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158-532: The visual system performs a number of complex tasks based on the image forming functionality of the eye, including the formation of monocular images, the neural mechanisms underlying stereopsis and assessment of distances to ( depth perception ) and between objects, motion perception , pattern recognition , accurate motor coordination under visual guidance, and colour vision . Together, these facilitate higher order tasks, such as object identification . The neuropsychological side of visual information processing

316-771: A REM rebound , which refers to an increase in the time spent in REM stage over normal levels. These findings are consistent with the idea that REM sleep is biologically necessary. However, the "rebound" REM sleep usually does not last fully as long as the estimated length of the missed REM periods. After the deprivation is complete, mild psychological disturbances, such as anxiety , irritability , hallucinations , and difficulty concentrating may develop and appetite may increase. There are also positive consequences of REM deprivation. Some symptoms of depression are found to be suppressed by REM deprivation; aggression may increase, and eating behavior may get disrupted. Higher norepinepherine

474-539: A 24-hour day in REM sleep. Sleeping reptiles do not seem to have PGO waves or the localized brain activation seen in mammalian REM. However, they do exhibit sleep cycles with phases of REM-like electrical activity measurable by EEG. A recent study found periodic eye movements in the central bearded dragon of Australia, leading its authors to speculate that the common ancestor of amniotes may therefore have manifested some precursor to REMS. Observations of jumping spiders in their nocturnal resting position also suggest

632-449: A 3D image is perceived in case stereovision is present. This can be achieved by means of vectographs (visible with polarized glasses), anaglyphs (visible with red-green glasses), lenticular lenses (visible with the naked eye), or head-mounted display technology. The type of changes from one eye to the other may differ depending on which level of stereoacuity is to be detected. A series of stereotests for selected levels thus constitutes

790-500: A REM sleep-like state characterized by bouts of twitching and retinal movements and hints of muscle atonia (legs curling up as a result of pressure loss caused by muscle atonia in the prosoma). Sleep deprivation experiments on non-human animals can be set up differently than those on humans. The "flower pot" method involves placing a laboratory animal above water on a platform so small that it falls off upon losing muscle tone. The naturally rude awakening which results may elicit changes in

948-416: A bigger role than either of the two other intrinsic mechanisms. The clarity with which an individual can see his environment, as well as the size of the visual field, the susceptibility of the individual to light and glare, and poor depth perception play important roles in providing a feedback loop to the brain on the body's movement through the environment. Anything that affects any of these variables can have

1106-443: A case has been made that Rembrandt may have been stereoblind . Stereopsis was first explained by Charles Wheatstone in 1838: "… the mind perceives an object of three dimensions by means of the two dissimilar pictures projected by it on the two retinæ …". He recognized that because each eye views the visual world from slightly different horizontal positions, each eye's image differs from the other. Objects at different distances from

1264-532: A cat (indicating that there is ability of stereopsis of 1200 seconds of arc of retinal disparity), a star (600 seconds of arc) and a car (550 seconds of arc). To standardize the results, the image should be viewed at a distance from the eye of 40 cm and exactly in the frontoparallel plane. While most random dot stereotest like the Random Dot "E" Stereotest or TNO-Stereotest will require specific spectacles for testing (i.e. with polarized or red-green glasses),

1422-510: A complex brain process such as REM sleep indicates that it serves an important function for the survival of mammalian and avian species. It fulfills important physiological needs vital for survival to the extent that prolonged REM sleep deprivation leads to death in experimental animals. In both humans and experimental animals, REM sleep loss leads to several behavioral and physiological abnormalities. Loss of REM sleep has been noticed during various natural and experimental infections. Survivability of

1580-442: A different route to perception . Another population sends information to the superior colliculus in the midbrain , which assists in controlling eye movements ( saccades ) as well as other motor responses. A final population of photosensitive ganglion cells , containing melanopsin for photosensitivity , sends information via the retinohypothalamic tract to the pretectum ( pupillary reflex ), to several structures involved in

1738-404: A drug-free baseline week, 19 days on either paroxetine or fluvoxamine with morning and evening doses, and 5 days of absolute discontinuation. Results showed that SSRI treatment decreased the average amount of dream recall frequency in comparison to baseline measurements as a result of serotonergic REM suppression. Fluvoxamine increased the length of dream reporting, bizarreness of dreams as well as

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1896-438: A flat wall. Had he chosen any other near object, he might have discovered horizontal disparity of its features. His column was one of the few objects that projects identical images of itself in the two eyes. Stereoscopy became popular during Victorian times with the invention of the prism stereoscope by David Brewster . This, combined with photography , meant that tens of thousands of stereograms were produced. Until about

2054-493: A higher proportion of REM sleep. The transition to REM sleep brings marked physical changes, beginning with electrical bursts called "ponto-geniculo-occipital waves" ( PGO waves ) originating in the brain stem . REM sleep occurs 4 times in a 7-hour sleep. Organisms in REM sleep suspend central homeostasis , allowing large fluctuations in respiration , thermoregulation and circulation which do not occur in any other modes of sleeping or waking. The body abruptly loses muscle tone,

2212-421: A human, the eyes change their angle according to the distance to the observed object. To a computer this represents significant extra complexity in the geometrical calculations ( epipolar geometry ). In fact the simplest geometrical case is when the camera image planes are on the same plane. The images may alternatively be converted by reprojection through a linear transformation to be on the same image plane. This

2370-405: A key capability for success in modern society. Nonetheless, there are indications that the lack of stereo vision may lead persons to compensate by other means: in particular, stereo blindness may give people an advantage when depicting a scene using monocular depth cues of all kinds, and among artists there appear to be a disproportionately high number of persons lacking stereopsis. In particular,

2528-447: A lesser extent the vertebrate visual system. Together, the cornea and lens refract light into a small image and shine it on the retina . The retina transduces this image into electrical pulses using rods and cones . The optic nerve then carries these pulses through the optic canal . Upon reaching the optic chiasm the nerve fibers decussate (left becomes right). The fibers then branch and terminate in three places. Most of

2686-420: A light-sensitive medium. In the case of the camera, this medium is film or an electronic sensor; in the case of the eye, it is an array of visual receptors. With this simple geometrical similarity, based on the laws of optics, the eye functions as a transducer , as does a CCD camera . In the visual system, retinal , technically called retinene 1 or "retinaldehyde", is a light-sensitive molecule found in

2844-410: A modest REM rebound . Techniques of neurosurgery , chemical injection, electroencephalography , positron emission tomography , and reports of dreamers upon waking have all been used to study this phase of sleep. REM sleep is called "paradoxical" because of its similarities to wakefulness . Although the body is paralyzed, the brain acts as if it is somewhat awake, with cerebral neurons firing with

3002-399: A negative effect on balance and maintaining posture. This effect has been seen in research involving elderly subjects when compared to young controls, in glaucoma patients compared to age matched controls, cataract patients pre and post surgery, and even something as simple as wearing safety goggles. Monocular vision (one eyed vision) has also been shown to negatively impact balance, which

3160-447: A newborn, detect nearsightedness and astigmatism , and evaluate the eye teaming and alignment. Visual acuity improves from about 20/400 at birth to approximately 20/25 at 6 months of age. This happens because the nerve cells in the retina and brain that control vision are not fully developed. Depth perception , focus, tracking and other aspects of vision continue to develop throughout early and middle childhood. From recent studies in

