Eye tracking

Eye tracking: process of measuring either the point of gaze or the motion of an eye relative to the head. 

An eye tracker is a device for measuring eye positions and eye movement. 

Eye trackers are used on the visual system: in psychology, in psycholinguistics, marketing, as an input device for human-computer interaction, in product design, for assistive and rehabilitative applications such as controlling wheelchairs, robotic arms, and prostheses. 

Methods for measuring eye movement: video images to extract eye position and search coils based on the electrooculogram.

Eye movements show that an observer’s attention is usually held only by certain elements of a picture, reflecting the human thought processes.

An observer’s thought may be followed to some extent from records of eye movement to determine which elements attract the observer’s eye and, consequently, thought, in what order, and how often.

 When changing its points of fixation, the observer’s eye repeatedly returns to the same elements of the picture.

It is felt that visual attention is always slightly (100 to 250 ms) ahead of the eye, and as soon as attention moves to a new position, the eyes will want to follow.

Cognitive processes cannot be inferred directly from a fixation on a particular object in a scene.

AI in eye-tracking tasks and studies yields additional information that may not have been detected by human observers.

Eye tracking detects and measures the movement of the eyes, allowing the study of visual attention, cognitive processes, and user behavior.

Eye tracking can be done using different types of hardware, including specialized cameras, sensors, or infrared light sources that illuminate the eyes.

The eye tracker captures the movements of the eyes by tracking the position of the pupils or other eye features by detecting the reflection or absorption of the infrared light by the eyes.

Software algorithms analyze the gaze points, fixations and saccades to determine where the user is looking.

Visualization data is presented in the form of heatmaps, gaze plots, or other visual representations. Researchers can use this data to evaluate user attention, measure visual engagement, or optimize user interfaces.

Eye tracking has various applications across different fields:

Eye tracking helps designers understand how users interact with products and interfaces, optimizing usability and user experience, by 

measuring visual attention towards ads, packaging, or displays, providing insights into effective marketing strategies.

Eye tracking is used to study cognitive processes, visual perception, attention disorders, in diagnosing certain neurological conditions, such as brain injuries, attention-deficit hyperactivity disorder (ADHD), or autism spectrum disorders.

Eye tracking is used in simulators and virtual reality setups to analyze training effectiveness.

Eye-trackers measure rotations of the eye:

measurement of the movement of an object attached to the eye

optical tracking without direct contact to the eye

measurement of electric potentials using electrodes placed around the eyes.

Eye-attached tracking uses an attachment to the eye, such as a special contact lens with an embedded mirror or magnetic field sensor, and the movement of the attachment is measured with the assumption that it does not slip significantly as the eye rotates. 

This method allows the measurement of eye movement in horizontal, vertical and torsion directions.

Video-oculography uses an eye-tracking head-mounted display. 

Each eye has an LED light source on the side of the display lens, and a camera under the display lens.

The second broad category uses some non-contact, optical method for measuring eye motion. 

Light, typically infrared, is reflected from the eye and sensed by a video camera or some other specially designed optical sensor. 

Video-based eye trackers typically use the corneal reflection and the center of the pupil as features to track over time. 

The  dual-Purkinje eye tracker, uses reflections from the front of the cornea and the back of the lens as features to track. 

A 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 rotates. 

Optical methods with video recording, are widely used for gaze-tracking and are favored for being non-invasive and inexpensive.

As the  eyes are the origin of a steady electric potential field which can also be detected in total darkness and if the eyes are closed electrical poles can be generated by a dipole with its positive pole at the cornea and its negative pole at the retina. 

The electric signal that can be derived using two pairs of contact electrodes placed on the skin around one eye is called Electrooculogram (EOG). 

If the eyes move from the center position towards the periphery, the retina approaches one electrode while the cornea approaches the opposing one, changing the orientation of the dipole and consequently the electric potential field results in a change in the measured EOG signal. 

By analyzing these changes in eye movement can be tracked. 

EOG is useful for measuring saccadic eye movement associated with gaze shifts and detecting blinks. 

EOG allows recording of eye movements even with eyes closed, and can thus be used in sleep research. 

EOG is the method of choice for measuring eye movement in mobile daily-life situations and REM phases during sleep. 

The major disadvantage of EOG is its relatively poor gaze-direction accuracy compared to a video tracker. 

The most widely used current designs are video-based eye-trackers. 

A camera focuses on one or both eyes and records eye movement as the viewer looks at some kind of stimulus. 

Most modern eye-trackers use the center of the pupil and infrared / near-infrared non-collimated light to create corneal reflections, which can be used to compute the point of regard on surface or the gaze direction. 

Eye-tracking setups vary: Some are head-mounted, some require the head to be stable, and some function remotely and automatically track the head during motion. 

Most use a sampling rate of at least 30 Hz.

Eye movements are typically divided into fixations and saccades – when the eye gaze pauses in a certain position, and when it moves to another position, respectively. 

The series of fixations and saccades is called a scanpath. 

Smooth pursuit describes the eye following a moving object. 

Fixational eye movements include microsaccades, which are involuntary saccades that occur during attempted fixation. 

Most information from the eye is made available during a fixation or smooth pursuit, but not during a saccade.

Scanpaths help in analyzing cognitive intent, interest, and salience. 

If the measuring system is table-mounted head movements are prohibited, and the head position is fixed using a bite bar or a forehead support. 

The positions of eye and head, even with constant gaze direction, influences neuronal activity in higher visual areas.

The goal of eye tracking is most often to estimate gaze direction.

Use of eye-tracking techniques: cognitive science; psychology, human-computer interaction, human factors and ergonomics; marketing research and medical research, tracking eye movement in language reading, music reading, human activity recognition, the perception of advertising, playing of sports, distraction detection and cognitive load estimation of drivers and pilots and as a means of operating computers by people with severe motor impairment.

Eye tracking applications include web usability, advertising, sponsorship, package design and automotive engineering. 

Target stimuli may include websites, television programs, sporting events, films and commercials, magazines and newspapers, packages, shelf displays, consumer systems (ATMs, checkout systems, kiosks) and software. 

By examining fixations, saccades, pupil dilation, blinks and a variety of other behaviors, the effectiveness of a given medium or product can be determined.

Eye-tracking offers the ability to analyze user interaction between web  clicks and how much time a user spends between clicks, thereby providing valuable insight into which features are the most eye-catching, which features cause confusion and which are ignored altogether. 

Eye-tracking can assess search efficiency, branding, online advertisements, navigation usability, overall design and many other website components. 

Eye-tracking is used in a variety of different advertising media: Commercials, print ads, online ads and sponsored programs are all conducive to analysis with current eye-tracking technology. 

Eye tracking technology can provide driver drowsiness detection.

Eye tracking could accurately predict chess moves. 

People with severe motor impairment can use eye tracking for interacting with computers.

Eye tracking can be used to control robotic arms and powered wheelchairs, in analysing visual search patterns, and detecting presence of nystagmus and detecting early signs of learning disability by analyzing eye gaze movement during reading.

Eye tracking is used to establish safety by comparing scan paths and fixation duration to evaluate the progress of pilot trainees, for estimating pilots’ skills, for analyzing crew’s joint attention and shared situational awareness.

Eye tracking technology interacts with helmet mounted display systems in military aircraft. 

Eye tracking is also useful for detecting pilot fatigue.

Eye tracking is also used to monitor cognitive load of drivers to detect potential distraction. 

Eye tracking data may indirectly reveal information about a user’s ethnicity, personality traits, fears, emotions, interests, skills, and physical and mental health condition.

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