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Query: UMLS:C0028738 (nystagmus)
 7,431 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Illusions of continuous body tilt and rotation can be elicited by vibrating postural muscles of subjects standing in the dark. During such illusory motion, the apparent pivot point of the body can be influenced systematically by touch and pressure cues. Strong apparent movement is sometimes accompained by nystagmus of compensatory sign. If a small target light is visible during vibration, visual motion of like direction and velocity will accompany the illusory body motion. We have designated this pattern of apparent body and visual motion the "propriogyral illusion". Full room illumination abolishes both components of the propiogyral illusion. When the propriogyral illusion is being experienced, there is a dissociation between apparent displacement and apparent velocity; the extent of displacement is always less than would be expected on the basis of apparent velocity. The illusions of continuous body motion and the propriogyral illusion represent elements of a general set of vibratory myesthetic illusions that influence apparent posture, sensory, localization, and position sense of the body. These illusions demonstrate an important contribution of muscle afferent and touch-pressure information to the central mechanisms that determine apparent spatial orientation and visual localization. They also provide evidence that somatosensory information about orientation can influence oculomotor control.
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PMID:Changes in apparent body orientation and sensory localization induced by vibration of postural muscles: vibratory myesthetic illusions. 46 54

A compelling illusion of body rotation and nystagmus can be induced when the horizontally extended arm of a stationary subject is passively rotated about a vertical axis in the shoulder joint. Lateral nystagmus with the fast phase beating in the opposite direction to the arm movement was found consistently; the mean slow phase velocity increased with increasing actual arm velocity and reached about 15 degrees/sec; the mean position of the eyes was deviated towards the fast phase as in optokinetic nystagmus, and the nystagmus continued after the cessation of stimulation (arthrokinetic after-nystagmus). The existence of an arthrokinetic circularvection and nystagmus indicates a convergence of vestibular and somatosensory afferents from joint receptors. It is concluded that information about joint movements plays an important role within the multisensory processes of self-motion perception.
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PMID:Arthrokinetic nystagmus and ego-motion sensation. 59 31

It has been demonstrated that the caloric test can be simplified further by making use of the oculogyral illusion. Since the test is conducted under conditions of optic fixation, this method probably also enhances the sensitivity of the caloric test. The reproducibility of the tests also appears high, at least in respect of measures of "canal paresis". When used in conjunction with other tests for detecting vestibular imbalance, e.g. examination for spontaneous and provocation nystagmus using Frenzel glasses, this OGI caloric test should provide a convenient procedure for the clinical examination of vestibular function.
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PMID:Caloric test with oculogyral illusion as response. 85 54

It can be shown that following an angular velocity step stimulus delivered in darkness, the nystagmic responses can be effectively 'dumped' after any interval in time by the application of an appropriate step decrement in velocity. In practise the null velocity is bracketed between those step decrements inducing just detectable nystagmus to left and right and can be determined within a range of +/- 1.5 degrees s-1. With test stimuli of 22, 44, and 64 degrees s-1 the 'dump' velocities have been established at varying intervals in time on four normal subjects. Contrary to expectations the dump velocity/time relations for all three test stimuli follow a convergent linear course. The dump velocities are unaffected by fixation suppression of the nystagmus induced by the test stimuli. The seeming irrelevance of nystagmus generation to dump velocity values is confirmed by the good correspondence with the results of a separate study using the oculogyral illusion as a guide in place of nystagmus. These findings are difficult to relate to conventional concepts of cupular dynamics.
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PMID:Observations bearing upon semi-circular canal dynamics. 270 35

In 8 healthy subjects we studied self-motion perception and nystagmus due to sinusoidal stimulation (amplitude 90 degrees peak to peak, frequency 0.05 Hz) of the horizontal semicircular canals, the cervical proprioceptors, and the retina. We used an electrically driven rotatory chair and optokinetic drum combination. For cervical stimulation the subject's head was placed in a clamp, attached to the drum. Eye movements were recorded by means of electrooculography, d.c. amplification. Subjects signalled the estimated head position by means of a 'joystick'. In the present series of experiments the vestibular and cervical informations were played off against each other in combined stimulation conditions with an interstimulus phase lag of 0 to 315 degrees, in steps of 45 degrees. Similarly, the vestibular and visual informations were played off against each other. Concerning estimated head position, our main finding is that both the visually and the cervically induced illusion of head rotation overrule the vestibular sensation of head motion. The ocular response to combined vestibular plus cervical stimulation shows that both nystagmus slow phases and saccades of the cervical and the vestibular responses add up by vectorial summation.
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PMID:Cervico-vestibular and visuo-vestibular interaction. Self-motion perception, nystagmus, and gaze shift. 698 18

Sigma-movement is an apparent movement seen when a stationary periodic visual pattern of the period PS is illuminated stroboscopically at the flash frequency fS and smooth gaze pursuit eye movements are performed across the pattern at an angular velocity Ve = PS X fS deg X S-1. Sigma-movement leads to an optokinetic nystagmus (Sigma OKN) which in turn sustains Sigma-movement perception. (1) Sigma-movement was also seen in an apparent three-dimensional periodic stripe pattern generated by two periodic monocular stimulus patterns with a certain degree of horizontal binocular disparity. (2) Sigma-movement perception and Sigma-OKN were also elicited by a stroboscopically illuminated, stationary, random dot stereostripe pattern. The periodicity PS of this pattern is generated on the cyclopean retina (Julesz 1971). The equation described above was also valid. When the time delay delta t between left eye and right eye flashes was varied, the apparent depth of the random dot stereostripe pattern decreased with increasing delta t, but the Sigma-effects were not affected. (3) Sigma-movement illusion and Sigma-pursuit movements can also be induced when real three-dimensional objects composed of periodic components are stroboscopically illuminated and adequate gaze or eye pursuit movements are induced. Sigma-movement is related to gaze movement and is therefore elicitable by eye, head or body movements. (4) Sigma-movement is presumably caused by the interaction of efference copy signals (generated in a cortical gaze pursuit system) and afferent visual signals. The present data indicate that neuronal mechanisms for this interaction are located--at least in part--at or beyond the level of binocular fusion and stereopsis.
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PMID:Sigma-movement and optokinetic nystagmus elicited by stroboscopically illuminated stereopatterns. 712 7

