Eye movement (sensory)

Under eye movements (synonyms: oculomotor, ocular motility ) is defined as the totality of all motor expressions and variations, the eyeballs ( eyeballs oculi ) are available, consciously or unconsciously, voluntarily or involuntarily rotate in different directions (or rotate ) can. You are an active event, the result of certain Innervationsvorgänge and serve in most variants of the acquisition of visual stimuli. In contrast, refers to "outside " induced eye movements ( for example, by the so-called traction test) as passive eye movements, whose investigation will provide information on, for example, mechanically induced motility disorders.

The oculomotor system of man takes place on the basis of a very complex system with a number of control loops. In these control loops certain functional requirements must be met. To the retina ( retinal ) serves as a kind of sensor, the central nervous system provides control mechanisms available, and six outer muscles of the eye ( in humans) function as an actuator. With the change of eye position also goes back a change on the retina associated, and the flow of information to the circle.

• 3.1 topodiagnosis of eye movement disorders

• 5.1 integration
• 5.2 Reading Text 5.2.1 Explanatory models
• 5.2.2 Speed ​​Reading

• 7.1 Rapid Eye Movements
• 7.2 Bell'sches phenomenon

Classification

The following classification of eye movements can be made:

• Reductions is called the rotational movements of one eye by a horizontal, vertical or oblique meridian
• Twist is called the rolling movements of one or both eyes around the sagittal axis
• Versions (synonyms: View twists, conjugated or associated eye movements, eye movements in the same direction ) fast versions Saccades ( eye target movements, voluntary movements, spontaneous eye movements, command movements )
• Rapid phases ( the optokinetic and vestibular nystagmus)

• Slow phases ( of optokinetic nystagmus, pursuit movements, doll's head phenomenon in the vestibulo-ocular reflex)

• Vergences (synonyms: disjugierte eye movements, disjunctive eye movements, reverse eye movements ) accommodative vergences
• Fusional vergences

Depending upon the type of eye movement "feels" the retina different control variables. In view target movements this is the position of the retinal image that is to be fixed foveolar. The optokinetic nystagmus, it is the speed of the image shift on the retina. For subsequent movements, it is a combination of the aforementioned control variables. In vergences it is the disparity and the sharpness of the image. All these values ​​are transmitted to the various regulators in the central nervous system, where a comparison with the actual values ​​and the dependent of the allocation of attention target values ​​is carried out. As a result, a corresponding control command is sent to the eye muscles.

Physiology of the eye movements

Movement mechanics

The eyeball ( eyeball ) is an almost spherical body, which may be similar to turning a gimbal to any number of axes within certain limits, compromising his position within the eye socket (orbit ) but not or only marginally changed. All possible rotational axes intersect at a single point in this case within the orbit, the so-called pivot. In an emmetropic eye this point is about 13.5 mm behind the corneal vertex, about on the line of sight. An eye movement depends on the pulling direction of muscle strength, which is determined by its muscle origins and muscle attachment ( insertion) to the eyeball. Connects to origin, insertion and rotation, one obtains the so-called muscle level. The axis of rotation of a muscle is the perpendicular to the muscle level, and performs the rotation. Two ocular muscles of the eye have a similar level of muscle, have approximately the same axis of rotation, but are distinguished by the direction of rotation. These muscles with the same axis of rotation, but different directions of rotation are called antagonists.

The forces acting exclusively on the circumference of the globe, can be compared with the mechanical action principle of lever or roller. The point at which an eye muscle leaves the eye ball tangentially, is called tangent point. The scope of the eyeball between muscle insertion and the point of tangency is called the rolling zone. Tangent point and rotation of the eye result in the lever arm. In this case, the arrangement of the muscle approach ensures that the force applied tangentially act on the eyeball and the effective lever arm does not change.

If the eye does not move within the orbit, this does not mean that no force acts on the globe, but only that the torque acting is so great in every direction as the torque in the opposite direction. This equilibrium is a stable equilibrium and remains unchanged for as long as the torques remain unchanged. If going a lever or an applied force, the eye is moved - and until a new equilibrium is reached. The difference between the torques acting in this case determines the speed of the eye movement.

Fundamentals of eye movement

Three axes of rotation are at eye movements highlighted: the z- axis that runs vertically through the eye, the x -axis, which runs horizontally - are both frontoparallel in the plane of Listing (named after the German mathematician Johann Benedict Listing) -, and the y-axis (also sagittal axis ) forming the perpendicular to this plane in the center of rotation. The terminology of the eye movement based on the definition of the three axes.

