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Biomedical subjects

S Ron

Publications and source records attributed to S Ron.

35 records · Page 2Linked to original sources
PubMed1989

Saccadic tracking of a periodic target motion in the cat.

Cats were tested for their ability to follow a dot target which periodically jumps horizontally from side to side. They can learn to perform saccadic tracking of various stimulus frequencies, and often they produce saccades predicting the target displacements. The preferred stimulus frequency for response to synchronize was in the 0.5-Hz range. Cats tend to undershoot the target. They also tend to adopt a strategy of locking predominantly to one direction of displacement, but they can be trained to reverse this preferred side or to lock to both sides. Saccades to the preferred side are more accurate, and longer and slower in comparison to saccades to the other side, thus demonstrating a velocity-accuracy trade-off phenomenon in the cat responses. Saccadic characteristics as expressed by the main sequence are apparently a stable property independent of the stimulus frequency.

Acceleration↗
PubMed1989

Temporal characteristics of tapping responses in healthy subjects and in patients who sustained cerebrovascular accident.

Tapping responses were recorded in a group of patients who sustained lesions from cerebrovascular accidents and from an age-matched group of healthy subjects. In each experiment the stimuli were an auditory signal, a flash, or a light touch on the arm, delivered either at random intervals or at fixed time intervals of 1, 2, 3, or 4 s. The tapping response was done with each hand separately (first experiment) or with each hand alternately (second experiment). Healthy subjects, 'predicted' the stimuli (response time less than 150 ms), when the 'preferred' fixed time interval was used. One group of patients (n = 3), did not predict the stimuli at the preferred fixed intervals when tapping was done with the hand related to the involved hemisphere. The second group of patients (n = 3) did not predict the stimuli when tapping was done with either hand.

Aged↗
PubMed1989

Applying a model of saccadic prediction to patients' saccadic eye movements.

A mathematical model of eye tracking of periodic square wave target motion has previously been proposed. In this work the model was further studied with regard to saccadic response time to symmetrical square wave target motion in 6 patients with unilateral parietal lesions following cerebrovascular accidents. Three types of saccadic response time were noted. In patients with type I, saccades contralateral to the damaged hemisphere had similar characteristics to those found in ipsilateral direction, but with longer response time. In those with type II, the saccadic response time was about the same on movement in either direction for repetitive target cycle durations of 1.2 or 2.0 s. In patients with type III, the target motion could not be predicted, in either direction.

Aged↗
PubMed1985

[Focal nodular hyperplasia--mixed liver cell and bile duct adenoma].

Although benign tumorous lesions of the liver are rare, they can be found particularly among women in the preclimacteric age group. Usually, the clinical findings are non-characteristic. Differentiation from other space-occupying growths can be difficult due to the variable appearance of focal nodular hyperplasia. The selective angiogram is typical in some cases and no further radiological procedures are required. Nevertheless, histological examinations should be performed for complete clarification.

Adenoma, Bile Duct↗
PubMed1985

Ocular congenital fibrosis syndrome.

The symptomatology of congenital fibrosis of extraocular muscles, markedly restricted eye movements, blepharoptosis and chin elevation were found in 10 individuals and three generations of one family. The mode of inheritance is compatible with a variable expressive dominant trait. Our experience with the surgical management of the condition using more aggressive procedures than currently employed is described.

Adolescent↗
PubMed1980

Time-related changes in the distribution of sleep stages in brain injured patients.

The correlation between sleep pattern and cognition was studied in a follow-up of 9 patients with traumatic brain injury. The follow-up extended for a mean of 38 weeks after regaining consciousness, with 4-7 study periods for each patient. In addition to sleep pattern, 3 other variables were evaluated: independence in activities of daily living, locomotor and cognitive functions. In 7 patients there was a high correlation (r greater than 0.89) between cognition and REM sleep improvement whereas in 2 patients the correlation was lower (r less than 0.6). It is suggested that in the first group the REM mechanism was intact whereas in the latter, where a brain stem lesion was present, the REM mechanism was damaged. It is also suggested that the sleep pattern recovery time constant depends on the insult to the sleep mechanism structure whereas the REM steady-state recovery process depends on both cognitive maximal capacity and REM neural mechanism integrity.

Adolescent↗
PubMed1978

Ocular saccades in Duane's syndrome.

Since Hering's law might be affected when paradoxical innervation exists, 10 patients with Duane's syndrome were studied. Eye movements were measured by binocular recording of electro-oculogram. Our study shows clearly that the sound eye's motility is also affected. When adduction of the affected eye is present, Hering's law holds, whereas when adduction is limited this law cannot be demonstrated.

