Under eye movements (synonyms: oculomotor , ocular motility ) is the total of all motor expressions and variations that the eyeballs ( eyeballs oculi are) available, conscious or unconscious, voluntary or involuntary rotate in different directions (or turn leave ) to. As an active event, they are the result of certain innervation processes and, in most variants, serve to absorb visual stimuli. In contrast to this, eye movements induced "outside" (for example by the so-called traction test ) are referred to as passive eye movements, the investigation of which is intended to provide information about, for example, mechanically caused motility disorders.
Human oculomotor functions are based on a very complex system with a number of control loops . In these control loops, certain functional requirements must be met. The retina, for example, acts as a kind of sensor, the central nervous system provides control mechanisms, and external eye muscles (six in humans) act as actuators. With the change in the eye position, there is also a change in the retina, and the flow of information becomes a circle.
The following classification of eye movements can be made:
- Ductions are the rotational movements of a single eye around a horizontal, vertical or oblique meridian
- Torsion is the rolling motion of one or both eyes around the sagittal axis
Versions (synonyms: eye turns, conjugated or associated eye movements , eye movements in the same direction )
- quick versions
- Saccades ( eye target movements, voluntary movements, spontaneous eye movements, command movements )
- rapid phases (of optokinetic and vestibular nystagmus )
- slow versions
- slow phases (of optokinetic nystagmus, subsequent movements , doll's head phenomenon in the vestibulo-ocular reflex )
- quick versions
Vergences (synonyms: disjugated eye movements , disjunctive eye movements , opposing eye movements )
- accommodative vergences
- fusional vergences
Depending on the type of eye movements, the retina “feels” different controlled variables. In the case of eye target movements, this is the position of the retinal image that is to be fixed foveolar . In optokinetic nystagmus, it is the speed at which the image moves across the retina. In the case of subsequent movements, it is a combination of the aforementioned control variables. In the case of vergences, it is the disparity and the sharpness of the image. All of these values are transmitted to the various controllers in the central nervous system, where a comparison is made with the actual values and the target values that depend on the attention paid. As a result, a corresponding command is sent to the eye muscles.
Eye movement physiology
The eyeball ( Bulbus oculi ) is an almost spherical body that can rotate around any number of axes within certain limits similar to a cardanic suspension , but does not change its position within the eye socket ( orbit ) or only changes it insignificantly. All possible axes of rotation intersect at a single point within the orbit, the so-called pivot point . In an emmetropic adult eye, this point is about 13.5 mm behind the vertex of the cornea , roughly on the line of the face. An eye movement is dependent on the direction of pull of a muscle force, which is determined by its muscle origin and muscle attachment (insertion) on the eyeball. If you connect the origin, attachment and pivot point, you get the so-called muscle level . The axis of rotation of a muscle is perpendicular to the plane of the muscle and passes through the pivot point. Every two eye muscles of an eye have a similar muscle level, have approximately the same axis of rotation, but differ in the direction of rotation . These muscles with the same axis of rotation but different directions of rotation are called antagonists .
The forces that only act on the circumference of the globe can be compared with the mechanical operating principle of a lever or roller . The point at which an eye muscle tangentially leaves the eyeball is called the tangential point . The circumference of the globe between the muscle insertion and the point of tangency is called the rolling path . The tangent point and pivot point of the eye result in the lever arm . The arrangement of the muscle attachment ensures that the force exerted acts tangentially on the eyeball and that the effective lever arm does not change.
If the eye does not move within the orbit, this does not mean that there is no force acting on the globe, but only that the torque applied in each direction is as great as the torque in the opposite direction. This equilibrium is a stable equilibrium and remains unchanged as long as the torques remain unchanged. If a lever or an acting force changes, the eye is moved - until a new equilibrium is reached. The difference between the applied torques determines the speed of the eye movement.
Basics of eye movement
Three axes of rotation are particularly noteworthy for eye movements: the z-axis , which runs vertically through the eye, the x-axis , which runs horizontally - both lie fronto-parallel in the plane of Listing (named after the German mathematician Johann Benedict Listing ) -, and the y-axis (also sagittal axis ), which forms the perpendicular to this plane at the pivot point. Eye movement terminology is based on the definition of these three axes.
The movements occur through reciprocal changes in the innervation. The law of Sherrington states that the innervation wears an antagonist to the extent in which the agonist is enhanced.
In addition, it makes it easier to understand the eye movements to look at the different viewing directions from a zero position. This neutral position is assumed with the head and body straight and looking straight ahead. It is called the primary position or primary position .