3318-460: A night's sleep. The first REM episode occurs about 70 minutes after falling asleep. Cycles of about 90 minutes each follow, with each cycle including a larger proportion of REM sleep. (The increased REM sleep later in the night is connected with the circadian rhythm and occurs even in people who did not sleep in the first part of the night.) In the weeks after a human baby is born, as its nervous system matures, neural patterns in sleep begin to show

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3476-438: A notebook with a built in stereoscopic LCD. Although older technology required the user to don goggles or visors for viewing computer-generated images , or CGI, newer technology tends to employ Fresnel lenses or plates over the liquid crystal displays, freeing the user from the need to put on special glasses or goggles . In stereopsis tests (short: stereotests ), slightly different images are shown to each eye, such that

3634-584: A particular object. Along with this increasing complexity of neural representation may come a level of specialization of processing into two distinct pathways: the dorsal stream and the ventral stream (the Two Streams hypothesis , first proposed by Ungerleider and Mishkin in 1982). The dorsal stream, commonly referred to as the "where" stream, is involved in spatial attention (covert and overt), and communicates with regions that control eye movements and hand movements. More recently, this area has been called

3792-401: A positive impact on exercising practical tasks such as needle-threading, ball-catching (especially in fast ball games ), pouring liquids, and others. Professional activity may involve operating stereoscopic instruments such as a binocular microscope . While some of these tasks may profit from compensation of the visual system by means of other depth cues, there are some roles for which stereopsis

3950-494: A problem for stereopsis, the correspondence problem . This is that any dot in one half image can realistically be paired with many same-coloured dots in the other half image. Our visual systems clearly solve the correspondence problem, in that we see the intended depth instead of a fog of false matches. Research began to understand how. Also in the 1960s, Horace Barlow , Colin Blakemore , and Jack Pettigrew found neurons in

4108-462: A real three-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy . The perception of depth in such cases is also referred to as "stereoscopic depth". The perception of depth and three-dimensional structure is, however, possible with information visible from one eye alone, such as differences in object size and motion parallax (differences in

4266-508: A rhythm of REM and non-REM sleep. (In faster-developing mammals, this process occurs in utero.) Infants spend more time in REM sleep than adults. The proportion of REM sleep then decreases significantly in childhood. Older people tend to sleep less overall, but sleep in REM for about the same absolute time (and therefore spend a greater proportion of sleep in REM). Rapid eye movement sleep can be subclassified into tonic and phasic modes. Tonic REM

4424-448: A shift of gaze in dream imagery. Against this hypothesis is that such eye movements occur in those born blind and in fetuses in spite of lack of vision. Also, binocular REMs are non-conjugated (i.e., the two eyes do not point in the same direction at a time) and so lack a fixation point . In support of this theory, research finds that in goal-oriented dreams, eye gaze is directed towards the dream action, determined from correlations in

4582-404: A shrapnel injury to the brainstem did not find the individual's memory to be impaired. Antidepressants, which suppress REM sleep, show no evidence of impairing memory and may improve it. Graeme Mitchison and Francis Crick proposed in 1983 that by virtue of its inherent spontaneous activity, the function of REM sleep "is to remove certain undesirable modes of interaction in networks of cells in

4740-435: A square matrix of about 10,000 small dots, with each dot having a 50% probability of being black or white. No recognizable objects could be seen in either half image. The two half images of a random-dot stereogram were essentially identical, except that one had a square area of dots shifted horizontally by one or two dot diameters, giving horizontal disparity. The gap left by the shifting was filled in with new random dots, hiding

4898-466: A state known as REM atonia. In 1953, Professor Nathaniel Kleitman and his student Eugene Aserinsky defined rapid eye movement and linked it to dreams. REM sleep was further described by researchers, including William Dement and Michel Jouvet . Many experiments have involved awakening test subjects whenever they begin to enter the REM phase, thereby producing a state known as REM deprivation. Subjects allowed to sleep normally again usually experience

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5056-421: A stereoscope, but relied on viewers using a form of free fusion so that each eye views different images – were introduced. Stereopsis appears to be processed in the visual cortex of mammals in binocular cells having receptive fields in different horizontal positions in the two eyes. Such a cell is active only when its preferred stimulus is in the correct position in the left eye and in the correct position in

5214-464: A study found a positive impact of stereopsis in specific situations at intermediate distances only; furthermore, a study on elderly persons found that glare , visual field loss, and useful field of view were significant predictors of crash involvement, whereas the elderly persons' values of visual acuity, contrast sensitivity, and stereoacuity were not associated with crashes. Binocular vision has further advantages aside from stereopsis, in particular

5372-426: A test of stereoacuity . There are two types of common clinical tests for stereopsis and stereoacuity: random dot stereotests and contour stereotests. Random-dot stereopsis tests use pictures of stereo figures that are embedded in a background of random dots. Contour stereotests use pictures in which the targets presented to each eye are separated horizontally. The ability of stereopsis can be tested by, for example,

5530-532: Is 11–40% lower. Neural activity during REM sleep seems to originate in the brain stem , especially the pontine tegmentum and locus coeruleus . REM sleep is punctuated and immediately preceded by PGO (ponto-geniculo-occipital) waves , bursts of electrical activity originating in the brain stem. (PGO waves have long been measured directly in cats but not in humans because of constraints on experimentation; however, comparable effects have been observed in humans during "phasic" events which occur during REM sleep, and

5688-516: Is a network of brain regions that are active when an individual is awake and at rest. The visual system's default mode can be monitored during resting state fMRI : Fox, et al. (2005) found that " the human brain is intrinsically organized into dynamic, anticorrelated functional networks" , in which the visual system switches from resting state to attention. In the parietal lobe , the lateral and ventral intraparietal cortex are involved in visual attention and saccadic eye movements. These regions are in

5846-678: Is a possible cause of these results. Whether and how long-term REM deprivation has psychological effects remains a matter of controversy. Several reports have indicated that REM deprivation increases aggression and sexual behavior in laboratory test animals. Rats deprived of paradoxical sleep die in 4–6 weeks (twice the time before death in case of total sleep deprivation). Mean body temperature falls continually during this period. It has been suggested that acute REM sleep deprivation can improve certain types of depression —when depression appears to be related to an imbalance of certain neurotransmitters. Although sleep deprivation in general annoys most of

6004-798: Is also active during REM sleep and may participate in generating the PGO waves, and experimental suppression of the amygdala results in less REM sleep. The amygdala may also regulate cardiac function in lieu of the less active insular cortex . Compared to slow-wave sleep , both waking and paradoxical sleep involve higher use of the neurotransmitter acetylcholine , which may cause the faster brainwaves. The monoamine neurotransmitters norepinephrine , serotonin and histamine are completely unavailable. Injections of acetylcholinesterase inhibitor , which effectively increases available acetylcholine, have been found to induce paradoxical sleep in humans and other animals already in slow-wave sleep. Carbachol , which mimics

6162-454: Is called image rectification . Computer stereo vision with many cameras under fixed lighting is called structure from motion . Techniques using a fixed camera and known lighting are called photometric stereo techniques, or " shape from shading ". Many attempts have been made to reproduce human stereo vision on rapidly changing computer displays, and toward this end numerous patents relating to 3D television and cinema have been filed in

6320-532: Is characterized by theta rhythms in the brain; phasic REM is characterized by PGO waves and actual "rapid" eye movements. Processing of external stimuli is heavily inhibited during phasic REM, and recent evidence suggests that sleepers are more difficult to arouse from phasic REM than in slow-wave sleep. Selective REMS deprivation causes a significant increase in the number of attempts to go into REM stage while asleep. On recovery nights, an individual will usually move to stage 3 and REM sleep more quickly and experience

