body

    and is important to human survival. We move our eyes to shift our attention from

    one portion of the visible field to another. In doing so, we can obtain a higher

    resolution where ever direction we direct the central point of our gaze. If we track

    some ones eye movement we can follow the path of their attention.

    The other appropriate words to describe the meaning of the word gaze are

    look, glare, stare, glimpse etc. Thus gaze tracking is detecting and analyzing the

    position that a user is looking at. A wide variety of disciplines has its application,

    including cognitive science, psychology (notably psycholinguistics, the visual

    world paradigm), human-computer interaction (HCI), video conferences

    marketing research and medical research (neurological diagnosis). Using eye gaze

    trackers as a selection tool is necessary too for people with disabilities where eye

    movements may be the only body movement over which the person has control.

    Marketing and commercial uses could provide information on what sort of

    packaging may attract more attention or what aspects of commercials or

    marketing strategies are successful. More recently, there has been growth in using

    eye tracking to study how users interact with different computer interfaces.

    Specific questions researchers ask are related to the how easy different interfaces

    are for users. The results of the eye tracking research can lead to changes in design

    of the interface. Yet another recent area of research focuses on Web development.This can include how users react to drop-down menus or where they focus their

    attention on a Website so the developer knows where to place an advertisement.

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    HISTORY

    In the 1800s, the study of the eye movement was made using direct

    observation. In 1879 in Paris, Louis mile Javal observed that reading does not

    involve a smooth sweeping of the eyes along the text, as previously assumed, buta series of short stops (called fixations) and quick saccades. This observation

    raised important questions about reading, which were explored during the 1900s:

    On which words do the eyes stop? For how long? When does it regress back to

    already seen words?

    Fig.1. An example of fixations and saccades over text. This is the typical pattern

    of eye movement during reading. The eyes never move smoothly over still text.

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    Edmund Huey built an early eye tracker, using a sort of contact lens with a hole

    for the pupil. The lens was connected to an aluminum pointer that moved in

    response to the movement of the eye.

    In the 1950s, Alfred L. Yarbus did important eye tracking research and his

    1967 book is very highly quoted. He showed the task given to a subject has a very

    large influence on the subject's eye movement.

    He also wrote about the relation between fixations and interest: "All the

    records ... show conclusively that the character of the eye movement is either

    completely independent of or only very slightly dependent on the material of the

    picture and how it was made, provided that it is flat or nearly flat."

    Fig.2. This study by Yarbus (1967) is often referred to as evidence on how the

    task given to person influences his or her eye movement.

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    The cyclical pattern in the examination of pictures "is dependent not only

    on what is shown on the picture, but also on the problem facing the observer and

    the information that he hopes to gain from the picture."

    The 1980s also saw the birth of using eye tracking to answer questions

    related to human-computer interaction. Specifically, researchers investigated how

    users search for commands in computer menus. Additionally, computers allowed

    researchers to use eye-tracking results in real time, primarily to help disabled

    users.

    According to Hoffman, current consensus is that visual attention is always

    slightly (100 to 250 ms) ahead of the eye. But as soon as attention moves to a new

    position, the eyes will want to follow. We still cannot infer specific cognitive

    processes directly from a fixation on a particular object in a scene. For instance, a

    fixation on a face in a picture may indicate recognition, liking, dislike, puzzlement

    etc. Therefore eye tracking is often coupled with other methodologies, such as

    introspective verbal protocols.

    GAZE TRACKER TYPES

    Camera-vision-based gaze-tracking methods can be categorized into two

    types: the wearable-camera- based method and the remote-camera-based

    method. The former method is called the head-mounted gaze-tracking method

    and requires the user to wear a device consisting of a camera to capture the eye

    image of the user at a close distance.

    Light, typically infrared, is reflected from the eye and sensed by a video

    camera or some other specially designed optical sensor. The information is then

    analyzed to extract eye rotation from changes in reflections. Video based eyetrackers typically use the corneal reflection (the first Purkinje image) and the

    center of the pupil as features to track over time. A more sensitive type of eye

    tracker, the dual-Purkinje eye tracker, uses reflections from the front of the cornea

    (first Purkinje image) and the back of the lens (fourth Purkinje image) as features

    to track. A still more sensitive method of tracking is to image features from inside

    the eye, such as the retinal blood vessels, and follow these features as the eye

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    rotates. Optical methods, particularly those based on video recording, are widely

    used for gaze tracking and are favored for being non-invasive and inexpensive.

    In the Head-mounted-display (HMD)-based eye tracking devices light

    illuminators at the corners of the monitor and the helmet-type device consisting of

    the camera for capturing an eye image. The Head-mounted-display (HMD)-based

    eye tracking devices in which, it is not necessary to consider the facial movement

    since the HMD moves according to the facial movement of the user. However, if

    the HMD is moved or slipped down from its initial wearing status of the user-

    dependent calibration, the error of gaze estimation increases.

    Next, in the remote-camera-based method, the camera with a zoom lens

    captures the users eye. It is even more convenient for the users because they do

    not need to wear any devices.

    Each method of gaze tracking has advantages and disadvantages, and the

    choice of an eye tracking system depends on considerations of cost and

    application. There are offline methods and online procedures like Attention

    Tracking. There is a trade-off between cost and sensitivity, with the most sensitive

    systems costing many tens of thousands of Eye tracking 6 dollars and requiring

    considerable expertise to operate properly. Advances in computer and videotechnology have led to the development of relatively low cost systems that are

    useful for many applications and fairly easy to use. Interpretation of the results

    still requires some level of expertise, however, because a misaligned or poorly

    calibrated system can produce wildly erroneous data.

    With the increase in the number of gaze-tracking applications, various

    researches on gaze tracking have been carried out in order to improve accuracy

    and user convenience, reducing processing time and simplifying the complicated

    stage of calibration.

    DATA REPRESENTATION

    To allow interpretation of the data that is recorded by the various types of

    eye trackers exist various software that animates or visually represents it, so that

    the visual behavior of one or more users can be graphically resumed. The

    following ones are the most commonly used:

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    Animated representations of a point on the interface: This method is used

    when the visual behavior is examined individually indicating where did the user

    focus his/her gaze in each moment, complemented with a small path that indicates

    the previous saccade movements, as seen in the image.

    Static representations of the saccade path: This is fairly similar to the one

    described above with the difference that this is static method. A higher level of

    expertise than with the animated ones is required to interpret this.

    Heat maps: An alternative static representation, mainly used for the agglomerated

    analysis of the visual exploration patterns in a group of users, differing from both

    methods explained before. In these representations, the hot zones or zones with

    higher density designate where the users focused their gazes with a higher

    frequency.

    Blind zones maps: This method is a simplified version of the Heat maps where

    the visually less attended zones by the users are displayed clearly, thus allowing

    for an easier understanding of the most relevant information, that is to say,