Hering's law of equal innervation is used to explain the conjugacy of saccadiceye movement in stereoptic animals. The law proposes that conjugacy of saccades is due to innate connections in which the eye muscles responsible for each eye's movements are innervated equally. The law also states that apparent monocular eye movements are actually the summation of conjugate version and disjunctive (or vergence) eye movements. The law was put forward by Ewald Hering in the 19th century,[1] though the underlying principles of the law date back considerably. Aristotle had commented upon this phenomenon and Ptolemy put forward a theory of why such a physiological law might be useful.[2][3] It was clearly stated for the first time by Alhacen in his Book of Optics (1021).[4]
Depiction of predictions for refoveating Muller's stimulus with eyes moving independently or eyes following Hering's law of equal innervation
Hering's law of equal innervation is best understood with Johannes Peter Müller's stimulus where an observer refoveates a point that moved in one eye only. The least-effort way to refoveate is to move the misaligned eye only. Instead Hering's law predicts that because both eyes must move by equal amounts, a combination of conjunctive and disjunctive eye movements is required to refoveate the target point. Yarbus[5] showed experimentally that binocular eyes movements are indeed composed mostly of combinations of saccades and vergence. However, it is now known that clear deviations from Hering's law also occur.[6][7][8]
This theory is in contrast to the theory proposed by Hermann von Helmholtz[9] which states that conjugacy is a learned, coordinated response and that the movements of the eyes are individually controlled. Helmholtz's point of view is today often caricatured as a chameleon-like, independent, control of the eyes although Helmholtz never defended that theory. Their disagreement concerned the innate vs. learned aspect of binocularly coordinated eye movements. Helmholtz's arguments were mainly related to Listing's law and can be simplified as the fact that there exist positions of the eyes where muscles will have different effects on the two eyes. Thus Hering's law, in its original formulation, simply cannot be correct as it would lead to situations where the eyes would move by different amounts, something on which both agreed never happens. Hering subsequently modified his law to state that the eyes behave as if they received equal innervation.
The extent to which Hering's law is correct, or not, remains in debate today, as the exact physiological underpinnings of vergence eye movements remain to be found.[10]
Notes
↑ Hering, Ewald (1977). The theory of binocular vision. New York: Plenum Press. ISBN0-306-31016-3.
↑ Howard, I. P.; Wade, N. J. (1996). "Ptolemy's contributions to the geometry of binocular vision". Perception. 25 (10): 1189–201. doi:10.1068/p251189. PMID9027922.
↑ Howard, Ian P. (1996). "Alhazen's neglected discoveries of visual phenomena". Perception. 25 (10): 1203–17. doi:10.1068/p251203. PMID9027923.
↑ Yarbus, A. L. (1967). Eye Movements and Vision. New York: Plenum Press.
↑ Pickwell LD (September 1972). "Hering's law of equal innervation and the position of the binoculus". Vision Res. 12 (9): 1499–507. doi:10.1016/0042-6989(72)90175-7. PMID5073145.
↑ Bahill AT, Ciuffreda KJ, Kenyon R, Stark L (December 1976). "Dynamic and static violations of Hering's law of equal innervation". Am J Optom Physiol Opt. 53 (12): 786–96. doi:10.1097/00006324-197612000-00005. PMID1015527.
↑ Helmholtz, H. (1910). Treatise on Physiological Optics. New York: Dover. ISBN1-85506-831-1.
↑ Michael J. Aminoff, Robert B. Daroff, ed. (2014). "Hering, Ewald". Encyclopedia of the Neurological Sciences, Volume 1. Elsevier Science. p.552. ISBN9780123851581.
Sources
Hering, Ewald (1977). Stark, Lawrence; Bridgeman, Bruce (eds.). The theory of binocular vision. Bridgeman, Bruce. New York: Plenum Press. ISBN0-306-31016-3.
Helmholtz, H. (1910). Treatise on Physiological Optics. New York: Dover. ISBN1-85506-831-1.
Yarbus, A. L. (1967). Eye Movements and Vision. New York: Plenum Press.
Pickwell LD (September 1972). "Hering's law of equal innervation and the position of the binoculus". Vision Res. 12 (9): 1499–507. doi:10.1016/0042-6989(72)90175-7. PMID5073145.
Bahill AT, Ciuffreda KJ, Kenyon R, Stark L (December 1976). "Dynamic and static violations of Hering's law of equal innervation". Am J Optom Physiol Opt. 53 (12): 786–96. doi:10.1097/00006324-197612000-00005. PMID1015527.
Karl Ewald Konstantin Hering was a German physiologist who did much research into color vision, binocular perception and eye movements. He proposed opponent color theory in 1892.
A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. In contrast, in smooth pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who 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.
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an animal has eyes on opposite sides of its head and shares no field of view between them, like in some animals.
An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus.
Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye.