6478-469: Is clouding of the lens, which in turn affects vision. Although it may be accompanied by yellowing, clouding and yellowing can occur separately. This is typically a result of ageing, disease, or drug use. Stereopsis Stereopsis (from Ancient Greek στερεός ( stereós )  'solid' and ὄψις ( ópsis )  'appearance, sight') is the component of depth perception retrieved through binocular vision . Stereopsis

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6636-409: Is imperative. Occupations requiring the precise judgment of distance sometimes include a requirement to demonstrate some level of stereopsis; in particular, there is such a requirement for aeroplane pilots (even if the first pilot to fly around the world alone, Wiley Post , accomplished his feat with monocular vision only.) Also surgeons normally demonstrate high stereo acuity. As to car driving ,

6794-425: Is known as visual perception , an abnormality of which is called visual impairment , and a complete absence of which is called blindness . The visual system also has several non-image forming visual functions, independent of visual perception, including the pupillary light reflex and circadian photoentrainment . This article describes the human visual system, which is representative of mammalian vision , and to

6952-548: Is known to have a potential socioeconomic impact on children and adults. In particular, both large-angle and small-angle strabismus can negatively affect self-esteem , as it interferes with normal eye contact , often causing embarrassment, anger, and feelings of awkwardness. For further details on this, see psychosocial effects of strabismus . It has been noted that with the growing introduction of 3D display technology in entertainment and in medical and scientific imaging, high quality binocular vision including stereopsis may become

7110-443: Is limited by the level of visual acuity of the poorer eye. In particular, patients who have comparatively lower visual acuity tend to need relatively larger spatial frequencies to be present in the input images, else they cannot achieve stereopsis. Fine stereopsis requires both eyes to have a good visual acuity in order to detect small spatial differences, and is easily disrupted by early visual deprivation. There are indications that in

7268-435: Is linked to the precision with which depth is derived, and that a conscious awareness of this precision – perceived as an impression of interactability and realness – may help guide the planning of motor action. There are two distinct aspects to stereopsis: coarse stereopsis and fine stereopsis, and provide depth information of different degree of spatial and temporal precision. The stereopsis which an individual can achieve

7426-500: Is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image because they are in slightly different positions in one's head (left and right eyes). These positional differences are referred to as "horizontal disparities" or, more generally, " binocular disparities ". Disparities are processed in the visual cortex of the brain to yield depth perception . While binocular disparities are naturally present when viewing

7584-788: Is not well regulated during REM sleep, and thus organisms become more sensitive to temperatures outside their thermoneutral zone . Cats and other small furry mammals will shiver and breathe faster to regulate temperature during NREMS—but not during REMS. With the loss of muscle tone, animals lose the ability to regulate temperature through body movement. (However, even cats with pontine lesions preventing muscle atonia during REM did not regulate their temperature by shivering.) Neurons that typically activate in response to cold temperatures—triggers for neural thermoregulation—simply do not fire during REM sleep, as they do in NREM sleep and waking. Consequently, hot or cold environmental temperatures can reduce

7742-423: Is often one of the first senses affected by aging. A number of changes occur with aging: Along with proprioception and vestibular function , the visual system plays an important role in the ability of an individual to control balance and maintain an upright posture. When these three conditions are isolated and balance is tested, it has been found that vision is the most significant contributor to balance, playing

7900-609: Is one of the treatments for people lacking in stereopsis. Vision therapy will allow individuals to enhance their vision through several exercises such as by strengthening and improving eye movement. There is recent evidence that stereoacuity may be improved in persons with amblyopia by means of perceptual learning ( see also: treatment of amblyopia ). Stereopsis has been found in many vertebrates including mammals such as horses , birds such as falcons and owls , reptiles, amphibia including toads and fish. It has also been found in invertebrates including, cephalopods like

8058-517: Is seven unique nuclei . Anterior, posterior and medial pretectal nuclei inhibit pain (indirectly), aid in REM , and aid the accommodation reflex , respectively. The Edinger-Westphal nucleus moderates pupil dilation and aids (since it provides parasympathetic fibers) in convergence of the eyes and lens adjustment. Nuclei of the optic tract are involved in smooth pursuit eye movement and the accommodation reflex, as well as REM. The suprachiasmatic nucleus

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8216-457: Is that the PGO electrical waves, which precede the eye movements, also influence memory. REM sleep could provide a unique opportunity for "unlearning" to occur in the basic neural networks involved in homeostasis, which are protected from this "synaptic downscaling" effect during deep sleep. REM sleep prevails most after birth, and diminishes with age. According to the "ontogenetic hypothesis", REM (also known in neonates as active sleep ) aids

8374-443: Is the region of the hypothalamus that halts production of melatonin (indirectly) at first light. These are components of the visual pathway , also called the optic pathway , that can be divided into anterior and posterior visual pathways . The anterior visual pathway refers to structures involved in vision before the lateral geniculate nucleus . The posterior visual pathway refers to structures after this point. Light entering

8532-519: The efficient coding hypothesis in 1961 as a theoretical model of sensory coding in the brain . Limitations in the applicability of this theory in the primary visual cortex (V1) motivated the V1 Saliency Hypothesis that V1 creates a bottom-up saliency map to guide attention exogenously. With attentional selection as a center stage, vision is seen as composed of encoding, selection, and decoding stages. The default mode network

8690-497: The ExoMars Rover and surgical robotics. Two cameras take pictures of the same scene, but they are separated by a distance – exactly like our eyes. A computer compares the images while shifting the two images together over top of each other to find the parts that match. The shifted amount is called the disparity . The disparity at which objects in the image best match is used by the computer to calculate their distance. For

8848-470: The Lang-Stereotest , which consists of a random-dot stereogram upon which a series of parallel strips of cylindrical lenses are imprinted in certain shapes, which separate the views seen by each eye in these areas, similarly to a hologram . Without stereopsis, the image looks only like a field of random dots, but the shapes become discernible with increasing stereopsis, and generally consists of

9006-607: The USPTO . At least in the US, commercial activity involving those patents has been confined exclusively to the grantees and licensees of the patent holders, whose interests tend to last for twenty years from the time of filing. Discounting 3D television and cinema (which generally require more than one digital projector whose moving images are mechanically coupled, in the case of IMAX 3D cinema), several stereoscopic LCDs are going to be offered by Sharp , which has already started shipping

9164-509: The United States and Australia there is some evidence that the amount of time school aged children spend outdoors, in natural light, may have some impact on whether they develop myopia . The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. More prominent myopia (nearsightedness) and astigmatism are thought to be inherited. Children with this condition may need to wear glasses. Vision

9322-425: The body clock mechanism, is probably not involved in conscious vision, as these RGC do not project to the lateral geniculate nucleus but to the pretectal olivary nucleus .) An opsin absorbs a photon (a particle of light) and transmits a signal to the cell through a signal transduction pathway , resulting in hyper-polarization of the photoreceptor. Rods and cones differ in function. Rods are found primarily in

9480-473: The cat visual cortex that had their receptive fields in different horizontal positions in the two eyes. This established the neural basis for stereopsis. Their findings were disputed by David Hubel and Torsten Wiesel , although they eventually conceded when they found similar neurons in the monkey visual cortex. In the 1980s, Gian Poggio and others found neurons in V2 of the monkey brain that responded to