The motion carried by reciprocal modification of innervation. Sherrington 's law states that the innervation of an antagonist decreases to the extent in which the agonist is enhanced.

In addition, it facilitates the understanding of eye movements to look at the different viewing directions from a zero setting out. This zero position is adopted in straight head and body posture and straight directional views. It is called the primary position or primary position.

Movement types

• Rotational movements of a single eye is called productions. A distinction adduction ( movement toward the nose ), abduction ( movement to the temple ), Supraduktion or elevation ( upward movement ) and Infraduktion or depression ( downward movement ). A flanged connection, ie a rotation about the y- axis is called Inzykloduktion if it is done with the upper periphery of the cornea towards the nose, on the other hand Exzykloduktion if this movement is completed to the temple down. The six extraocular muscles meet here in addition to their main functions depending on the current view direction further, more or less distinct sub-functions.

• Anatomical representation of the muscle investments during the respective rotational movement from the primary position out

Adduction

Reduction

Innenrollung

Außenrollung

• Simultaneous rotational movements of both eyes are divided into vergences and versions. Versions are conjugated ( same direction ) eye movements, ie rotations about parallel axes in the same direction. One speaks of Dextroversionen in turn look to the right of Lävoversionen when looking to the left and of supra- and infra versions when looking up or down. Dextrozykloversionen are conjugated Zykloduktionen of both eyes, wherein the upper periphery of the cornea is tilted to the right. Their opposite movement called Lävozykloversion.
• With vergences is called disjugierte ( in opposite directions ) eye movements, ie rotations about parallel axes in the opposite direction. As convergence eye movement is called that brings out the parallel position out facial lines before the eyes of the overlap caused by a bilateral adduction. Accordingly, the divergence movement of bilateral abduction, in which the facial lines intersect behind the eyes. Furthermore it is called a vertical divergence positive when the line of sight of the right eye to the left eye is deviated upwardly from a negative vertical divergence in the opposite case. A Inzyklovergenz consists of a two-sided Inzykloduktion, a Exzyklovergenz from a two-sided Exzykloduktion.
• Our eyes run constantly from the slightest movements, even if we subjectively have the impression to fix a point perfectly calm. These micro-movements can be categorized into three types: Slow micromovements This also drifts mentioned movements are carried out with an amplitude of about 2.5 minutes of arc at a speed of 2-8 angular minutes / sec.
• Microsaccades: You have an amplitude between 3 and 50 arcmin, and a maximum speed of 8 ° / sec to 80 ° / sec, each a linear function of the amplitude.
• Micro tremor: He has an amplitude of less than 1 arc minute at a speed of up to 10 minutes of arc / sec. and above.

Slow micro movements and microsaccades serve the fixation control in which they view the lines always lead back as a kind of corrective to the fixation object, they differ from regular slow for the purposes of prevention of local adaptation.

Eye positions

The eye can perform a pure horizontal movement around the z- axis or a vertical movement around the x- axis from the above primary position out. These movements from the primary heading out to the left, right, up or down is called cardinal movements. Having made such an cardinal movement the eye is in a so-called secondary position. Become a succession Vertikalduktion and a Horizontalduktion performed, the eye is in a so-called tertiary position. In this position an eye passes, even if it performs a movement about an oblique axis and not in succession about the z -axis and the x-axis. This means that every conceivable line of sight of an eye illustrating the result of movement about an axis from the primary position out. All of these axes forming the pivot point of the eye, a vertical frontoparallele plane, called plane of the listing. The law of Listing states thus:

• All eye movements, which lead out from the primary position in a secondary or tertiary position, are conceivable as productions about axes which lie in a plane.

However, the law of listing is not applicable to all eye movements. Zykloduktionen, that flicks, takes place around the y- axis, perpendicular to Listing's plane.

As anatomical position of rest of Bielschowsky that position of the eyes is called, which is unaffected dependent on any innervation, limited only by mechanical factors. As, however, not completely paralyzed a muscle innervation in his sleep, a simple measurement of living is hardly possible. From the anatomical position of rest, the so-called relative rest or fusion -free setting must be distinguished, which is present after interruption of the merger.

