Eye-Tracking

Eye- tracking (rarely also: eye tracking or oculography ) refers to the recording of mainly of fixations ( points you look closely ), saccades ( rapid eye movements ), and regressions existing eye movements of a person.

As an eye-tracker equipment and systems are referred to, the recording session and allow an analysis of eye movements.

This eye tracking is used as a scientific method in the neurosciences, perception, cognition and advertising psychology, cognitive or clinical linguistics, product design and reading research. It is also used in the study animals, in particular in connection with the investigation of their cognitive abilities.

• 2.4.1 components 2.4.1.1 Installation of the headset
• 2.4.1.2 fine adjustment
• 2.4.1.3 System Configuration

• 2.4.2.1 operations
• 2.4.2.2 missions
• 2.4.2.3 technology

• 3.1 Medicine
• 3.2 Neuroscience
• 3.3 Psychology
• 3.4 Market Research
• 3.5 computer science
• 3.6 Human- Machine Interaction

History

Already in the 19th century eye movements were recorded by direct observation. One of the first was the Frenchman Émile Javal, who described the eye movements during reading.

With the invention, the film camera, it was possible to record the direct observation and subsequently analyzed. This was done in 1905 by Judd, McAllister and Steel.

As the fundamental pioneer of eye tracking with high accuracy applies the Russian ALYarbus, in particular proved the influence of the task on eye movements when viewing pictures.

In the 1970s, then new methods have been developed.

• Retinal afterimages, by a series of strong light stimuli so-called after-images on the retina are generated by their location can be close to the eye movement.
• Electrooculograms measure the voltage between the retina ( negative pole) and the cornea ( positive pole).
• Contact lens method, are coated and the reflection is recorded by a camera.
• Search coil, may be also used in the contact lenses, which are provided with coils and are subjected to a magnetic field. Of the eye movement induced voltage can then be calculated.
• Corneal reflex method, which uses the reflection of one or more light sources ( infrared or special laser ) on the cornea and the pupil position to each other. The eye image is captured with an appropriate camera. The process is also referred to as "video based eye tracking".

Depending on the application, experimental requirements and system performance, a distinction is video-based Blickbewegungsmeßsystemen today mainly between 4 categories.

Recording equipment

Basically, the eye tracker can be divided in two different designs: mobile eye tracker, which are firmly attached to the head of the subject and those that are externally installed. The latter can in turn be divided into two categories: the remote devices as well as those that are connected to a fixation of the head of the subject.

Mobile Systems

Mobile systems, so-called head-mounted eye tracker allow primarily mobility.

Here, the eye tracker, consisting of a mounted eye camera and a camera field of view by means of a special device on the head of the subject. This may vary by manufacturer of various restraint systems or a helmet made ​​. The advantage of this design lies in mobile use when the control computer, a notebook is used, can be transported by the subjects ( for example, in the backpack ) this. While external devices only looking at a screen can be recorded, mobile eye tracker thus are also suitable for field studies outside the laboratory context. The disadvantage of this solution is the non- parameter- data recording. So only the view of the subject appears in a video of his field of view camera. For a statistical analysis must be manually checked with high effort these videos. Applications include market research ( while looking a subject while walking through a supermarket shelf ) or usability (how long a subject looks when driving on the road, how long to the navigation device ).

Evaluations and analyzes are essentially individual and user -centered. A fortified also the head system scene camera records a video that usually corresponds to the field of view of the subject. In this video, the viewing position of the subject is recorded and thus allows online but also in the analysis offline, a pursuit of the visual pathway during a free activity of the subject. Generalization over several subjects and attention analysis on specific objects can be realized technically 3D/6D position detection systems (so-called head tracker ).

External systems

External systems, so remote eye tracker allow the implementation of non-contact measurements. Of this total mechanical components such as transmission cables or chin rest. The subject is free to move after successful calibration within a certain range of motion. An important aspect here is in the compensation of head movements. A person can fix a place and thereby perform head movements without losing the Focus point.

For registration of eye movements on a computer screen, the components of the unit either be installed directly into a monitor or placed under or next to it. The eye camera automatically detects the eye and "followed" this. There is no contact between the subject and the device. This contrasts with the eye tracker in " Tower " construction, the head of the subject is fixed in the device. The latter type is usually more expensive to purchase and for the subject rather uncomfortable, generally provides for more accurate results in a higher frame rate.