9638-464: The chromophore retinal has a bent shape called cis-retinal (referring to a cis conformation in one of the double bonds). When light interacts with the retinal, it changes conformation to a straight form called trans-retinal and breaks away from the opsin. This is called bleaching because the purified rhodopsin changes from violet to colorless in the light. At baseline in the dark, the rhodopsin absorbs no light and releases glutamate , which inhibits

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9796-424: The cortex ; patterns of EEG activity similar to these rhythms are also observed during wakefulness. The cortical and thalamic neurons in the waking and REM sleeping brain are more depolarized (fire more readily) than in the NREM deep sleeping brain. Human theta wave activity predominates during REM sleep in both the hippocampus and the cortex. During REM sleep, electrical connectivity among different parts of

9954-402: The cuttlefish , crustaceans, spiders, and insects such as mantis . Stomatopods even have stereopsis with just one eye. Rapid eye movement sleep Rapid eye movement sleep ( REM sleep or REMS ) is a unique phase of sleep in mammals (including humans ) and birds , characterized by random rapid movement of the eyes , accompanied by low muscle tone throughout the body, and

10112-418: The developing brain by providing the neural stimulation that newborns need to form mature neural connections. Sleep deprivation studies have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, and decreased brain mass. The strongest evidence for the ontogenetic hypothesis comes from experiments on REM deprivation, and from the development of the visual system in

10270-440: The dual-process hypothesis of sleep and memory, the two major phases of sleep correspond to different types of memory. "Night half" studies have tested this hypothesis with memory tasks either begun before sleep and assessed in the middle of the night, or begun in the middle of the night and assessed in the morning. Slow-wave sleep , part of non-REM sleep, appears to be important for declarative memory . Artificial enhancement of

10428-436: The field of view from both eyes, and similarly for the left brain. A small region in the center of the field of view is processed redundantly by both halves of the brain. Information from the right visual field (now on the left side of the brain) travels in the left optic tract. Information from the left visual field travels in the right optic tract. Each optic tract terminates in the lateral geniculate nucleus (LGN) in

10586-527: The inferior temporal cortex . V4 recognizes simple shapes, and gets input from V1 (strong), V2, V3, LGN, and pulvinar. V5's outputs include V4 and its surrounding area, and eye-movement motor cortices ( frontal eye-field and lateral intraparietal area ). V5's functionality is similar to that of the other V's, however, it integrates local object motion into global motion on a complex level. V6 works in conjunction with V5 on motion analysis. V5 analyzes self-motion, whereas V6 analyzes motion of objects relative to

10744-399: The intraparietal sulcus (marked in red in the adjacent image). Newborn infants have limited color perception . One study found that 74% of newborns can distinguish red, 36% green, 25% yellow, and 14% blue. After one month, performance "improved somewhat." Infant's eyes do not have the ability to accommodate . Pediatricians are able to perform non-verbal testing to assess visual acuity of

10902-414: The lateral geniculate nucleus and primary visual cortex . Ioannis Tsoukalas of Stockholm University has hypothesized that REM sleep is an evolutionary transformation of a well-known defensive mechanism, the tonic immobility reflex. This reflex, also known as animal hypnosis or death feigning, functions as the last line of defense against an attacking predator and consists of the total immobilization of

11060-472: The neocortex , while lower levels of acetylcholine and norepinephrine in the neocortex encourage the uncontrolled spread of associational activity within neocortical areas. This is in contrast to waking consciousness, where higher levels of norepinephrine and acetylcholine inhibit recurrent connections in the neocortex. REM sleep through this process adds creativity by allowing "neocortical structures to reorganise associative hierarchies, in which information from

11218-689: The neurotransmitter acetylcholine , combined with a nearly complete absence of monoamine neurotransmitters histamine, serotonin and norepinephrine . Experiences of REM sleep are not transferred to permanent memory due to absence of norepinephrine. REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep (NREM sleep, NREMS, synchronized sleep). The absence of visual and auditory stimulation ( sensory deprivation ) during REM sleep can cause hallucinations . REM and non-REM sleep alternate within one sleep cycle, which lasts about 90 minutes in adult humans. As sleep cycles continue, they shift towards

11376-432: The optic nerve . Different populations of ganglion cells in the retina send information to the brain through the optic nerve. About 90% of the axons in the optic nerve go to the lateral geniculate nucleus in the thalamus . These axons originate from the M, P, and K ganglion cells in the retina, see above. This parallel processing is important for reconstructing the visual world; each type of information will go through

11534-425: The stereoscope . Leonardo da Vinci had also realized that objects at different distances from the eyes project images in the two eyes that differ in their horizontal positions, but had concluded only that this made it impossible for a painter to portray a realistic depiction of the depth in a scene from a single canvas. Leonardo chose for his near object a column with a circular cross section and for his far object

11692-475: The visual field of the eye, all the way through the optic tract to a nerve position in V1 up to V4, i.e. the primary visual areas. After that, the visual pathway is roughly separated into a ventral and dorsal pathway . The visual cortex is responsible for processing the visual image. It lies at the rear of the brain (highlighted in the image), above the cerebellum . The region that receives information directly from

11850-403: The "how" stream to emphasize its role in guiding behaviors to spatial locations. The ventral stream, commonly referred to as the "what" stream, is involved in the recognition, identification and categorization of visual stimuli. However, there is still much debate about the degree of specialization within these two pathways, since they are in fact heavily interconnected. Horace Barlow proposed

12008-430: The 1960s, research into stereopsis was dedicated to exploring its limits and its relationship to singleness of vision. Researchers included Peter Ludvig Panum , Ewald Hering , Adelbert Ames Jr. , and Kenneth N. Ogle . In the 1960s, Bela Julesz invented random-dot stereograms . Unlike previous stereograms, in which each half image showed recognizable objects, each half image of the first random-dot stereograms showed

12166-504: The 1990s using positron emission tomography (PET) confirmed the role of the brain stem and suggested that, within the forebrain , the limbic and paralimbic systems showed more activation than other areas. The areas activated during REM sleep are approximately inverse to those activated during non-REM sleep and display greater activity than in quiet waking. The "anterior paralimbic REM activation area" (APRA) includes areas linked with emotion , memory, fear and sex, and may thus relate to

12324-458: The ED is from a psychological rather than a physiological cause. In females, erection of the clitoris ( nocturnal clitoral tumescence or NCT) causes enlargement, with accompanying vaginal blood flow and transudation (i.e. lubrication). During a normal night of sleep, the penis and clitoris may be erect for a total time of from one hour to as long as three and a half hours during REM. Body temperature

12482-485: The K cells (color) in the retina. The neurons of the LGN then relay the visual image to the primary visual cortex (V1) which is located at the back of the brain ( posterior end ) in the occipital lobe in and close to the calcarine sulcus . The LGN is not just a simple relay station, but it is also a center for processing; it receives reciprocal input from the cortical and subcortical layers and reciprocal innervation from

12640-411: The LGN connect to the M cells and P ( parvocellular ) cells of the optic nerve for the same side of the brain as its respective LGN. Spread out, the six layers of the LGN are the area of a credit card and about three times its thickness. The LGN is rolled up into two ellipsoids about the size and shape of two small birds' eggs. In between the six layers are smaller cells that receive information from

12798-439: The LGN is called the primary visual cortex (also called V1 and striate cortex). It creates a bottom-up saliency map of the visual field to guide attention or eye gaze to salient visual locations. Hence selection of visual input information by attention starts at V1 along the visual pathway. Visual information then flows through a cortical hierarchy. These areas include V2, V3, V4 and area V5/MT. (The exact connectivity depends on

