Eye movement in language reading
Encyclopedia
Eye movement
in reading
involves visual processing
of words. This was first described by the French ophthalmologist
Louis Émile Javal
in the late 19th century. He reported that eyes do not move continuously along a line of text, but make short rapid movements (saccade
s) intermingled with short stops (fixations
). Javal's observations were characterised by a reliance on naked-eye observation of eye movement in the absence of technology. From the late 19th to the mid-20th century, investigators used early tracking technologies to assist their observation, in a research climate that emphasised the measurement of human behaviour
and skill for educational ends. Most basic knowledge about eye movement was obtained during this period. Since the mid-20th century, there have been three major changes: the development of non-invasive eye-movement tracking equipment; the introduction of computer technology to enhance the power of this equipment to pick up, record and process the huge volume of data that eye movement generates; and the emergence of cognitive psychology
as a theoretical and methodological framework within which reading processes are examined. Sereno & Rayner (2003) believed that the best current approach to discover immediate signs of word recognition is through the recordings of Eye movements and Event-related potential
.
Skilled readers move their eyes during reading on the average of every quarter of a second. During the time that the eye is fixated, new information is brought into the processing system. While the average fixation duration is 200–250 ms (thousandths of a second), the range is from 100 ms to over 500 ms. The distance the eye moves in each saccade (or short rapid movement) is between 1 and 20 characters with the average being 7–9 characters. The saccade lasts for 20-40 ms and during this time vision is suppressed so that no new information is acquired. Thus, the most impressive fact about fixations (the point at which a saccade jumps to) and saccades is that there is considerable variability not only between readers, but for the same person reading a single passage of text. Additionally, skilled readers make regressions back to material already read about 15 percent of the time. The main difference between faster and slower readers is that the latter group consistently shows longer average fixation durations, shorter saccades, and more regressions. These basic facts about eye movement have been known for almost a hundred years, but only recently have researchers begun to look at eye movement behavior as a reflection of cognitive processing during reading.
On one hand, if the perceptual span includes all or many of the words on a line of text, then eye movement measures would not likely reveal much information about cognitive processing; however, if the reader gains useful information only from the word directly focused on, then eye movement behavior could shed light on what role the eyes play in reading disorders such as dyslexia
.
This picture shows the acuity
of foveal vision in reading (during one eye stop).
The lower line of text simulates the acuity of vision with the relative acuity percentages
To do a test, close one eye, fixate the upper line at the fixation point and try to read the words to the right and left without moving your eyes.
The result should be similar to the incrementally blurred lower line of text - except that you never have the impression of a blurred text. The reason: Your visual perception is already the result of a massive computational analysis made by your brain. Your system "knows" that the upper line is not blurred, so you do not see it as blurred. But the difficulty of recognition increases with the distance from the fixation point.
and naked-eye observation. For example, Ibn al Haytham, a medical man in 11th-century Egypt, is reported to have written of reading in terms of a series of quick movements and to have realised that readers use peripheral
as well as central vision
.
Leonardo DaVinci, (1452-1519) was the first in Europe to recognize the special optical qualities of the eye. He derived his insights partly through introspection but mainly through a process that could be described as optical modelling. Based on dissection of the human eye he made experiments with water-filled crystal balls. He wrote "The function of the human eye, ... was described by a large number of authors in a certain way. But I found it to be completely different."
His main experimental finding was that there is only a distinct and clear vision at the "line-of-sight", the optical line that ends at the fovea
. Although he did not use these words literally he actually is the father of the modern distinction between foveal vision (a more precise term for central vision) and peripheral vision
. However, Leonardo did not know that the retina is the sensible layer, he still believed that the lens is the organ of vision.
There appear to be no records of eye movement research until the early 19th century. At first, the chief concern was to describe the eye as a physiological and mechanical moving object, the most serious attempt being Hermann von Helmholtz
's major work Handbook of physiological optics (1866). The physiological approach was gradually superseded by interest in the psychological aspects of visual input, in eye movement as a functional component of visual tasks. As early as the 1840s, there was speculation on the relationship between central and peripheral vision.