Performance of the musculoskeletal system

Excursion capacity of the eye, so the extent of the contraction movements of certain muscles of the eye, is different in different directions of view. Adduction and abduction is possible generally by about 50 °. Depression may be up to 60 °, an elevation rarely more than 45 °. The determination of monocular excursion capability yields the monocular visual field of the respective left and right eye. In contrast, one speaks of the binocular visual field in the area where both eyes can fix together foveolar. This differs again from the so-called fusion of sight, as in extreme directions of gaze, although can be fixed bifoveolar, but by page unequal roll of a diplopia is triggered, which is not fused in this situation.

Typically, only a portion of these maximum values ​​is needed in everyday life. The use of sight generally uses only excursions up to 20 °, also supported by early onset head movements. The angular velocity, are performed with the rapid eye movements ( saccades ), is also dependent on their amplitude. Maximum, it is about 600 ° / sec Pursuit movements show maximum speeds of about 100 ° / sec, Vergenzbewegungen rarely more than 20 ° / sec It follows that saccades are usually completed within 50 milliseconds, while fusion movements can take about 0.5 to 1 second. This form of eye movements normally requires a muscle force of about 0.1-0.5 N, where the muscle insertions in primary position are already under a voltage of 0.05-0.1 N. Experimental muscle force measurements have shown that the force of an eye muscle to up to 1 N can rise without subjective complaints or fatigue would have occurred. However, this includes a complete freedom from symptoms from not generally. Under certain circumstances, or appropriate dispositions may lead to so-called asthenopia.

Disturbances of the oculomotor

There are a number of disorders of eye movements and position. This includes all types of congenital or acquired strabismus, nystagmus ( nystagmus) as well as mechanical and neurogenic disorders (for example, orbital floor, superior oblique myokymia, internuclear ophthalmoplegia, endocrine ophthalmopathy, supranuclear gaze palsy, etc.).

Topodiagnosis of eye movement disorders

In the clinical evaluation of motility disorders and their localization, these can be assigned to one of the four following areas tend to be:

• Orbit ( eye muscles )
• Subarachnoid space and the cavernous sinus ( cranial nerve III, IV and VI)
• Posterior fossa ( brain stem with cerebellum )
• Supratentorial compartment ( cerebral hemispheres )

Principle, one can rely on one of these areas on two criteria, for assigning of movement disorders:

To test all criteria, all movement types must be systematically investigated.

• Maximum excursion capability ( monocular vision )
• Position of the eyes to each other ( squint angle in different directions of view )
• Speed ​​and accuracy of eye target movements
• Stability of eye positions (for the avoidance of spontaneous or gaze-evoked nystagmus )
• Optokinetic nystagmus and pursuit movements
• Vestibulo- ocular reflex

In order to assess the following rules may apply:

• If both eyes are affected, this indicates a disease of the eye muscles or the brain stem
• Are all species affected by eye movements, the fault is probably in the area of the eye muscles or peripheral nerves
• If only parts of the eye movements is disturbed, so one can start from a loss of function in the central nervous system
• If only one eye affected, this suggests a lesion of the cranial nerves III, IV or VI in the area between the brain stem and the orbit or for possible mechanical limitations in the orbit itself
• An isolated failure of the optokinetic nystagmus without further oculomotor disturbances suggests a Hemisphärenläsion, along with other motility disorders or nystagmus to a defect of the brainstem or the cerebellum.

Perception characteristics

The viewing direction is detected by the white in the eye ( sclera ). The sclera is in humans, in comparison to the more than 200 species of non-human primates, about three times larger, so that the viewing direction is much easier to recognize.

Fixations and saccades make up the largest part of the conscious eye movements. During a fixation, the eye takes over the retina on information from the environment and passes this on to a pre-processing to the brain. During a saccade, however, the eye receives no visual information. It is actually at this stage blind and sees it as one of the contributory causes of Unaufmerksamkeitsblindheit, so the unresponsiveness to visual stimuli through lack of attention. However, it was experimentally confirmed that while this perception failure, the processing of the data received last is very well continue.

Eye movements are very individual and can vary considerably under different conditions, even in the same person. The duration of the fixations, and the pattern and the lengths of saccades are not only dependent on general characteristics such as gender and age, but also depend strongly of habits, skills, interests and intentions of the observer. Biological factors such as drugs or caffeine consumption can heavily influence the eye movements. However, the most important for the research feature is the strong change in eye movements due to the presented visual stimuli, for example, the difficulty of a text or the complexity of an image. It is this dependence suggests the Eye- Mind Hypothesis, namely that seeing and the cognitive processing of the seen influence each other and allow experimentally justifiable inferences each other. The process of seeing itself therefore is now known as Intentional seeing, so an active, consciously controlled action by the sighted.