- Rotational movements of a single eye are called ductions . A distinction is made between adduction (movement towards the nose), abduction (movement towards the temple), supraduction or elevation (movement upwards) and infraduction or depression (movement downwards). A roll , i.e. a rotation around the y-axis, is called incycloduction if it takes place with the upper circumference of the cornea towards the nose, whereas it is called excycloduction if this movement is carried out towards the temple. In addition to their main functions, the six outer eye muscles fulfill other, more or less pronounced partial functions depending on the current direction of gaze.
- Simultaneous rotating movements of both eyes are divided into vergences and versions . Versions are conjugate (same-directional) eye movements, i.e. rotations around parallel axes with the same direction of rotation. One speaks of dextroversions when looking to the right, of levoversions when looking to the left and of supra- or infraversions when looking up or down. Dextrocycloversions are conjugate cyclic productions of both eyes in which the upper circumference of the cornea is tilted to the right. Their opposite movement is called a levocycloversion .
- Vergenzen refers to disjugated (opposing) eye movements, i.e. rotations around parallel axes with opposite directions of rotation. As a convergence eye movement is called, brings the facial lines from the parallel position out in front of the eyes of the overlap caused by a bilateral adduction. Accordingly, divergence is a bilateral abduction movement in which the lines of the face intersect behind the eyes. Furthermore, one speaks of a positive vertical divergence when the line of sight of the right eye deviates upwards from that of the left eye, and of a negative vertical divergence in the opposite case. An incyclovergence consists of an incyclic production on both sides, an excyclovergence of a bilateral exclusion.
- Our eyes constantly carry out the smallest movements, even if we subjectively have the impression that we are fixing a point completely calmly. These micro-movements can be divided into three forms:
- Slow micro-movements : These movements , also known as drifts , are carried out with an amplitude of approx. 2.5 arc minutes and a speed of 2–8 arc minutes / sec.
- Microsaccades : They have an amplitude between 3 and 50 arc minutes and a maximum speed of 8 ° / sec. up to 80 ° / sec., in each case as a linear function of the amplitude.
- Microtremor : It has an amplitude of less than 1 arc minute at a speed of up to 10 arc minutes / sec. and above.
Slow micro-movements and micro-saccades are used to control the fixation , in which, as a kind of corrective, they lead the lines of sight back again and again to the fixation object, from which they regularly deviate slowly to prevent local adaptation .
From the above-mentioned primary position, the eye can perform a purely horizontal movement around the z-axis or a vertical movement around the x-axis. These movements from the primary position to the left, right, up or down are called cardinal movements . After performing such a cardinal movement, the eye is in a so-called secondary position . If a vertical reduction and a horizontal reduction are carried out one after the other, the eye is in a so-called tertiary position . An eye also moves into this position when it moves around an inclined axis and not one after the other around the z-axis and the x-axis. This means that every conceivable line of sight of an eye represents the result of a movement around an axis from the primary position. The entirety of these axes forms a vertical, fronto-parallel plane at the pivot point of the eye, the so-called plane of Listing . The law of Listing states thus:
- All eye movements that lead from the primary position to a secondary or tertiary position are conceivable as ductions around axes that lie in one plane.
However, Listing's law does not apply to all eye movements. Cycle productions, i.e. rolling, take place around the y-axis, which is perpendicular to Listing's plane.
As anatomical position of rest is of Bielschowsky , refers to that position of the eyes, is unaffected dependent on any innervation, only by mechanical factors. However, since muscle innervation does not completely paralyze even during sleep, a simple measurement on living people is hardly possible. A distinction must be made between the anatomical rest position and the so-called relative rest position or fusion-free setting , which occurs after the fusion is interrupted .
Services of the musculoskeletal system
The excursion ability of the eye, i.e. the extent of the movements when certain eye muscles contract , is different in different viewing directions. Adduction and abduction are usually possible by approx. 50 °. A depression can be up to 60 °, an elevation rarely more than 45 °. The determination of the monocular excursion ability results in the monocular field of view of the right and left eye. In contrast, one speaks of the binocular field of vision in the area in which both eyes can fixate foveolarly. This differs again from the so-called fusion field of view, because in extreme viewing directions it is possible to fixate bifoveolarly, but a diplopia is triggered by uneven rolling, which is not fused in this situation.