The subsequent decades saw more elaborate attempts to interpret eye movement, including a claim that meaningful text requires fewer fixations to read than random strings of letters. In 1879, the French ophthalmologist
Louis Émile Javal
used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements for which he coined the term saccade
s. In 1898, Erdmann & Dodge used a hand-mirror to estimate average fixation duration and saccade length with surprising accuracy.
is a tool created to help measure eye and head movements. The first devices for tracking eye movement took two main forms: those that relied on a mechanical connection between participant and recording instrument, and those in which light or some other form of electromagnetic energy was directed at the participant's eyes and its reflection measured and recorded. In 1883, Lamare was the first to use a mechanical connection, by placing a blunt needle on the participant's upper eyelid. The needle picked up the sound produced by each saccade and transmitted it as a faint clicking to the experimenter's ear through an amplifying membrane
and a rubber tube. The rationale behind this device was that saccades are easier to perceive and register aurally than visually. In 1889, Edmund B. Delabarre
invented a system of recording eye movement directly onto a rotating drum by means of a stylus
with a direct mechanical connection to the cornea
. Other devices involving physical contact with the surface of the eyes were developed and used from the end of the 19th century until the late 1920s; these included such items as rubber balloons and eye caps.
Mechanical systems suffered three serious disadvantages: questionable accuracy due to slippage of the physical connection, the considerable discomfort caused to participants by the direct mechanical connection (and consequently great difficulty in persuading people to participate), and issues of ecological validity
, since participants' experience of reading in trials was significantly different from the normal reading experience. Despite these drawbacks, mechanical devices were used in eye movement research well into the 20th century.
Attempts were soon made to overcome these problems. One solution was to use electromagnetic energy rather than a mechanical connection. In the "Dodge technique", a beam of light was directed at the cornea, focused by a system of lenses and then recorded on a moveable photographic plate. Erdmann & Dodge used this technique to claim that there is little or no perception during saccades, a finding that was later confirmed by Utall & Smith using more sophisticated equipment. The photographic plate in the Dodge technique was soon replaced with a film camera, but was still plagued by problems of accuracy, due to the difficulty of keeping all parts of the equipment perfectly aligned throughout a trial and accurately compensating for the distortion caused by the diffractive qualities of photographic lenses. In addition, it was usually necessary to restrain a participant's head by using an uncomfortable bite-bar or head-clamp.
In 1922, Schott pioneered a further advance called electro-oculography (EOG), a method of recording the electrical potential between the cornea and the retina
. Electrodes may be covered with special contact paste before being placed on the skin. So, it is now unnecessary to make incisions in patient's skin. Common misconception about EOG is that measured potential is the electromyogram of extraocular muscles. In fact, it is only the projection of eye dipole to the skin, because higher frequencies, corresponding to EMG, are filtered out. EOG delivered considerable improvements in accuracy and reliability, which explain its continued use by experimentalists for many decades.
Eye movement
Eye movement may refer to:* Eye movement , the voluntary and involuntary movement of the eyes* Eye movement in reading, the role of eye movement in reading linguistic text* Eye movement in music reading, the role of eye movement in reading music...
in reading
Reading (process)
Reading is a complex cognitive process of decoding symbols for the intention of constructing or deriving meaning . It is a means of language acquisition, of communication, and of sharing information and ideas...
involves visual processing
Visual processing
Visual processing is the sequence of steps that information takes as it flows from visual sensors to cognitive processing. The sensors may be zoological eyes or they may be cameras or sensor arrays that sense various portions of the electromagnetic spectrum....
of words. This was first described by the French ophthalmologist
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
Louis Émile Javal
Louis Émile Javal
Louis Émile Javal was a French ophthalmologist born in Paris. Originally trained as a civil engineer, he switched to the medical profession, receiving his degree from the University of Paris in 1868. Following graduation he travelled to Berlin and studied under Albrecht von Graefe...
in the late 19th century. He reported that eyes do not move continuously along a line of text, but make short rapid movements (saccade
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
s) intermingled with short stops (fixations
Fixation (visual)
Fixation or visual fixation is the maintaining of the visual gaze on a single location. Humans typically alternate saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appear to have developed for hunting prey...
). Javal's observations were characterised by a reliance on naked-eye observation of eye movement in the absence of technology. From the late 19th to the mid-20th century, investigators used early tracking technologies to assist their observation, in a research climate that emphasised the measurement of human behaviour
Human Behaviour
"Human Behaviour" is Icelandic singer Björk's first solo single, taken from the album Debut. It contains a sample of "Go Down Dying" by Antonio Carlos Jobim. The lyrics reflect on human nature and emotion from a non-human animal's point of view. The song is the first part of a series of songs that...
and skill for educational ends. Most basic knowledge about eye movement was obtained during this period. Since the mid-20th century, there have been three major changes: the development of non-invasive eye-movement tracking equipment; the introduction of computer technology to enhance the power of this equipment to pick up, record and process the huge volume of data that eye movement generates; and the emergence of cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....
as a theoretical and methodological framework within which reading processes are examined. Sereno & Rayner (2003) believed that the best current approach to discover immediate signs of word recognition is through the recordings of Eye movements and Event-related potential
Event-related potential
An event-related potential is any measured brain response that is directly the result of a thought or perception. More formally, it is any stereotyped electrophysiological response to an internal or external stimulus....