Adolescent↗
PubMed1978

Eye movements in brain damaged patients.

Saccades, smooth movements and vergence were recorded in 28 patients with brain lesions using an infrared scleral reflexion technique. Large impairment in eye movement responses under visual feedback were recorded from the majority of the patients. The implication of these deficiencies on the vocational rehabilitation of the patients is discussed.

Brain Damage, Chronic↗
PubMed1977

Cerebellar role in smooth pursuit movement.

It is generally believed that pursuit eye movements are unaffected by cerebellar cortical atrophy or cerebellectomy. The present study was performed on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial injury or cerebellar tumors. Eye movements were measured by DC electro-oculography. A clear disparity of the slow phase of the optokinetic nystagmus was observed. When eye movements were contralateral to the ablated side the slow phase of optokinetic nystagmus was statistically slower than drum or visual field velocity. It is suggested that the cerebellum network is involved in the mechanisms of the smooth pursuit movement.

Brain↗
PubMed1977

The cerebellum involvement in the generation of saccades.

It was assumed that the cerebellum is not essential for eye movements, playing only a modifying and influencing role. Recently it has been shown that the directions of the saccades can be related to a stimulated cerebellar site. This study was done on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial or cerebellar tumors. The results further indicate that lack that lack of some cerebellar neural structure affects the nature of the saccade: it does not move the eyes in one saccade to acquire the new target and its amplitude duration relationship changes. It is suggested that cerebellar cortex generates a neural pulse based on teleceptive information about stimulus location with respect to an observer's head, corrects this information for initial eye position and sends out a signal to the saccadic pulse generators which move the eyes to acquire the new target.

Brain↗
PubMedDate not supplied

Contrast sensitivity and the near point of accommodation after work with a visual display unit.

After several hours of work with a visual display unit (VDU), operators become myopic for a short time. Such transient myopia may be evaluated by measuring contrast sensitivity to a modulated grating pattern. The aim of the present study was to determine whether there are any accumulative myopic effects after 1 day of VDU work. We examined grating contrast sensitivity in a group of 13 full-time workers and in 13 office employees who used VDUs only sporadically. The results, which were compared with the near point of accommodation, clearly illustrated that there is no decrease in contrast sensitivity. In the VDU group the decrease in the near point of accommodation was uniformly distributed between zero and 1.0 diopter, whereas among the non-VDU workers 77% of the decrease was between zero and 0.25 diopter. We conclude that the myopic changes in the refractive status of operators after VDU work are not evident in a decrease in contrast sensitivity. However, in VDU workers the dynamic range of accommodation was smaller, suggesting that the visual fatigue and visual stress that developed at work hindered visual activities after work.

Accommodation, Ocular↗
PubMedDate not supplied

Training in oculomotor tracking: occupational health aspects.

Smooth pursuit and optokinetic nystagmus were repeatedly examined in nine patients who sustained hemilateral brain injury. The follow-up period extended over several months of the in-hospital rehabilitation phase. Five of the patients were trained for 3-10 weeks to improve tracking responses using a biofeedback technique; the remaining four patients were not trained and served as a control group. In all patients in the first group gain responses improved and the recovery time constant increased at a rate higher than that in the untrained group. We suggest that our training procedure can be extended to other types of patients with impaired smooth pursuit tracking and may also benefit workers in need of good tracking performance.

Biofeedback, Psychology↗
PubMedDate not supplied

Model of coupled or dissociated eye-head coordination.

Tight coupling between eye and head movements have been observed in response to a single visual target offset or a single flash. On this basis, when the visual stimulus consists of two successive steps or flashes in the same (horizontal) direction, either increasing in eccentricity or decreasing in eccentricity, gaze should be due to concomitant eye and head angular displacement. The main findings were that in response to increasing eccentricity stimulus, the majority of the gaze movement had a staircase pattern, and to decreasing eccentricity stimulus, a pulse-step pattern. Some responses were one gaze movement to the final target (or flash) offset. In all these responses, eye and head were tightly coupled. In some cases, however, in response to two flashes or two successive steps decreasing in eccentricity, the initial eye and head movements were dissociated: eye and head were directed to different offsets. Current eye-head models assume a strong coupling between the head displacement and the eye saccade. We have modified the Laurutis and Robinson model to accommodate the new findings of saccade-VOR cooperation and eye-head dissociated responses. we suggest that when gaze falls short of the target offset, the retinal error signal is not only fed to the saccadic system but also partially suppresses the VOR gain control. This allows for "corrective VOR" movements after the gaze saccade has occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