Dizziness is a nonspecific symptom caused by many different pathophysiologic mechanisms. Vertigo, an illusion of movement, indicates a lesion within the vestibular system. The duration of attacks and associated symptoms helps to determine the site of lesion and likely diagnosis. Examination of the dizzy patient should include a careful assessment of gait and balance and a search for spontaneous and positional nystagmus. The vestibulo-ocular reflex can be evaluated qualitatively at the bedside with the doll's eye, dynamic visual acuity, and ice water caloric tests. Each test provides different information about vestibular function.
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PMID:Approach to the evaluation of the dizzy patient. 857 Feb 43

Central nervous system (CNS) disorders and vestibulo-ocular reflex (VOR) degradation contribute to the loss of orientation and balance, typically causing the illusion of motion. VOR degradation may be caused by illnesses or common prescription medications, and this degradation may have serious repercussions in affecting one's ability to walk, maintain balance, or track moving objects. The two current VOR analysis techniques are applied to nystagmus signals (recordings of eye position during standardized tests) to isolate the two neuronal pathways used. These techniques are only partially successful because the VOR signal is passed through several filtering layers, to isolate the nystagmus signal, leaving it severely altered. In this paper, several alternate approaches are introduced: nonlinear robust ordering procedures, mathematical morphology, and wavelet filtering techniques are demonstrated. All approaches were as successful as the current techniques in isolating data from one neuronal pathway. Techniques for each of the three were also developed which would identify data from the second neuronal pathway as well. The nonlinear approach, which works using raw position data, bypasses layers of filtering. A robust technique is used to identify the points at which the data changes from that due to one neuronal pathway to the other, and the end result is obtained by concatenating the respective segments. The other two approaches work with velocity data obtained by differentiation, and because they are applied to non-original data, their results may be open to the possibility of error. Additionally, the two most recent approaches in the literature (using order statistic filters and fuzzy logic) have been implemented for a comparison of results.
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PMID:Nonlinear approaches for separation of slow and fast phase nystagmus signals. 794 58

Induced motion (IM) is the illusory movement of an object in the direction opposite to the real motion of adjacent detail. One theory of IM suggests that it results, in part, from suppression of optokinetic nystagmus (OKN) by fixational (smooth-pursuit) effort. In several studies an asymmetry in human vertical OKN has been reported, with upward optokinetic stimulation eliciting higher OKN gain than downward motion. This provides a test of the nystagmus-suppression theory of IM. If suppression of OKN contributes significantly to IM, upward inducing stimuli should result in a greater magnitude of the illusion than should downward stimulus motion. Additionally, the asymmetry of vertical OKN should become more pronounced at higher stimulus velocities. Therefore, the asymmetry of vertical IM should be greater at higher inducing-stimulus velocities. Twelve subjects viewed a large, random-dot stimulus, which moved either upward or downward at a velocity of 10, 40, or 70 deg s-1. Subjects fixated a horizontally moving laser spot and adjusted a rod to match the apparent slope of the motion path of the spot. IM magnitude was derived from these measures. Mean IM velocity was significantly higher with upward than with downward stimulation, and the difference was maximal at velocities of 40 and 70 deg s-1. The results are discussed within the context of the nystagmus-suppression theory and other theories of IM.
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PMID:Up-down asymmetry in vertical induced motion. 841 79

We studied the directional asymmetry of human vertical optokinetic nystagmus (OKN) and optokinetic after nystagmus (OKAN) based on two experiments conducted in 22 normal subjects. The results of the first experiment indicated that, during upward optokinetic stimulation OKN is produced by the pursuit system and the velocity storage system while during downward optokinetic stimulation the velocity storage system plays no significant role. Up-down asymmetry in vertical OKN seemed to be caused mainly by directional asymmetry of the velocity storage system. Furthermore, as the velocity storage function is very important for producing OKN at a higher stimulation velocity, domination of upward slow phase velocity becomes more apparent with a high stimulation velocity. In our second experiment the subjects were exposed to optokinetic stimulation with or without a stable fixation point. When subjects were exposed to optokinetic stimulation with fixation, they felt a rotating sensation within themselves or a moving sensation of the fixation point. When the stimulation disappeared, most experienced an illusion of small dots moving in the direction opposite the stimulation. In this condition some of the subjects showed after-nystagmus the slow phase of which was in the opposite direction. Subsequently the after-nystagmus became more distinct, with pursuit of the moving dot illusion. This result shows the existence of a mechanism which produces reverse after-nystagmus by mean of a retinal error input. We speculate that these phenomena play causative roles in reverse after-nystagmus (RAN), pursuit reverse after nystagmus (pRAN), and the RAN system.
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PMID:[Experimental study on directional asymmetry of vertical OKN and OKAN]. 883 Dec 31


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