.
Eye movement in reading
On one hand, if the perceptual span includes all or many of the words on a line of text, then eye movement measures would not likely reveal much information about cognitive processing; however, if the reader gains useful information only from the word directly focused on, then eye movement behavior could shed light on what role the eyes play in reading disorders such as dyslexia
Dyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
.
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
of foveal vision in reading (during one eye stop).
The lower line of text simulates the acuity of vision with the relative acuity percentages
To do a test, close one eye, fixate the upper line at the fixation point and try to read the words to the right and left without moving your eyes.
The result should be similar to the incrementally blurred lower line of text - except that you never have the impression of a blurred text. The reason: Your visual perception is already the result of a massive computational analysis made by your brain. Your system "knows" that the upper line is not blurred, so you do not see it as blurred. But the difficulty of recognition increases with the distance from the fixation point.
Unassisted observation, optical modelling and psychological introspection
Until the second half of the 19th century, researchers had at their disposal three methods of investigating eye movement. The first, unaided observation, yielded only small amounts of data that would be considered unreliable by today's scientific standards. This lack of reliability arises from the fact that eye movement occurs frequently, rapidly, and over small angles, to the extent that it is impossible for an experimenter to perceive and record the data fully and accurately without technological assistance. The other method was self-observation, now considered to be of doubtful status in a scientific context. Despite this, some knowledge appears to have been produced from introspectionIntrospection
Introspection is the self-observation and reporting of conscious inner thoughts, desires and sensations. It is a conscious and purposive process relying on thinking, reasoning, and examining one's own thoughts, feelings, and, in more spiritual cases, one's soul...
and naked-eye observation. For example, Ibn al Haytham, a medical man in 11th-century Egypt, is reported to have written of reading in terms of a series of quick movements and to have realised that readers use peripheral
Peripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
as well as central vision
Fovea
The fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
.
His main experimental finding was that there is only a distinct and clear vision at the "line-of-sight", the optical line that ends at the fovea
Fovea
The fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
. Although he did not use these words literally he actually is the father of the modern distinction between foveal vision (a more precise term for central vision) and peripheral vision
Peripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
. However, Leonardo did not know that the retina is the sensible layer, he still believed that the lens is the organ of vision.
There appear to be no records of eye movement research until the early 19th century. At first, the chief concern was to describe the eye as a physiological and mechanical moving object, the most serious attempt being Hermann von Helmholtz
Hermann von Helmholtz
Hermann Ludwig Ferdinand von Helmholtz was a German physician and physicist who made significant contributions to several widely varied areas of modern science...
's major work Handbook of physiological optics (1866). The physiological approach was gradually superseded by interest in the psychological aspects of visual input, in eye movement as a functional component of visual tasks. As early as the 1840s, there was speculation on the relationship between central and peripheral vision.
The subsequent decades saw more elaborate attempts to interpret eye movement, including a claim that meaningful text requires fewer fixations to read than random strings of letters. In 1879, the French ophthalmologist
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
Louis Émile Javal
Louis Émile Javal
Louis Émile Javal was a French ophthalmologist born in Paris. Originally trained as a civil engineer, he switched to the medical profession, receiving his degree from the University of Paris in 1868. Following graduation he travelled to Berlin and studied under Albrecht von Graefe...
used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements for which he coined the term saccade
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
s. In 1898, Erdmann & Dodge used a hand-mirror to estimate average fixation duration and saccade length with surprising accuracy.
Early tracking technology
Eye tracking deviceEye Tracking Device
The Eye Tracking Device is a headmounted device, designed for measurement ofthree-dimensional eye and head movements under experimental and natural conditions.The tracker permits comprehensive measurement of eye movement...
is a tool created to help measure eye and head movements. The first devices for tracking eye movement took two main forms: those that relied on a mechanical connection between participant and recording instrument, and those in which light or some other form of electromagnetic energy was directed at the participant's eyes and its reflection measured and recorded. In 1883, Lamare was the first to use a mechanical connection, by placing a blunt needle on the participant's upper eyelid. The needle picked up the sound produced by each saccade and transmitted it as a faint clicking to the experimenter's ear through an amplifying membrane
Membrane (selective barrier)
A membrane is a layer of material which serves as a selective barrier between two phases and remains impermeable to specific particles, molecules, or substances when exposed to the action of a driving force...
and a rubber tube. The rationale behind this device was that saccades are easier to perceive and register aurally than visually. In 1889, Edmund B. Delabarre
Edmund B. Delabarre
Edmund Burke Delabarre , was a researcher and professor of psychology at Brown University. He graduated from Amherst College in 1886. Professor Delabarre was a pioneer in the field of shape perception and on the interaction between mental processes and the involuntary movements of the body...
invented a system of recording eye movement directly onto a rotating drum by means of a stylus
Stylus
A stylus is a writing utensil, or a small tool for some other form of marking or shaping, for example in pottery. The word is also used for a computer accessory . It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styli are heavily curved to be held more easily...
with a direct mechanical connection to the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
. Other devices involving physical contact with the surface of the eyes were developed and used from the end of the 19th century until the late 1920s; these included such items as rubber balloons and eye caps.