The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including part of the accommodation-vergence reflex, but it can also be consciously controlled. Mammals, birds and reptiles vary their eyes' optical power by changing the form of the elastic lens using the ciliary body. Fish and amphibians vary the power by changing the distance between a rigid lens and the retina with muscles.
The horopter was originally defined in geometric terms as the locus of points in space that make the same angle at each eye with the fixation point, although more recently in studies of binocular vision it is taken to be the locus of points in space that have the same disparity as fixation. This can be defined theoretically as the points in space that project on corresponding points in the two retinas, that is, on anatomically identical points. The horopter can be measured empirically in which it is defined using some criterion.
Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms to fixate, inspect and track visual objects of interests. A special type of eye movement, rapid eye movement, occurs during REM sleep.
A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.
Fixation disparity is a tendency of the eyes to drift in the direction of the heterophoria. While the heterophoria refers to a fusion-free vergence state, the fixation disparity refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. The misalignment may be vertical, horizontal or both. The misalignment is much smaller than that of strabismus. While strabismus prevents binocular vision, fixation disparity keeps binocular vision, however it may reduce a patient's level of stereopsis. A patient may or may not have fixation disparity and a patient may have a different fixation disparity at distance than near. Observers with a fixation disparity are more likely to report eye strain in demanding visual tasks; therefore, tests of fixation disparity belong to the diagnostic tools used by eye care professionals: remediation includes vision therapy, prism eye glasses, or visual ergonomics at the workplace.
Alfred Lukyanovich Yarbus was a Soviet psychologist who studied eye movements in the 1950s and 1960s.
Fixation or visual fixation is the maintaining of the gaze on a single location. An animal can exhibit visual fixation if it possess a fovea in the anatomy of their eye. The fovea is typically located at the center of the retina and is the point of clearest vision. The species in which fixational eye movement has been verified thus far include humans, primates, cats, rabbits, turtles, salamanders, and owls. Regular eye movement alternates between saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appears to have developed for hunting prey. The term "fixation" can either be used to refer to the point in time and space of focus or the act of fixating. Fixation, in the act of fixating, is the point between any two saccades, during which the eyes are relatively stationary and virtually all visual input occurs. In the absence of retinal jitter, a laboratory condition known as retinal stabilization, perceptions tend to rapidly fade away. To maintain visibility, the nervous system carries out a procedure called fixational eye movement, which continuously stimulates neurons in the early visual areas of the brain responding to transient stimuli. There are three categories of fixational eye movement: microsaccades, ocular drifts, and ocular microtremor. At small amplitudes the boundaries between categories become unclear, particularly between drift and tremor.
Eye movement in reading involves the visual processing of written text. This was 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 (saccades) 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 recordings of eye movement and event-related potential.
Listing's law, named after German mathematician Johann Benedict Listing (1808–1882), describes the three-dimensional orientation of the eye and its axes of rotation. Listing's law has been shown to hold when the head is stationary and upright and gaze is directed toward far targets, i.e., when the eyes are either fixating, making saccades, or pursuing moving visual targets.
In human visual perception, the visual angle, denoted θ, subtended by a viewed object sometimes looks larger or smaller than its actual value. One approach to this phenomenon posits a subjective correlate to the visual angle: the perceived visual angle or perceived angular size. An optical illusion where the physical and subjective angles differ is then called a visual angle illusion or angular size illusion.
Visual perception is the ability to interpret the surrounding environment through photopic vision, color vision, scotopic vision, and mesopic vision, using light in the visible spectrum reflected by objects in the environment. This is different from visual acuity, which refers to how clearly a person sees. A person can have problems with visual perceptual processing even if they have 20/20 vision.
Instrument myopia, is a form of myopia that occurs when someone is looking into an optical instrument such as a microscope. The person focusses his or her eyes closer than needed for the image produced by the instrument.
Hering's law of visual direction describes the perceived visual direction of a point relative to an observer. Because the eyes are horizontally apart in the head, by about 6cm, the visual scene is seen from slightly different point of view by each eye. Thus comes the question of where a point is perceived, relative to the observer, when seen with either eye alone or binocularly. In 1879 Ewald Hering stated the following law: "For any given two corresponding lines of direction, or visual lines, there is in visual space a single visual direction upon which appears everything which actually lies in the pair of visual lines". Prior to Hering, both Alhazen (1021) and Wells (1792) addressed a similar questions but proposed slightly incorrect laws.
The Hering–Hillebrand deviation describes the mismatch between the theoretical and empirical horopter. The horopter is the set of points that projects at the same location in the two retinae. Geometrically the horopter is a circle passing through the nodal point of the two eyes and through the fixation point. This is known as the horizontal geometrical horopter, or as the Vieth–Müller circle. This is the set of points that correspond geometrically to the intersection between visual lines at identical eccentricities. There is also a vertical horopter which the a straight line on the sagittal plane and passing through the intersection between the sagittal plane and the Vieth–Müller circle.
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