Usually only a part of these maximum values is required in daily life. The field of view in use generally only uses excursions up to approx. 20 °, also supported by early head movements. The angular speed at which rapid eye movements ( saccades ) are performed is also dependent on their amplitude. It is a maximum of about 600 ° / sec. Follow-up movements show maximum speeds of approx. 100 ° / sec., Vergence movements rarely more than 20 ° / sec. This means that saccades are usually completed after approx. 50 msec, while fusion movements can last approx. 0.5–1 second. This type of eye movement normally requires a muscle strength of about 0.1-0.5 N , with the muscle insertions already under a tension of 0.05-0.1 N in the primary position. Experimental muscle strength measurements have shown that the strength of an eye muscle can increase up to 1 N without any subjective symptoms or signs of fatigue occurring. Nevertheless, this does not generally rule out a complete freedom from symptoms. So-called asthenopia can occur under certain circumstances or appropriate dispositions .
|Classification according to ICD-10|
|H51.-||Other eye movement disorders|
|ICD-10 online (WHO version 2019)|
There are a variety of eye movement and position disorders. These include all types of congenital or acquired strabismus , eye tremors ( nystagmus ) as well as mechanical and neurogenic disorders (for example orbital floor fracture , superior oblique myokymia , internuclear ophthalmoplegia , endocrine orbitopathy , supranuclear paralysis, etc.).
Topodiagnostics of eye movement disorders
In the clinical assessment of motility disorders and their localization, these can usually be assigned to one of the following four areas:
- Orbita (eye muscles)
- Subarachnoid space and cavernous sinus ( cranial nerves III, IV and VI)
- posterior fossa ( brain stem with cerebellum )
- supratentorial space (cerebral hemispheres)
In principle, when assigning movement disorders to one of these areas, one can rely on two criteria:
- are both eyes affected or just one?
- are all types of eye movements impaired or only parts of them?
To check all criteria, all types of movement must be systematically examined.
- maximum excursion ability (monocular field of view)
- Position of the eyes to one another (squint angles in different viewing directions)
- Speed and accuracy of eye target movements
- Stability of eye positions (to rule out spontaneous or directional nystagmus)
- optokinetic nystagmus and follow-up movements
- vestibulo-ocular reflex
The following rules can apply to assessment:
- If both eyes are affected, this indicates a disease of the eye muscles or the brain stem
- If all types of eye movements are impaired, the problem is probably in the eye muscles or the peripheral nerves
- If only parts of the eye movements are disturbed, one can assume that there is a functional failure in the central nervous system
- If only one eye is affected, this suggests a lesion of the cranial nerves III, IV or VI in the area between the brain stem and the orbit or possible mechanical restrictions in the orbit itself
- An isolated failure of the optokinetic nystagmus without further oculomotor disturbances indicates a hemispherical lesion, together with other motility disturbances or a gaze direction nystagmus indicates a defect of the brain stem or the cerebellum.
The direction of view is recognized by the white in the eye ( sclera ). In humans, the sclera is about three times larger than the more than 200 species of non-human primates, which means that the direction of the gaze can be clearly seen.
Fixations and saccades make up most of the conscious eye movements. During a fixation, the eye receives information from the environment via the retina and, after preprocessing, forwards it to the brain. During a saccade, on the other hand, the eye does not perceive any visual information. In this phase one is actually blind and sees it as one of the contributory causes of inattentiveness blindness , i.e. the unresponsiveness to visual stimuli due to a lack of attention. However, it has been experimentally confirmed that the processing of the data last received is indeed continued during this perception failure.
Eye movements are very individual and can be very different even in the same person under different conditions. The duration of the fixations and the pattern and lengths of the saccades are not only dependent on general characteristics such as gender and age, but also depend heavily on the habits, skills, interests and intentions of the viewer. Biological factors such as drug or caffeine consumption can also have a strong influence on eye movements. The most important property for research, however, is the strong change in eye movements due to the visual stimuli presented, for example the difficulty of a text or the complexity of an image. Only this dependency suggests the eye-mind hypothesis , namely that seeing and the cognitive processing of what is seen influence each other and allow conclusions to be drawn experimentally about each other. The process of seeing itself is therefore now also referred to as intentional seeing , i.e. an active, consciously controlled action by the viewer.
Research areas of eye movement research
Eye movement research examines the connections between gaze target and follow-up movements and processing processes in the brain and, as part of psychology, not only combines perception , cognitive and advertising psychology , but also supports disciplines such as linguistics , security technology or research into user-friendliness . By means of eye movement registration , eng. eye tracking , the machine measurement and recording of eye movements, data is first obtained, which is then scientifically evaluated by eye movement analysis.