12956-799: The Lang-Stereotest works without the use special spectacles, thereby facilitating the use in young children. Examples of contour stereotests are the Titmus stereotests, the most well-known example being the Titmus fly stereotest, where a picture of a fly is displayed with disparities on the edges. The patient uses a 3-D glasses to look at the picture and determine whether a 3-D figure can be seen. The amount of disparity in images vary, such as 400-100 sec of arc, and 800-40 sec arc. Deficiency in stereopsis can be complete (then called stereoblindness ) or more or less impaired. Causes include blindness in one eye, amblyopia and strabismus . Vision therapy

13114-521: The REM-on neurons. McCarley and Hobson suggested that the REM-on neurons actually stimulate REM-off neurons, thereby serving as the mechanism for the cycling between REM and non-REM sleep. They used Lotka–Volterra equations to describe this cyclical inverse relationship. Kayuza Sakai and Michel Jouvet advanced a similar model in 1981. Whereas acetylcholine manifests in the cortex equally during wakefulness and REM, it appears in higher concentrations in

13272-488: The abundance of acetylcholine in the brainstem) and perhaps from mechanisms used in waking muscle inhibition. The medulla oblongata , located between pons and spine, seems to have the capacity for organism-wide muscle inhibition. Some localized twitching and reflexes can still occur. Pupils contract. Lack of REM atonia causes REM behavior disorder , where those affected physically act out their dreams, or conversely "dream out their acts", under an alternative theory on

13430-404: The animal so that it appears dead . Tsoukalas argues that the neurophysiology and phenomenology of this reaction shows striking similarities to REM sleep; for example, both reactions exhibit brainstem control, cholinergic neurotransmission, paralysis, hippocampal theta rhythm, and thermoregulatory changes. According to "scanning hypothesis", the directional properties of REM sleep are related to

13588-406: The background. V6's primary input is V1, with V5 additions. V6 houses the topographical map for vision. V6 outputs to the region directly around it (V6A). V6A has direct connections to arm-moving cortices, including the premotor cortex . The inferior temporal gyrus recognizes complex shapes, objects, and faces or, in conjunction with the hippocampus , creates new memories . The pretectal area

13746-403: The best evidence for REM's improvement of memory pertains to learning of procedures—new ways of moving the body (such as trampoline jumping), and new techniques of problem solving. REM deprivation seemed to impair declarative (i.e., factual) memory only in more complex cases, such as memories of longer stories. REM sleep apparently counteracts attempts to suppress certain thoughts. According to

13904-463: The bipolar cell. This inhibits the release of neurotransmitters from the bipolar cells to the ganglion cell. When there is light present, glutamate secretion ceases, thus no longer inhibiting the bipolar cell from releasing neurotransmitters to the ganglion cell and therefore an image can be detected. The final result of all this processing is five different populations of ganglion cells that send visual (image-forming and non-image-forming) information to

14062-440: The body, is accomplished through the inhibition of motor neurons . When the body shifts into REM sleep, motor neurons throughout the body undergo a process called hyperpolarization : their already-negative membrane potential decreases by another 2–10 millivolts , thereby raising the threshold which a stimulus must overcome to excite them. Muscle inhibition may result from unavailability of monoamine neurotransmitters (restraining

14220-406: The body. Sleep can be distributed throughout the day or clustered during one part of the rhythm: in nocturnal animals, during the day, and in diurnal animals, at night. The organism returns to homeostatic regulation almost immediately after REM sleep ends. During a night of sleep, humans usually experience about four or five periods of REM sleep; they are shorter (~15 min) at the beginning of

14378-502: The brain manifests differently than during wakefulness. Frontal and posterior areas are less coherent in most frequencies, a fact which has been cited in relation to the chaotic experience of dreaming. However, the posterior areas are more coherent with each other; as are the right and left hemispheres of the brain, especially during lucid dreams . Brain energy use in REM sleep, as measured by oxygen and glucose metabolism, equals or exceeds energy use in waking. The rate in non-REM sleep

14536-410: The brain exerts less control over breathing; electrical stimulation of respiration-linked brain areas does not influence the lungs, as it does during non-REM sleep and in waking. Erections of the penis ( nocturnal penile tumescence or NPT) normally accompany REM sleep in rats and humans. If a male has erectile dysfunction (ED) while awake, but has NPT episodes during REM, it would suggest that

14694-515: The brain stem during REM. The withdrawal of orexin and GABA may cause the absence of the other excitatory neurotransmitters; researchers in recent years increasingly include GABA regulation in their models. Most of the eye movements in "rapid eye movement" sleep are in fact less rapid than those normally exhibited by waking humans. They are also shorter in duration and more likely to loop back to their starting point. About seven such loops take place over one minute of REM sleep. In slow-wave sleep,

14852-535: The brain: A 2006 University of Pennsylvania study calculated the approximate bandwidth of human retinas to be about 8,960 kilobits per second, whereas guinea pig retinas transfer at about 875 kilobits. In 2007 Zaidi and co-researchers on both sides of the Atlantic studying patients without rods and cones, discovered that the novel photoreceptive ganglion cell in humans also has a role in conscious and unconscious visual perception. The peak spectral sensitivity

15010-491: The cerebral cortex"—a process they characterize as " unlearning ". As a result, those memories which are relevant (whose underlying neuronal substrate is strong enough to withstand such spontaneous, chaotic activation) are further strengthened, whilst weaker, transient, "noise" memory traces disintegrate. Memory consolidation during paradoxical sleep is specifically correlated with the periods of rapid eye movement, which do not occur continuously. One explanation for this correlation

15168-601: The change in electrical activity, measured by EEG, and loss of muscle tone, interspersed with bouts of twitching in phasic REM. The amount of REM sleep and cycling varies among animals; predators experience more REM sleep than prey. Larger animals also tend to stay in REM for longer, possibly because higher thermal inertia of their brains and bodies allows them to tolerate longer suspension of thermoregulation. The period (full cycle of REM and non-REM) lasts for about 90 minutes in humans, 22 minutes in cats, and 12 minutes in rats. In utero, mammals spend more than half (50–80%) of

15326-445: The chemical changes in the brain show continuous periodic oscillation. According to the activation-synthesis hypothesis proposed by Robert McCarley and Allan Hobson in 1975–1977, control over REM sleep involves pathways of "REM-on" and "REM-off" neurons in the brain stem. REM-on neurons are primarily cholinergic (i.e., involve acetylcholine); REM-off neurons activate serotonin and noradrenaline, which among other functions suppress

15484-440: The combination of motion stereopsis and no static stereopsis to be present only in exotropes , not in esotropes . There are strong indications that the stereoscopic mechanism consists of at least two perceptual mechanisms, possibly three. Coarse and fine stereopsis are processed by two different physiological subsystems, with a coarse stereopsis being derived from diplopic stimuli (that is, stimuli with disparities well beyond

15642-449: The control of circadian rhythms and sleep such as the suprachiasmatic nucleus (the biological clock), and to the ventrolateral preoptic nucleus (a region involved in sleep regulation ). A recently discovered role for photoreceptive ganglion cells is that they mediate conscious and unconscious vision – acting as rudimentary visual brightness detectors as shown in rodless coneless eyes. The optic nerves from both eyes meet and cross at

