eye tracking and pupillometry

cognitive neuroscience

what is the pupil?

the opening in front of our eye that allows light to pass through the lens

what is the cornea?

transparent extension of the sclera to the front of the eye that protects our eye

function of aqueous humor in anterior chamber?

supplies nutrients to the cornea and lens

function of posterior chamber?

produces the aqueous humor, which then flows through the pupil into the anterior chamber

function of ciliary muscle?

adjusts the refractive power of the lens

function of choroid?

rich capillary body that nourishes the retinal photoreceptors

what is the sclera?

outermost, opaque layer of the eye

what is the retina?

what is the fovea?

section of retina that has the highest visual acuity

what is the optic disk?

function of vitreous humor?

maintains eye shape and contains phagocytic cells that remove blood and other debris that might otherwise interfere with light transmission (its failure leads to floaters)

what is the lens?

what are zonule fibers?

connective tissue bands that hold the lens of the eye in place

function of iris?

contains muscles that adjust the size of the pupil

what is the foveola?

the centre of the fovea; contains only cone cells, more densely packed than anywhere else on the retina => maximal acuity

what is the visual axis?

a line passing from the centre of the visual field of the eye, through the centre of the lens, to the fovea

by what is the optic nerve protected?

the optic nerve is protected by meninges

what are the 6 extra ocular muscles?

lateral rectus and medial rectus (which control horizontal movement),

superior rectus and inferior rectus (which control vertical movement),

superior oblique and inferior oblique (which enable complex eye rotation).

what roles do the extra ocular muscles play?

what are the 5 types of eye movements?

smooth pursuit, saccades, vergence, vestibulo-ocular (reflex) and optokinetic (reflex)

what are the eye movements that are characterized by shift in eye position?

smooth pursuit, saccades, vergence

what are the eye movements that are characterized by stabilizing movements?

vestibulo-ocular (reflex) and optokinetic (reflex)

what is smooth pursuit?

a voluntary, slow tracking movements of the eyes, meant to maintain a moving target on the fovea, once foveation is achieved

what are saccades?

rapid (ballistic) eye movements

what is vergence?

simultaneous movement of both eyes in opposite away directions

what is the vestibulo-ocular (reflex)?

uses information from the vestibular labyrinth of the inner ear to generate eye movements that stabilize gaze during head movements

what is the optokinetic (reflex)?

allows the eyes to follow objects in motion when the head remains stationary (e.g., from a moving train)

what is fixation?

maintenance of gaze at a fixed location

what is peripheral vision?

large field of view, but: lower resolution, contrast sensitivity, higher positional uncertainty, and more crowding

what is foveal vision?

maximal acuity and contrast sensitivity in a small region around the gaze position

what is saccadic suppression (of image displacement)?

perceptually suppressing retinal image motion during eye movements

Louis Émile Javal (1879)?

Noticed that people made saccades and fixations while reading.

Edmund Burke Huey (1908)?

Built the first eye tracker (a lens placed on the cornea, with an opening for the pupil and a pointer attached to it); tracked eye movements during reading.

Guy Thomas Buswell (1937)?

Used light beams which were reflected on readers’ eyes and recorded them on film. He noticed that there is a significant difference between oral and silent reading.

Alfred Lukyanovich Yarbus (1967)?

Noticed that readers’ eye movement and fixation depend on their interest and the given task;

what do you use so eye trackers work?

near- infrared light

simply how do eye trackers work?

by directing near-infrared light towards the centre of our pupil and detecting the reflexion in both the pupil and the cornea (together or separately)

in eye tracking, the pupil only mode…?

the pupil only mode allows for higher sampling rates (i.e., how many times per second the eye tracker registers the position of the eye (in Hz))

in eye tracking, the pupil and corneal reflexion mode…?

the pupil plus corneal reflexion mode does a better job correcting for ocular drift (i.e., unconscious movements our eyes make when fixating on something)

what is Infrared Light (IR)?

the light found just past what is visible to the human eye

what is Near-Infrared Light (NIR)?

the section of electromagnetic radiation (EMR) wavelengths nearest to the visible range but just past what we can see

define wavelength

quantitative property of waves reflecting the distance between two consecutive peaks

define wave

oscillation which propagates in space, without carrying matter, but carrying energy with it when traveling

compare optical axis and visual axis

optical axis=imaginary line perpendicular to the cornea that intersects the center of the pupil (CP)

visual axis=imaginary line that connects an object in space, the center of the pupil, and the center of the fovea

what is one of the objectives of the calibration procedure?

to fine-tune the geometry to get as close as possible to the true location of the fovea

what does the eye tracker need to learn?

where the visual axis is

define root mean square (RMS) precision

the average difference between a measured value and the true value

define microsaccades

miniature fixational eye movements of ~6-25 ms in duration, that occur at a rate of about 1-2/s

what is one important fact about pupil dilation?

pupils do NOT dilate symmetrically or concentrically around their centre

what happens when the iris constrictor muscle contracts?

what happens when the iris dilator muscle contracts?

the iris constrictor muscle is controlled by?

the parasympathetic nervous system, the part of the autonomic nervous system that is involved in homeostasis (i.e., keeping the body in stable condition)

the iris dilator muscle is controlled by?

the sympathetic nervous system, the part of the autonomic nervous system that is involved in arousal, wakefulness, and the fight-or-flight response

what is anisocoria?

a condition characterized by an unequal size of the eyes' pupils

define dwell time

time spent investigating a particular area of interest (AOI) (i.e., visual attention)

who are the pioneers of psychophysics?

Ernst Heinrich Weber and Gustav Theodor Fechner

define psychophysics

scientific, quantitative study of the relationship between the physical properties of stimuli and the sensations and perceptions they elicit (it can be applied to any sensory system)

the term psychophysics was coined by…?

Gustav Theodor Fechner

who was inspired by the work of whom? (relating to psychophysics)

Gustav Theodor Fechner was inspired by the work of Ernst Heinrich Weber, who formulated the concept of “just noticeable difference”