Editing Eye tracking (section)

== Practice ==
A great deal of research has gone into studies of the mechanisms and dynamics of eye rotation, but the goal of eye tracking is most often to estimate gaze direction. Users may be interested in what features of an image draw the eye, for example. The eye tracker does not provide absolute gaze direction, but rather can measure only changes in gaze direction. To determine precisely what a subject is looking at, some calibration procedure is required in which the subject looks at a point or series of points, while the eye tracker records the value that corresponds to each gaze position. (Even those techniques that track features of the retina cannot provide exact gaze direction because there is no specific anatomical feature that marks the exact point where the visual axis meets the retina, if indeed there is such a single, stable point.) An accurate and reliable calibration is essential for obtaining valid and repeatable eye movement data, and this can be a significant challenge for non-verbal subjects or those who have unstable gaze.

Each method of eye-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 [[AttentionTracking]]. There is a trade-off between cost and sensitivity, with the most sensitive systems costing many tens of thousands of dollars and requiring considerable expertise to operate properly. Advances in computer and video technology have led to the development of relatively low-cost systems that are useful for many applications and fairly easy to use.<ref>{{cite journal |doi=10.1155/2016/8680541|pmid=27034653|pmc=4808529|title=Low Cost Eye Tracking: The Current Panorama|journal=Computational Intelligence and Neuroscience|volume=2016|pages=1–14|year=2016|last1=Ferhat|first1=Onur|last2=Vilariño|first2=Fernando|doi-access=free }}</ref> Interpretation of the results still requires some level of expertise, however, because a misaligned or poorly calibrated system can produce wildly erroneous data.

=== Eye-tracking while driving a car in a difficult situation ===
[[Image:Eye movements of drivers.jpg|upright=1.5| thumb| right |Frames from narrow road eye tracking described in this section<ref>{{harvnb|Hunziker|2006}}. Based on data from: Cohen, A. S. (1983). Informationsaufnahme beim Befahren von Kurven, Psychologie für die Praxis 2/83, Bulletin der Schweizerischen Stiftung für Angewandte Psychologie.</ref>]]

The eye movement of two groups of drivers have been filmed with a special head camera by a team of the Swiss Federal Institute of Technology: Novice and experienced drivers had their eye-movement recorded while approaching a bend of a narrow road. The series of images has been condensed from the original film frames<ref>Cohen, A. S. (1983). Informationsaufnahme beim Befahren von Kurven, Psychologie für die Praxis 2/83, Bulletin der Schweizerischen Stiftung für Angewandte Psychologie</ref> to show 2 eye fixations per image for better comprehension.

Each of these stills corresponds to approximately 0.5 seconds in real time.

The series of images shows an example of eye fixations #9 to #14 of a typical novice and of an experienced driver.

Comparison of the top images shows that the experienced driver checks the curve and even has Fixation No. 9 left to look aside while the novice driver needs to check the road and estimate his distance to the parked car.

In the middle images, the experienced driver is now fully concentrating on the location where an oncoming car could be seen. The novice driver concentrates his view on the parked car.

In the bottom image the novice is busy estimating the distance between the left wall and the parked car, while the experienced driver can use their [[peripheral vision]] for that and still concentrate vision on the dangerous point of the curve: If a car appears there, the driver has to give way, i.e. stop to the right instead of passing the parked car.<ref>Pictures from {{harvnb|Hunziker|2006}}</ref>

More recent studies have also used head-mounted eye tracking to measure eye movements during real-world driving conditions.<ref>{{cite journal |last1=Grüner |first1=M |last2=Ansorge |first2=U |title=Mobile eye tracking during real-world night driving: A selective review of findings and recommendations for future research |journal=Journal of Eye Movement Research |date=2017 |volume=10 |issue=2 |pmid=33828651| doi=10.16910/JEMR.10.2.1|pmc=7141062 |doi-access=free }}</ref><ref name="bop.unibe.ch"/>

=== Eye-tracking of younger and elderly people while walking ===
While walking, elderly subjects depend more on [[fovea centralis|foveal]] vision than do younger subjects. Their walking speed is decreased by a limited [[visual field]], probably caused by a deteriorated peripheral vision.

Younger subjects make use of both their central and peripheral vision while walking. Their peripheral vision allows faster control over the process of walking.<ref>{{Cite journal | doi=10.2466/pms.2002.94.3c.1283| pmid=12186250|title = Comparative Study of Eye Movements in Extent of Central and Peripheral Vision and Use by Young and Elderly Walkers| journal=Perceptual and Motor Skills| volume=94| issue=3_suppl| pages=1283–1291|year = 2002|last1 = Itoh|first1 = Nana| last2=Fukuda| first2=Tadahiko| s2cid=1058879}}</ref>