15800-903: The course of the development of the visual system in infants , coarse stereopsis may develop before fine stereopsis and that coarse stereopsis guides the vergence movements which are needed in order for fine stereopsis to develop in a subsequent stage. Furthermore, there are indications that coarse stereopsis is the mechanism that keeps the two eyes aligned after strabismus surgery . It has also been suggested to distinguish between two different types of stereoscopic depth perception: static depth perception (or static stereo perception) and motion-in-depth perception (or stereo motion perception). Some individuals who have strabismus and show no depth perception using static stereotests (in particular, using Titmus tests, see this article's section on contour stereotests ) do perceive motion in depth when tested using dynamic random dot stereograms . One study found

15958-407: The depth of random-dot stereograms. In the 1970s, Christopher Tyler invented autostereograms , random-dot stereograms that can be viewed without a stereoscope. This led to the popular Magic Eye pictures. In 1989 Antonio Medina Puerta demonstrated with photographs that retinal images with no parallax disparity but with different shadows are fused stereoscopically, imparting depth perception to

16116-416: The distance from the fixation point), and pictorial cues such as superimposition (nearer objects cover up farther objects) and familiar size (nearer objects appear bigger than farther objects). However, by using a stereoscope, researchers have been able to oppose various depth cues including stereopsis. The most drastic version of this is pseudoscopy , in which the half-images of stereograms are swapped between

16274-500: The dreamer's recent experience taken directly from episodic memory . By one estimate, 80% of dreams occur during REM. Hobson and McCarley proposed that the PGO waves characteristic of "phasic" REM might supply the visual cortex and forebrain with electrical excitement which amplifies the hallucinatory aspects of dreaming. However, people woken up during sleep do not report significantly more bizarre dreams during phasic REMS, compared to tonic REMS. Another possible relationship between

16432-519: The dreams they were experiencing, and to estimate the duration of their dreams as longer. Lucid dreams are reported far more often in REM sleep. (In fact these could be considered a hybrid state combining essential elements of REM sleep and waking consciousness.) The mental events which occur during REM most commonly have dream hallmarks including narrative structure, convincingness (e.g., experiential resemblance to waking life), and incorporation of instinctual themes. Sometimes, they include elements of

16590-427: The effect of acetylcholine on neurons, has a similar influence. In waking humans, the same injections produce paradoxical sleep only if the monoamine neurotransmitters have already been depleted. Two other neurotransmitters , orexin and gamma-Aminobutyric acid (GABA), seem to promote wakefulness, diminish during deep sleep, and inhibit paradoxical sleep. Unlike the abrupt transitions in electrical patterns,

16748-528: The enhancement of vision quality through binocular summation ; persons with strabismus (even those who have no double vision) have lower scores of binocular summation, and this appears to incite persons with strabismus to close one eye in visually demanding situations. It has long been recognized that full binocular vision, including stereopsis, is an important factor in the stabilization of post-surgical outcome of strabismus corrections. Many persons lacking stereopsis have (or have had) visible strabismus , which

16906-404: The existence of similar PGO waves is thus inferred.) These waves occur in clusters about every 6 seconds for 1–2 minutes during the transition from deep to paradoxical sleep. They exhibit their highest amplitude upon moving into the visual cortex and are a cause of the "rapid eye movements" in paradoxical sleep. Other muscles may also contract under the influence of these waves. Research in

17064-459: The experience of dreaming during REMS. More recent PET research has indicated that the distribution of brain activity during REM sleep varies in correspondence with the type of activity seen in the prior period of wakefulness. The superior frontal gyrus , medial frontal areas , intraparietal sulcus , and superior parietal cortex , areas involved in sophisticated mental activity, show equal activity in REM sleep as in wakefulness. The amygdala

17222-479: The experimental animals decreases when REM sleep is totally attenuated during infection; this leads to the possibility that the quality and quantity of REM sleep is generally essential for normal body physiology. Further, the existence of a "REM rebound" effect suggests the possibility of a biological need for REM sleep. While the precise function of REM sleep is not well understood, several theories have been proposed. Sleep in general aids memory. REM sleep may favor

17380-546: The eye is refracted as it passes through the cornea . It then passes through the pupil (controlled by the iris ) and is further refracted by the lens . The cornea and lens act together as a compound lens to project an inverted image onto the retina. The retina consists of many photoreceptor cells which contain particular protein molecules called opsins . In humans, two types of opsins are involved in conscious vision: rod opsins and cone opsins . (A third type, melanopsin in some retinal ganglion cells (RGC), part of

17538-497: The eyes can drift apart; however, the eyes of the paradoxical sleeper move in tandem. These eye movements follow the ponto-geniculo-occipital waves originating in the brain stem. The eye movements themselves may relate to the sense of vision experienced in the dream, but a direct relationship remains to be clearly established. Congenitally blind people, who do not typically have visual imagery in their dreams, still move their eyes in REM sleep. An alternative explanation suggests that

17696-416: The eyes project images in the two eyes that differ in their horizontal positions, giving the depth cue of horizontal disparity, also known as retinal disparity and as binocular disparity . Wheatstone showed that this was an effective depth cue by creating the illusion of depth from flat pictures that differed only in horizontal disparity. To display his pictures separately to the two eyes, Wheatstone invented

17854-399: The eyes, reversing the binocular disparity. Wheatstone (1838) found that observers could still appreciate the overall depth of a scene, consistent with the pictorial cues. The stereoscopic information went along with the overall depth. Computer stereo vision is a part of the field of computer vision . It is sometimes used in mobile robotics to detect obstacles. Example applications include

18012-499: The functional purpose of REM sleep is for procedural memory processing, and the rapid eye movement is only a side effect of the brain processing the eye-related procedural memory. Generally speaking, the body suspends homeostasis during paradoxical sleep. Heart rate , cardiac pressure, cardiac output , arterial pressure , and breathing rate quickly become irregular when the body moves into REM sleep. In general, respiratory reflexes such as response to hypoxia diminish. Overall,

18170-416: The hippocampus would be reinterpreted in relation to previous semantic representations or nodes." In the ultradian sleep cycle , an organism alternates between deep sleep (slow, large, synchronized brain waves) and paradoxical sleep (faster, desynchronized waves). Sleep happens in the context of the larger circadian rhythm , which influences sleepiness and physiological factors based on timekeepers within

18328-442: The image of an object over time with observer movement), though the impression of depth in these cases is often not as vivid as that obtained from binocular disparities. Therefore, the term stereopsis (or stereoscopic depth) can also refer specifically to the unique impression of depth associated with binocular vision (colloquially referred to as seeing "in 3D"). It has been suggested that the impression of "real" separation in depth

18486-710: The imaged scene. He named the phenomenon "shadow stereopsis". Shadows are therefore an important, stereoscopic cue for depth perception. He showed how effective the phenomenon is by taking two photographs of the Moon at different times, and therefore with different shadows, making the Moon to appear in 3D stereoscopically, despite the absence of any other stereoscopic cue. A stereoscope is a device by which each eye can be presented with different images, allowing stereopsis to be stimulated with two pictures, one for each eye. This has led to various crazes for stereopsis, usually prompted by new sorts of stereoscopes. In Victorian times it

18644-539: The intensity of REM sleep. These effects were the greatest during acute discontinuation compared to treatment and baseline days. However, the subjective intensity of dreaming increased and the proclivity to enter REM sleep was decreased during SSRI treatment compared to baseline and discontinuation days. After waking from REM sleep, the mind seems "hyperassociative"—more receptive to semantic priming effects. People awakened from REM have performed better on tasks like anagrams and creative problem solving. Sleep aids

18802-403: The ipsilateral (uncrossed) fibers of the temporal retina (nasal visual field). Layer one contains M cells, which correspond to the M ( magnocellular ) cells of the optic nerve of the opposite eye and are concerned with depth or motion. Layers four and six of the LGN also connect to the opposite eye, but to the P cells (color and edges) of the optic nerve. By contrast, layers two, three and five of