Mechanical systems suffered three serious disadvantages: questionable accuracy due to slippage of the physical connection, the considerable discomfort caused to participants by the direct mechanical connection (and consequently great difficulty in persuading people to participate), and issues of ecological validity
Ecological validity
Ecological validity is a form of validity in a research study. For a research study to possess ecological validity, the methods, materials and setting of the study must approximate the real-life situation that is under investigation. Unlike internal and external validity, ecological validity is not...
, since participants' experience of reading in trials was significantly different from the normal reading experience. Despite these drawbacks, mechanical devices were used in eye movement research well into the 20th century.
Attempts were soon made to overcome these problems. One solution was to use electromagnetic energy rather than a mechanical connection. In the "Dodge technique", a beam of light was directed at the cornea, focused by a system of lenses and then recorded on a moveable photographic plate. Erdmann & Dodge used this technique to claim that there is little or no perception during saccades, a finding that was later confirmed by Utall & Smith using more sophisticated equipment. The photographic plate in the Dodge technique was soon replaced with a film camera, but was still plagued by problems of accuracy, due to the difficulty of keeping all parts of the equipment perfectly aligned throughout a trial and accurately compensating for the distortion caused by the diffractive qualities of photographic lenses. In addition, it was usually necessary to restrain a participant's head by using an uncomfortable bite-bar or head-clamp.
In 1922, Schott pioneered a further advance called electro-oculography (EOG), a method of recording the electrical potential between the cornea and the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. Electrodes may be covered with special contact paste before being placed on the skin. So, it is now unnecessary to make incisions in patient's skin. Common misconception about EOG is that measured potential is the electromyogram of extraocular muscles. In fact, it is only the projection of eye dipole to the skin, because higher frequencies, corresponding to EMG, are filtered out. EOG delivered considerable improvements in accuracy and reliability, which explain its continued use by experimentalists for many decades.
Cognitive psychology, infrared tracking and computer technology
Eye trackers bounce near infra-red light off the interior of the eyeball, and monitor the reflection on the eye to determine gaze location. With this technique, the exact position of fixation on screen is determinable. Wang (2011) mentioned that a video-based eye-tracker which uses video cameras to record the eye position of human subjects, thereby recording pupil dilation and eye movements, can be use to examine how fixations, saccades, and pupil dilation responses are related to the information on the screen and behavioral choices during an experiment. According to Wang (2011:185), "understanding the relationship between these observables can help us to understand how human behavior in the economy can be affected by what information people acquire, where their attention is focused, what emotional state they are in, and even what brain activity they are engaged in. This is because fixations and saccades (matched with information shown on screen) indicate how people acquire information (and what they see), time lengths of fixations indicate attention, and pupil dilation responses indicate emotion, arousal, stress, pain, or cognitive load."See also
- Eye movement (sensory)
- Eye movement in music readingEye movement in music readingEye movement in music reading is the scanning of a musical score by a musician's eyes. This usually occurs as the music is read during performance, although musicians sometimes scan music silently to study it, and sometimes perform from memory without score. The phenomenon has been studied by...
- Gaze-contingency paradigmGaze-contingency paradigmThe gaze-contingency paradigm is a general term for techniques allowing to change the display on a computer screen in function of where the viewer is looking.Gaze-contingent techniques are part of the eye movement field of study in psychology...
- ReadingReading (process)Reading is a complex cognitive process of decoding symbols for the intention of constructing or deriving meaning . It is a means of language acquisition, of communication, and of sharing information and ideas...
- Fixation (visual)Fixation (visual)Fixation or visual fixation is the maintaining of the visual gaze on a single location. Humans typically alternate saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appear to have developed for hunting prey...
- Eye trackingEye trackingEye tracking is the 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 in research on the visual system, in psychology, in cognitive linguistics and in product...
- Eye tracking deviceEye Tracking DeviceThe Eye Tracking Device is a headmounted device, designed for measurement ofthree-dimensional eye and head movements under experimental and natural conditions.The tracker permits comprehensive measurement of eye movement...