Different techniques are used here:

• Pan -tilt systems:

Mechanically moving parts cause the camera to camera optics according to the head movements of the subject. Current systems achieve this measurement rates of up to 120 Hz

• Tilting -mirror systems:

While the camera and lens remain fixed in space allow servo-driven mirror a track of the eye during head movements.

• Fixed -camera systems:

These systems waive any mechanical moving components and achieve the freedom of movement by means of image processing methods.

These variants have compared the mobile construction with the advantage that they record data that are uniquely parameterized and so can be fed to a statistical analysis ( it can therefore be specified in exact values ​​, looked at what at any time the person in which area of the screen has ). While remote eye tracker mainly in the market and media research can be used ( eg, use of websites, eye movement when watching movies ), find the Tower Eye Tracker in neuroscience use (eg research on microsaccades ).

Special shapes

Simple direct records

Before the advent of complex recording devices simple film clips were used, the analysis of the eye movements made ​​possible by analysis of frames in certain cases. They were able to be used where it was sufficient to the points of view up, down, right, left and center to capture. In addition, this had the advantage that the hand movements and the expression could be seen.

Recording with the computer mouse

Modern methods such as AttentionTracking enable eye tracking using the computer mouse or other pointing device. The view points are obtained in the form of mouse clicks.

Example Model " EL II"

The technical design of an eye-tracker is slightly different depending on the model. Nevertheless, there are fundamental similarities: each eye tracker has an eye camera, a field of view camera and an infrared light source.

Components

The system " EL II ' consists of two equipped with appropriate software computers, a " computer program " and an associated " stimulus computer " including monitors and from a headset. At this two side brackets attached to cameras are used to record the eye movements. Another, found above camera is on four - mounted on one of two computers - tuned infrared markers. It is thus possible to record any kind of fixation to images, or actions. This has, inter alia, the purpose that even with head movements of the subject no artifactual view deviations are calculated. This system also provides the ability to detect the reflections in addition to the Corneal movements of the pupil. Also confounding factors such as the muscle tremor may be so excluded.

Mounting of the headset

The respondent, the headband is placed with the cameras. After the above located camera is brought into position. It will do this as accurately as possible set to medium height and average width of one of the two monitors, namely the so-called stimulus monitor. This monitor allows the referential infrared markers mounted on the camera setting. For the correct adjustment of the monitor itself simply either moved or the chair of the subject is adjusted in height.

The two located on the side retaining arms eye cameras are pivoted so that they are not disturbing in view of the subject. You should be at about the height of the tip of the nose and can already be placed in the approximate position for the later recording. The cameras can be adjusted in three dimensions with the arm itself and by means of clamps and set screws.

Fine adjustment

Using the included software, the fine adjustment - are made - the camera orientation and focus. The latter works on the system's integrated automatic threshold setting for the corneal reflection and the pupil illumination.

When calibrating the subjects at the stimulus screen offered random points in a car sequence that move across the screen. The subject is instructed to follow the points with both eyes. After successful calibration, validation follows. This proceeds as the calibration, but the maximum difference of the eye movement is measured in degrees. Here, the experimenter must decide whether the setting is used, or to be readjusted. A once accepted setting can be readjusted repeatedly during the experiment, since each screen mask with a neutral fixation point appears between the individual stimuli. The system itself suggests that better adjusted eye.

System Configuration

Program computer and stimulus computers are connected together by a network cable. The program computer is also connected to the eyes of cameras and infrared markers in combination. On the stimulus computer software to run the presentation of stimuli and the Visual C programming language for programming the experiments. The monitor on which the stimuli are presented, should have a size of 17 inches, as this appears especially for the implementation of read experiments the most appropriate. Using a joystick, the subject can request the next stimulus.

Program and stimulus computers should be placed in a particular spatial position to prevent reflections and unwanted light stimuli during recording. In addition, the program computer should be located with the control monitor outside the field of view of the subject, in order to avoid distraction from the presented stimuli.