To give an overview of the importance and capabilities of eye movement research, some current research areas are presented here. However, there are numerous other questions that eye movement research deals with. In general, however, eye movement analysis is used to falsify theories or to find the more likely between two competing models.
Due to its special construction, the eye does not take a photographic image of the surroundings, but simultaneously generates up to 100 blurred and extremely compressed overall images of the peripheral field of vision as well as 3 to 4 high-resolution points per second with the help of foveal perception. These data are compared with existing images and converted into a perception (as happens when reading texts, see reading ).
Due to the eye movement registration , the typical eye movements when reading are known today. In the western room the fast saccades run from left to right and top to bottom - they follow an imaginary diagonal that is predetermined by the direction of reading. In addition, there are also regressions (reading saccades) that are opposite to the reading direction and lead back to text passages that have already been read. These regressions are often specifically provoked and examined, because they provide information about how sentences are analyzed in their structure and their meaning is determined.
Depending on the experience of the perceiver, the difficulty of the text and the context of the information intake, the measurable attributes vary in the following way: With increasing demand and decreasing predictability of the visual information, the saccades become shorter and the fixation phases longer. In the case of ambiguous and ambiguous text content, the proportion of regressions increases.
There are two competing models that attempt to explain how readers determine their eye movements. The cognitive process model claims that the gaze does not jump to the next word until a certain trigger condition has been met. This condition should be "lexical access", that is, the moment when a word is clearly identified. The meaning of the word and its position in the text do not have to be clear at this point. The oculomotor model, on the other hand, says that eye movements are mainly controlled by simple rules that are given to the eye. For example, a reader first determines a text-wide strategy based on his intention (for example, “read as carefully as possible”) and then works his way through a sentence with the help of an adapted tactic (for example “sentence is complicated, do it slowly”). The research results seem to agree with the cognitive process model rather than the oculomotor model , but none of the numerous modifications of these basic models have so far been clearly confirmed.
As a speed reader is referred to people who read with 600 to 700 words per minute about twice to three times as fast as the average reader while covering a major part of the text. Experimental studies show that an average reader who is instructed to “skim through” a text achieves a comparable speed and receptiveness.
Reading special fonts
Other objects of investigation are reading special scripts such as musical notation or mathematical formulas. In both areas, the eye movements are extremely dependent on the content of the information presented. Notations with many chords are characterized, for example, by numerous vertical eye movements, while pieces with contrapuntal melodies predominate in horizontal saccades.
Areas of application for eye movement analysis
The investigation of the way in which people look at real scenes or their images forms the basis for the practical application of eye movement research. The analysis of which points in a picture or photo are looked at first and which for the longest provides information for answering questions such as: "Which features have to be looked at in order to recognize a face?", "Where do I have to put up traffic signs with them they can be seen? "," How should the operating elements of a graphical user interface be designed? " , " Where are safety and warning notices on products, machines (e.g. risk of injury) or in buildings (e.g. emergency exit, escape route) place so that they can be picked up quickly? " , etc.
Practical findings from eye movement analysis are used to improve the functionality of interfaces and media information carriers . This includes, for example, the investigation of the legibility and perception of texts and images in advertising. In consumer research, the gaze behavior of advertising messages (e.g. advertisements, outdoor advertising, websites) has been investigated since the early 1970s, when appropriate biometric measuring devices were available. The aim is to assess the gaze behavior and the information intake. It is u. a. The question of which signals are recorded in picture elements, graphics or text, in which order and with what length of stay. It has been empirically proven that images of the same size are analyzed and decoded earlier by the viewer than texts (picture-before-text rule). The lingering on picture elements of images, the fixations , and the movements to the next picture element, the saccades , are interpreted in the eye movement analysis. Each course of the gaze is divided into a certain number of fixations and saccades, depending on the medium and the tendency of the viewer to deal with the medium. It has been empirically investigated that a fixation takes an average of 200 to 400 msec, while an average saccade takes 30 to 90 msec. While the fixations represent an intensive absorption of information and its cognitive processing, the saccades are rapid jumping movements of the eye in order to absorb new information. The conception of advertising material is examined in this way. This is based on the fact that the reading behavior of images and texts (except e.g. in the Arab world) runs from top to bottom and right to left ( read-write direction ). The aim is to support the absorption of information through optimally placed images / picture elements, headlines , running texts , brand signatures, etc. The conceptual arrangement of the image, text and graphic elements of an advertising medium then results in a "guided" gaze behavior (sequence of signal processing), which decides on the duration of viewing and the intensity of cognitive information processing.