Research of eye movement research

The eye movement research examines the relationships between eye target and pursuit movements and treatment processes in the brain and connects as part of psychology not only perceptual, cognitive and advertising psychology, but also supports disciplines such as linguistics, the security technology or research into usability. Here, by means of eye tracking, Eng. eye tracking, the machine measure and record the eye movements, first obtained data, which are then scientifically evaluated by the eye movement analysis.

To give an overview of the importance and potential of eye movement research, here are representative presented some current research areas. However, there are numerous other issues with which the eye-tracking research employs. In general, the eye movement analysis is, however, used to falsify theories or to find out the more likely between two competing models.

Integration

Due to its special design, the eye does not take a photographic image of the area, but simultaneously generated per second up to 100 blurred and extremely compressed Total pictures in the peripheral visual field and 3-4 high-resolution points with the help of the foveal perception. These data are compared with existing mental images and transformed into a perception ( as in the reading of texts is done, see Reading ).

Reading Text

Through the eye tracking the typical eye movements during reading are known today. In the western area in this case run the fast saccades from right to left and top to bottom - so they follow an imaginary diagonal, which is determined by the direction of reading. In addition, however, it also comes to regressions, saccades, which are opposite to the direction of reading and lead back to already read passages. These regressions are often deliberately provoked and tested, because they provide information about how sentences analyzed in their structure and their semantic content is determined.

Depending on the experience of the perceiver, difficulty of the text and the context of the information recording vary the measurable attributes in the following manner: With increasing demand and declining predictability of visual information, the saccades are shorter and the longer fixation periods. Ambiguous and misleading text content, the proportion of regressions increases.

Explanatory models

There are two competing models that try to explain how readers set their eye movements. The cognitive process model asserts that looking only then jump to the next word when a certain trigger condition is met. This condition should be the " lexical access ", that is the moment in which a word is uniquely identified. The meaning of the word and its classification in the text would have at this time not yet be clear. The oculomotor model, however, states that the eye movements are mainly controlled by simple rules that would set the eye. To determine a reader because of its intention at first a text- wide strategy ( for example, " read carefully as possible " ) and work within a set using a customized tactics ( for example, " set is complicated, slow make ") in front. The research findings seem the cognitive process model rather than to give the right oculomotor model, however, has so far none of the numerous variations of these basic models are clearly confirmed.

Speed Reading

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 the average reader, who is instructed to " fly over " a text that reaches a similar speed and capacity.

Reading of special fonts

Further investigation objects are the reading of special fonts such as music notation or mathematical formulas. In both zones, the eye movements depend very strongly on the content of the information presented. Sheet sets with many chords are characterized for example by numerous vertical eye movements, while outweigh pieces with contrapuntal melody horizontal saccades.

Applications of eye-tracking analysis

The study of the manner in which such persons or their pictures look real scenes, forms the basis for the practical application of eye movement research. The analysis, which points in an image or photo first and which are considered the longest, gives instructions for answering questions like, " What characteristics must be considered in order to recognize a face ", " Where should I install traffic signs, thus they are seen? "," How should the controls of a graphical user interface be designed? " etc.

Practical insights of view motion analysis are used to improve interfaces and media in their function. This includes for example the study of clarity and visibility of text in advertising. In computer science, it can be used as an investigative method of software ergonomics for ease of use and then used to analyze the quality of interfaces for human-computer interaction, such as graphical user interfaces.

Eye movements without perception

Rapid Eye Movements

In sleep research fast and fierce eye movements are an indicator of the so-called REM sleep, a stage of sleep during which increases the eye activity and the pupils tremble. The function of REM ( short for Rapid Eye Movement) is unclear. Because the eyelids are usually closed when sleeping, no perception takes place. Wakes you people asleep during REM sleep, they may very often talk about dreams.

Bell'sches phenomenon

A reflex movement of the eyes upwards and outwards during the Lidschlusses and closed-eye is known as Bell'sches phenomenon. It is considered a protective mechanism.

Trauma Therapy

In the treatment method EMDR (Eye Movement Desensitization and Reprocessing ) trauma psychotherapy through the conscious use of eye movements to be treated. Similar to that model 's eye movements than with the access to various memory centers of the brain are considered connected here. The movements of these centers will be targeted specifically, such an information flow between the right and left brain are initiated. These eye movements, the only movement is in the foreground, a conscious perception does not occur. The therapy is controversial: EMDR is considered by some clinical psychologists as a pseudoscience or as falsified.