18960-554: The monoamine neurotransmitters which must be suppressed for REM sleep to occur. Administered at therapeutic doses, these drugs may stop REM sleep entirely for weeks or months. Withdrawal causes a REM rebound. Sleep deprivation stimulates hippocampal neurogenesis much as antidepressants do, but whether this effect is driven by REM sleep in particular is unknown. Although it manifests differently in different animals, REM sleep or something like it occurs in all land mammals —as well as in birds . The primary criteria used to identify REM are

19118-486: The need to re-examine the neurobiology of dreaming per se . Some researchers (Dement, Hobson, Jouvet, for example) tend to resist the idea of disconnecting dreaming from REM sleep. Previous research has shown that selective serotonin reuptake inhibitors (SSRIs) have an important effect on REM sleep neurobiology and dreaming. A study at Harvard Medical School in 2000 tested the effects of paroxetine and fluvoxamine on healthy young adult male and females for 31 days:

19276-405: The night and longer (~25 min) toward the end. Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM. The relative amount of REM sleep varies considerably with age. A newborn baby spends more than 80% of total sleep time in REM. REM sleep typically occupies 20–25% of total sleep in adult humans: about 90–120 minutes of

19434-508: The non-REM sleep improves the next-day recall of memorized pairs of words. Tucker et al. demonstrated that a daytime nap containing solely non-REM sleep enhances declarative memory —but not procedural memory . According to the sequential hypothesis , the two types of sleep work together to consolidate memory. Sleep researcher Jerome Siegel has observed that extreme REM deprivation does not significantly interfere with memory. One case study of an individual who had little or no REM sleep due to

19592-407: The optic chiasm, at the base of the hypothalamus of the brain. At this point, the information coming from both eyes is combined and then splits according to the visual field . The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain , respectively, to be processed. That is, the right side of primary visual cortex deals with the left half of

19750-492: The optic nerve fibers end in the lateral geniculate nucleus (LGN). Before the LGN forwards the pulses to V1 of the visual cortex (primary) it gauges the range of objects and tags every major object with a velocity tag. These tags predict object movement. The LGN also sends some fibers to V2 and V3. V1 performs edge-detection to understand spatial organization (initially, 40 milliseconds in, focusing on even small spatial and color changes. Then, 100 milliseconds in, upon receiving

19908-406: The organism which necessarily exceed the simple absence of a sleep phase. This method also stops working after about 3 days as the subjects (typically rats) lose their will to avoid the water. Another method involves computer monitoring of brain waves, complete with automatic mechanized shaking of the cage when the test animal drifts into REM sleep. Some researchers argue that the perpetuation of

20066-450: The patterns of communication between neurons in the retina. About 130 million photo-receptors absorb light, yet roughly 1.2 million axons of ganglion cells transmit information from the retina to the brain. The processing in the retina includes the formation of center-surround receptive fields of bipolar and ganglion cells in the retina, as well as convergence and divergence from photoreceptor to bipolar cell. In addition, other neurons in

20224-415: The periphery of the retina and are used to see at low levels of light. Each human eye contains 120 million rods. Cones are found primarily in the center (or fovea ) of the retina. There are three types of cones that differ in the wavelengths of light they absorb; they are usually called short or blue, middle or green, and long or red. Cones mediate day vision and can distinguish color and other features of

20382-460: The pons to prevent atonia have induced functional "REM behavior disorder" in animals. Rapid eye movement sleep (REM) has since its discovery been closely associated with dreaming . Waking up sleepers during a REM phase is a common experimental method for obtaining dream reports; 80% of neurotypical people can give some kind of dream report under these circumstances. Sleepers awakened from REM tend to give longer, more narrative descriptions of

20540-672: The population, it has repeatedly been shown to alleviate depression, albeit temporarily. More than half the individuals who experience this relief report it to be rendered ineffective after sleeping the following night. Thus, researchers have devised methods such as altering the sleep schedule for a span of days following a REM deprivation period and combining sleep-schedule alterations with pharmacotherapy to prolong this effect. Antidepressants (including selective serotonin reuptake inhibitors , tricyclics , and monoamine oxidase inhibitors ) and stimulants (such as amphetamine , methylphenidate and cocaine ) interfere with REM sleep by stimulating

20698-456: The presence of cyclodisparities of about 15 deg, and this has been interpreted as stereopsis with diplopia . Under normal circumstances, the depth specified by stereopsis agrees with other depth cues, such as motion parallax (when an observer moves while looking at one point in a scene, the fixation point , points nearer and farther than the fixation point appear to move against or with the movement, respectively, at velocities proportional to

20856-432: The preservation of certain types of memories : specifically, procedural memory , spatial memory , and emotional memory . In rats, REM sleep increases following intensive learning, especially several hours after, and sometimes for multiple nights. Experimental REM sleep deprivation has sometimes inhibited memory consolidation , especially regarding complex processes (e.g., how to escape from an elaborate maze). In humans,

21014-418: The process by which creativity forms associative elements into new combinations that are useful or meet some requirement. This occurs in REM sleep rather than in NREM sleep. Rather than being due to memory processes, this has been attributed to changes during REM sleep in cholinergic and noradrenergic neuromodulation . High levels of acetylcholine in the hippocampus suppress feedback from hippocampus to

21172-426: The propensity of the sleeper to dream vividly. The REM phase is also known as paradoxical sleep ( PS ) and sometimes desynchronized sleep or dreamy sleep , because of physiological similarities to waking states including rapid, low-voltage desynchronized brain waves . Electrical and chemical activity regulating this phase seem to originate in the brain stem , and is characterized most notably by an abundance of

21330-421: The proportion of REM sleep, as well as amount of total sleep. In other words, if at the end of a phase of deep sleep, the organism's thermal indicators fall outside of a certain range, it will not enter paradoxical sleep lest deregulation allow temperature to drift further from the desirable value. This mechanism can be 'fooled' by artificially warming the brain. REM atonia , an almost complete paralysis of

21488-500: The range of binocular fusion) and yielding only a vague impression of depth magnitude. Coarse stereopsis appears to be associated with the magno pathway which processes low spatial frequency disparities and motion, and fine stereopsis with the parvo pathway which processes high spatial frequency disparities. The coarse stereoscopic system seems to be able to provide residual binocular depth information in some individuals who lack fine stereopsis. Individuals have been found to integrate

21646-735: The relationship between muscle impulses during REM and associated mental imagery (which would also apply to people without the condition, except that commands to their muscles are suppressed). This is different from conventional sleepwalking , which takes place during slow-wave sleep, not REM. Narcolepsy , by contrast, seems to involve excessive and unwanted REM atonia: cataplexy and excessive daytime sleepiness while awake, hypnagogic hallucinations before entering slow-wave sleep, or sleep paralysis while waking. Other psychiatric disorders including depression have been linked to disproportionate REM sleep. Patients with suspected sleep disorders are typically evaluated by polysomnogram . Lesions of

21804-399: The retina, particularly horizontal and amacrine cells , transmit information laterally (from a neuron in one layer to an adjacent neuron in the same layer), resulting in more complex receptive fields that can be either indifferent to color and sensitive to motion or sensitive to color and indifferent to motion. The retina adapts to change in light through the use of the rods. In the dark,

