Glossary

Glossary

Accommodation

Accommodation (eye focusing) means the eye's ability to adjust its focus by the action of the ciliary muscle, which increases the lens focusing power. When this accommodation skill is working properly, the eye can focus and refocus quickly and effortlessly, which is similar to an automatic focus feature on a camera. The ability of the eye to accommodate does decrease with age due to the crystalline lens becoming less flexible.

Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a chronic, progressive, degenerative disorder affecting the motor neuron cells and the motor tracts in the brain and spinal cord. Also called Lou Gehrig's Disease. The disorder causes muscle weakness and atrophy; symptoms commonly appear in middle to late adulthood, with death in two to five years. The cause is unknown, and there is no known cure. In the last phase, the person may only be able to control his or her eyes.

Assistive software

Software that enables a person with special needs to access the computer with more efficiency, effectiveness or satisfaction.

Blink rate

A blink is defined as a reflexive closing and opening of the eye. Blink rate represents the frequency of blinks recorded over a specific time. For EPOG, a blink is the loss of data between fields. Blink rate is used as an indicator of, for example, fatigue, mental workload, and exposure to adverse conditions (e.g. sun, wind, and airborne particles).

Calibration

Calibration is defined as the method by which gaze tracking systems map eye (and sometimes head) positional data captured by the hardware of the system (often video images of the eye) to the actual gaze vector from eye to host personal computer of the end user. This calibration is then used to calculate and translate gaze vectors from the eye of the end user to cursor, pointer or gaze fixation positions on the host computer screen.

Cameramouse

A camera that tracks the movement of the head or a feature on the face to control the computer, e.g. via an on-screen pointer.

Cerebral Palsy (CP)

Cerebral Palsy (CP) is the term used to describe a group of chronic conditions affecting body movement and muscle coordination. It is usually caused by brain damage in the developing fetus, during birth, or from illness just after birth. No two cases of CP are the same, and the term is used to describe a variety of conditions depending on which part of the brain was damaged. For example, some people with CP may have learning disabilities, speech problems, hearing impairment or epilepsy.

"Cerebral" refers to the brain and "palsy" to muscle weakness/poor control.

Cone

Cone is a receptor cell which is sensitive to light and is located in the retina of the eye. It is responsible for color vision.

Convergence

Convergence means the ability to use both eyes as a team and to be able to turn the eyes inward to maintain single vision up close.

Cornea

Cornea is the transparent, blood-free tissue covering the central front of the eye (over the pupil, iris, and aqueous humor) that initially refracts or bends light rays as light enters the eye. Contact lenses are fitted over the cornea. The diameter of the cornea of an adult is typically 11-12 mm.

Dwell time

Gaze dwell time is the total duration that a fixation remains within a specific area. Gaze dwell time can be used as an indirect indicator of mental workload by noting its effect on a number of different observed variables.

Electro-Oculography (EOG)

Relies on measurement of skin’s potential differences, using electrodes placed around the eye. A widely used method in the 1960’s. Measures eye movements relative to head position. Not generally suitable for Point of Regard (POR) measurement (unless head is also tracked).

Eye tracking

Eye tracking means figuring out the movement of eye as a person is looking at something. Video-based eye tracking devices observe a person's pupil to determine the direction of their gaze.

Eye-tracking can be used for input, by directly controlling a pointer on the screen, or even for communicating the gaze direction to a co-worker looking at the same document (much like a telepointer). Eye-tracking can also be used to study how user interfaces are being used and may give insight into screen layout issues and how users are performing their tasks.

Note: Eye Tracking can also refer to the ability of the eyes to smoothly and effortlessly follow a moving target (in vision research)

Eye-writing

Eye-writing (or eye-typing) means the process by which text is produced using eye control.

Fixation

Fixation occurs when we look (focus) at things, the ability to direct and maintain steady visual attention on a target. The eyes remain relatively still during fixations. Fixations typically last from 200 to 600 ms, depending on the task. Fixations happen between saccades.

Fixational eye movements

Fixation frequency

Fovea

Gaze awareness

Headmouse

Iris

Locked-in syndrome

Optokinetic eye movements

Point of Regard (POR)

Pupil diameter

Pursuit

<a name="saccades"></a> Saccade

Saccadic eye movements

Usability

User-centred design

Vergence eye movements

Vestibular eye movements

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