The ETD on the ISS

The Eye Tracker was developed for use on the International Space Station, originally from the German Aerospace Center (DLR ). In early 2004, he was promoted as part of the European-Russian space program on the ISS. The device was developed by Dr. Andrew H. Clarke from Vestibular Lab at the Charité in Berlin in cooperation with the company Chronos Vision and mtronix in Berlin and integrated for use in space by Kayser -Threde.

In initial experiments, carried out by Clarke's team, in cooperation with the Moscow Institute of Biomedical Problems ( IBMP ), the ETD for the measurement of Listing's plane - used - a coordinate system for the determination of eye movements relative to the head. The scientific goal was to determine how the Listing's plane changed under different gravity conditions. In particular, the impact of long- term microgravity aboard the ISS and after subsequent return to Earth's gravity was investigated.

The results contribute to the understanding of neural plasticity in vestibular and oculomotor systems.

These experiments began in spring 2004 and continued until the end of 2008 by a number of cosmonauts and astronauts who spent six months on the ISS.

Operations

The study of the orientation of Listing's plane during a long-term space mission is of special interest because the Listing's plane on the ground is apparently influenced by the vestibular system. This can be determined by measuring the head position relative to gravity. The experiment examined the adaptation of the vestibular system of the astronaut during the stay in weightlessness and after returning to Earth. The experiment also seeks to clarify the extent to which the orientation of Listing's plane as a function of the vestibular system adaptation to altered gravity conditions, in particular the gravity changed. A further question is whether the human body during a long space flight compensates for the lack of the vestibular inputs through other mechanisms.

Missions

The ETD came for this study between 2004 and 2008 are used. During six months of experiments, the experiments were repeated in three- week intervals, whereby the adaptation of microgravity could be evaluated. Equivalent measurements were addition in the first weeks performed at each cosmonauts or astronauts after returning to Earth. Meanwhile, the ETD system is a universal instrument on the ISS. Currently it is used by a group of Russian scientists from the Institute of Biomedical Problems, examine the coordination of eye and head movements in microgravity.

Technology

The digital cameras are equipped with high-performance CMOS image sensors and are connected via bi-directional, high-speed digital connections ( 400Mb / s) with the associated processor board of the host PC. In this PCI processor board is the front-end controller architecture which consists of a digital signal processor ( DSP), programmable integrated circuits ( FPGA). These components are programmed so as to allow the pixel-oriented line acquisition and the measurement of the 2D pupil coordinates.

For the task of eye tracking a substantial data reduction is performed by the sensors and the front-end control architecture. Thus, only pre-selected information from the image sensor to the host computer on which the final algorithms and the data storage are performed transmitted. This development eliminates the bottleneck problems of conventional frame-by- frame image processing and allows a significant increase in frame rates.

The control architecture is integrated into a personal computer and enables the visualization of the eyes and of the respective signals and data. An important development feature is the digital storage of all image sequences of the cameras as digital files on removable disks. In this way, the hard disk with the stored eye data, are sent back to Earth after completing the ISS mission. This ensures an extensive and reliable image data analysis in the research laboratory, and minimizes the time required for the experiment to the ISS.

ETD on Earth

Parallel to the implementation of the ETD used in space a commercially applicable version was developed by Chronos Vision, which is used in many European, North American and Asian laboratories for neurophysiological research.

Areas of application

Medicine

The laser treatment of refractive errors owes its success among other things, The use of eye trackers, which ensure that the laser treatment of the cornea to the planned location, and eye movements are monitored. Optionally, the laser is tracked - or switched off until the eye again has the correct position. Other systems are used in the fields of neurology, balance research, oculomotor and eye disorders. Also in psychiatry win eye tracker increasingly important: With you is the hope, characterized in future to enable more reliable and earlier diagnoses (eg, autism or ADHD).

Neuroscience

Eye trackers are used as comparison systems with functional imaging in magnetic resonance imaging (fMRI ), in studies with magnetoencephalography devices (MEG ), or electroencephalography (EEG ) systems.

Psychology

• Image perception

• Motion perception

• Analysis of the learning progress ( training analysis )

Market research

• Package Design
• Point-Of- Sale ( POS)
• Advertising ( print, online analysis, etc. )

Computer science

• Activity detection

Human- Machine Interaction

• Computer controls for physically impaired people by a mouse eyes. In most cases, the cursor point represents the point of view. An interaction is generally triggered by a fixation of an object.