In computer science, it can be used as a method of researching software ergonomics in the area of user-friendliness and then serves to analyze the quality of interfaces in human-computer interaction , such as graphic user interfaces .
Eye movements without perception
Rapid Eye Movements
In sleep research , rapid and violent eye movements are an indicator of what is known as REM sleep , a phase of sleep during which eye activity increases and the pupils tremble. This REM phase (abbreviation of R apid E ye M ovement ) is apparently correlated with the dream phases of sleep. If you wake up sleeping people during a REM phase, they can report dreams particularly often. In sleep laboratory tests, test subjects were able to send pre-arranged signals to the test director by means of certain eye movements during a lucid dream . This indicates that the dreamed eye movements are reproduced by the real eye muscles, that in contrast to other muscles, these are not "switched off" during sleep. However, the purpose of REM is unclear, since dreams can also be experienced in other phases of sleep and EMG recordings can also provide signals to other muscles.
A reflex movement of the eyes upwards and outwards during the eyelid closure and with the eyes closed is known as Bell's phenomenon. It is considered a protective mechanism.
In the EMDR ( E ye M ovement D esensitization and R eprocessing ) treatment method of psychotherapy , trauma is treated through the conscious use of eye movements. Similar to the model presented above, eye movements are seen here as being linked to access to various memory centers in the brain. The movements are intended to specifically address these centers and thus initiate a flow of information between the right and left hemispheres of the brain. With these eye movements, pure movement is in the foreground, there is no conscious perception. The therapy is controversial: EMDR is viewed by some clinical psychologists as a pseudoscience or as falsified.
- Michael Tomasello : Why we cooperate. Suhrkamp Verlag, Berlin 2010, ISBN 978-3-518-26036-4 , (Original title: Why We Cooperate)
- Herbert Kaufmann (Ed.) : Strabismus . 4th fundamentally revised and expanded edition, with Heimo Steffen, Georg Thieme Verlag, Stuttgart, New York 2012, ISBN 3-13-129724-7 .
- Keith Rayner : Eye movements in reading and information processing: 20 years of research. In: Psychological bulletin. Volume 124, Number 3, November 1998, pp. 372-422. PMID 9849112 (Review).
- Keith Rayner: Eye Movements and Visual Cognition Scene Perception and Reading . Springer, Heidelberg 1993, ISBN 3-540-97711-2 . (meanwhile no longer entirely up-to-date but comprehensive overview of the research area)
- K. Seifert, M. Rötting: Journal edition “Special Issue: Eye Movement”. 2003. ISSN 1439-7854
- PJA Unema: Eye Movements and Mental Effort . Shaker Verlag , 1995, ISBN 3-8265-0824-6 .
- H. Shimazu, Y. Shinoda (Eds.): Vestibular and Brain Stem Control of Eye, Head and Body Movements . Karger, 1992, ISBN 3-8055-5548-2 . (neuroscientific approach to the subject of eye movements)
- ↑ Michael Tomasello : Why we cooperate. Suhrkamp Verlag, Berlin 2010, ISBN 978-3-518-26036-4 , p. 65. (Original title: Why We Cooperate)
- ↑ Hans-Werner Hunziker: In the eye of the reader: foveal and peripheral perception - from spelling to reading pleasure . Transmedia, Stäubli Verlag, Zurich 2006, ISBN 3-7266-0068-X .
- ↑ Dr. med. Heike Schuhmacher Mistakes have to be seen!
- ↑ a b c d e f g h Werner Kroeber-Riel: Consumer behavior . 5th edition. Verlag Franz Wahlen, Munich 1992, ISBN 3-8006-1656-4 , p. 240 ff .
- ↑ JD Herbert, SO Lilienfeld, JM Lohr, RW Montgomery, WT O'Donohue, GM Rosen, DF Tolin: Science and pseudoscience in the development of eye movement desensitization and reprocessing: implications for clinical psychology . In: Clinical psychology review . tape 20 , no. 8 , November 2000, pp. 945-971 , PMID 11098395 .
- ^ Richard J. McNally: Is the pseudoscience concept useful for clinical psychology ?: The Demise of Pseudoscience . In: The Scientific Review of Mental Health Practice . tape 2 , no. 2 , 2003 ( online ).