21962-402: The right eye, making it a disparity detector. When a person stares at an object, the two eyes converge so that the object appears at the center of the retina in both eyes. Other objects around the main object appear shifted in relation to the main object. In the following example, whereas the main object (dolphin) remains in the center of the two images in the two eyes, the cube is shifted to

22120-441: The right in the left eye's image and is shifted to the left when in the right eye's image. Because each eye is in a different horizontal position, each has a slightly different perspective on a scene yielding different retinal images. Normally two images are not observed, but rather a single view of the scene, a phenomenon known as singleness of vision. Nevertheless, stereopsis is possible with double vision. This form of stereopsis

22278-407: The rods and cones of the retina . Retinal is the fundamental structure involved in the transduction of light into visual signals, i.e. nerve impulses in the ocular system of the central nervous system . In the presence of light, the retinal molecule changes configuration and as a result, a nerve impulse is generated. The information about the image via the eye is transmitted to the brain along

22436-427: The same overall intensity as in wakefulness. Electroencephalography during REM deep sleep reveals fast, low amplitude, desynchronized neural oscillation (brainwaves) that resemble the pattern seen during wakefulness, which differ from the slow δ (delta) waves pattern of NREM deep sleep. An important element of this contrast is the 3–10 Hz theta rhythm in the hippocampus and 40–60 Hz gamma waves in

22594-467: The shifted square. Nevertheless, when the two half images were viewed one to each eye, the square area was almost immediately visible by being closer or farther than the background. Julesz whimsically called the square a Cyclopean image after the mythical Cyclops who had only one eye. This was because it was as though we have a cyclopean eye inside our brains that can see cyclopean stimuli hidden to each of our actual eyes. Random-dot stereograms highlighted

22752-629: The species of the animal.) These secondary visual areas (collectively termed the extrastriate visual cortex) process a wide variety of visual primitives. Neurons in V1 and V2 respond selectively to bars of specific orientations, or combinations of bars. These are believed to support edge and corner detection. Similarly, basic information about color and motion is processed here. Heider, et al. (2002) found that neurons involving V1, V2, and V3 can detect stereoscopic illusory contours ; they found that stereoscopic stimuli subtending up to 8° can activate these neurons. As visual information passes forward through

22910-426: The thalamus. The lateral geniculate nucleus (LGN) is a sensory relay nucleus in the thalamus of the brain. The LGN consists of six layers in humans and other primates starting from catarrhines , including cercopithecidae and apes . Layers 1, 4, and 6 correspond to information from the contralateral (crossed) fibers of the nasal retina (temporal visual field); layers 2, 3, and 5 correspond to information from

23068-613: The translated LGN, V2, and V3 info, also begins focusing on global organization). V1 also creates a bottom-up saliency map to guide attention or gaze shift . V2 both forwards (direct and via pulvinar ) pulses to V1 and receives them. Pulvinar is responsible for saccade and visual attention. V2 serves much the same function as V1, however, it also handles illusory contours , determining depth by comparing left and right pulses (2D images), and foreground distinguishment. V2 connects to V1 - V5. V3 helps process ' global motion ' (direction and speed) of objects. V3 connects to V1 (weak), V2, and

23226-473: The two images are pulled apart slowly and symmetrically to a certain extent in the horizontal direction. In the vertical direction, there is a similar but smaller effect. This effect, first demonstrated on a random dot stereogram , was initially interpreted as an extension of Panum's fusional area . Later it was shown that the hysteresis effect reaches far beyond Panum's fusional area, and that stereoscopic depth can be perceived in random-line stereograms despite

23384-457: The two phenomena could be that the higher threshold for sensory interruption during REM sleep allows the brain to travel further along unrealistic and peculiar trains of thought. Some dreaming can take place during non-REM sleep. "Light sleepers" can experience dreaming during stage 2 non-REM sleep, whereas "deep sleepers", upon awakening in the same stage, are more likely to report "thinking" but not "dreaming". Certain scientific efforts to assess

23542-425: The uniquely bizarre nature of dreams experienced while asleep were forced to conclude that waking thought could be just as bizarre, especially in conditions of sensory deprivation . Because of non-REM dreaming, some sleep researchers have strenuously contested the importance of connecting dreaming to the REM sleep phase. The prospect that well-known neurological aspects of REM do not themselves cause dreaming suggests

23700-628: The various stimuli, for example stereoscopic cues and motion occlusion, in different ways. How the brain combines the different cues – including stereo, motion, vergence angle and monocular cues – for sensing motion in depth and 3D object position is an area of active research in vision science and neighboring disciplines. Not everyone has the same ability to see using stereopsis. One study shows that 97.3% are able to distinguish depth at horizontal disparities of 2.3 minutes of arc or smaller, and at least 80% could distinguish depth at horizontal differences of 30 seconds of arc . Stereopsis has

23858-429: The visual cortex. The optic radiations , one on each side of the brain, carry information from the thalamic lateral geniculate nucleus to layer 4 of the visual cortex . The P layer neurons of the LGN relay to V1 layer 4C β. The M layer neurons relay to V1 layer 4C α. The K layer neurons in the LGN relay to large neurons called blobs in layers 2 and 3 of V1. There is a direct correspondence from an angular position in

24016-406: The visual hierarchy, the complexity of the neural representations increases. Whereas a V1 neuron may respond selectively to a line segment of a particular orientation in a particular retinotopic location, neurons in the lateral occipital complex respond selectively to a complete object (e.g., a figure drawing), and neurons in the visual association cortex may respond selectively to human faces, or to

24174-513: The visual system is required for sensing, processing, and understanding the surrounding environment. Difficulty in sensing, processing and understanding light input has the potential to adversely impact an individual's ability to communicate, learn and effectively complete routine tasks on a daily basis. In children, early diagnosis and treatment of impaired visual system function is an important factor in ensuring that key social, academic and speech/language developmental milestones are met. Cataract

24332-406: The visual world at medium and high light levels. Cones are larger and much less numerous than rods (there are 6-7 million of them in each human eye). In the retina, the photoreceptors synapse directly onto bipolar cells , which in turn synapse onto ganglion cells of the outermost layer, which then conduct action potentials to the brain . A significant amount of visual processing arises from

24490-422: Was 481 nm. This shows that there are two pathways for vision in the retina – one based on classic photoreceptors (rods and cones) and the other, newly discovered, based on photo-receptive ganglion cells which act as rudimentary visual brightness detectors. The functioning of a camera is often compared with the workings of the eye, mostly since both focus light from external objects in the field of view onto

24648-407: Was called qualitative stereopsis by Kenneth Ogle. If the images are very different (such as by going cross-eyed, or by presenting different images in a stereoscope ) then one image at a time may be seen, a phenomenon known as binocular rivalry . There is a hysteresis effect associated with stereopsis. Once fusion and stereopsis have stabilized, fusion and stereopsis can be maintained even if

24806-442: Was seen in the previously referenced cataract and glaucoma studies, as well as in healthy children and adults. According to Pollock et al. (2010) stroke is the main cause of specific visual impairment, most frequently visual field loss ( homonymous hemianopia , a visual field defect). Nevertheless, evidence for the efficacy of cost-effective interventions aimed at these visual field defects is still inconsistent. Proper function of

24964-462: Was the prism stereoscope (allowing stereo photographs to be viewed), while in the 1920s it was red-green glasses (allowing stereo movies to be viewed). In 1939 the concept of the prism stereoscope was reworked into the technologically more complex View-Master , which remains in production today. In the 1950s polarizing glasses allowed stereopsis of coloured movies. In the 1990s Magic Eye pictures ( autostereograms ) – which did not require

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