PubMed Health⌕ Search

Biomedical subjects

J F Stein

Publications and source records attributed to J F Stein.

At least 91 records · Page 5Linked to original sources
PubMed1988

Planning of movement parameters in a visuo-motor tracking task.

Monkeys trained to track a continuously moving visual target with a joystick do so by making a series of intermittent positional corrections rather than in a single smooth movement. The amplitude of each correction is highly correlated both with the error between the target and joystick positions, and with the velocity of the target, measured at movement onset. This velocity estimate is used to predict where the target will be by the end of each movement, and thus helps to set its amplitude correctly. To do this successfully, the monkey must know in advance how long his next movement will take. But, confusingly, the eventual duration of each movement is also highly correlated with its amplitude. So it appears that the monkeys need to simultaneously know the amplitude and duration of a movement, but cannot determine one without prior knowledge of the other. We have examined two possible solutions to this problem; only one agrees with our data. The monkeys seem to select the amplitude of their movements by scaling target velocity by a standard time constant which gives the additional distance the target will move. They then add this to the positional error estimated at or near to the start of each movement, to get the final movement amplitude. The velocity scaling value that gives the best fit to the observed amplitudes is very close to the average duration of all the monkeys movements. We therefore propose that the monkeys use a standard time constant for the purpose of calculating how far the target will move during each of their positional corrections.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Disordered vergence control in dyslexic children.

By means of a synoptophore vergence eye movements were recorded in dyslexic and normal children while they were attempting to track small targets moving in simulated depth. Of the dyslexic children 64% were unable to make proper vergence movements when macular sized fusion targets (2 1/2 degrees) were employed, but their vergence control was better for larger (7 degrees) targets. The normal readers and the remaining dyslexics showed normal vergence responses for both large and small moving fusion stimuli. The results suggest that many dyslexics suffer a disorder of visuomotor control and perception for stimuli falling on the macula; this may explain their characteristic visual problems when reading. Hence recording vergence eye movement responses to small moving fusion stimuli may be useful in the investigation and treatment of children with reading difficulties.

Child↗
PubMed1987

Visuo-motor tracking during reversible inactivation of the cerebellum.

Two monkeys were trained to track a continuously moving target using a joystick. One then had a cooling probe implanted in nucleus interpositus of the cerebellum ipsilateral to his tracking arm. The other had a cannula implanted in the ipsilateral cortex of the lateral cerebellum through which local anaesthetic could be infused. Both monkeys showed similar tracking deficits during temporary inactivation of the cerebellum. The main effects seen were an increase in the peak velocity of their intermittent corrective tracking movements, and a decrease in the accuracy of these movements. Linear regression analyses were undertaken of the peak velocity and amplitude of each corrective movement against a number of possible control signals (target velocity, target position, error, error velocity etc.). The initially strong correlation of the amplitude of each movement made with target velocity was severely reduced during cerebellar inactivation, and movement amplitude became better predicted by the error between target and joystick positions. The peak velocity of movements became more strongly correlated with movement amplitude and less correlated with target velocity than in the intact animal. These results are consistent with the hypothesis that intermittent tracking is achieved by the production of 'primitive' movements, that are then adjusted to the correct amplitude and velocity required to catch up with the moving target. Our findings suggest that the cerebellum may normally be responsible for these adjustments, using visual and memorised cues about the target. The velocity of each movement may be reduced, and its amplitude adjusted, by combining measures of the current error with estimates of target speed and direction. We conclude that the cerebellum has an inhibitory role in tuning movements during visuo-motor tasks and that optimal tuning using feedforward measurements of target motion cannot be made without it.

Anesthesia, Local↗
PubMed1987

Fine binocular control in dyslexic children.

Dyslexic children often complain that letters seem to move around. The hypothesis advanced here is that this is a symptom of immature vergence control which leads to an unstable sense of visual direction. Evidence is presented that (1) sixty-seven per cent of dyslexic children exhibit poor dynamic control of vergence movements in response to a small fusion stimulus, (2) most good readers have good vergence control, (3) children with poor vergence control have reduced stereoacuity, (4) six months monocular occlusion for reading and close work assisted 51 per cent of dyslexics with unstable vergence control to improve; thereafter their reading improved rapidly also. It is concluded that defective vergence control is an important, though not the only, cause of dyslexics' problems.

Child↗
PubMed1987

Cerebellar neuronal activity related to arm movements in trained rhesus monkeys.

1. The role of the paravermal cerebellum in controlling arm movements in monkeys trained to perform visually guided movements was investigated. Discharge patterns of extracellularly recorded Purkinje, Golgi, nuclear and unidentified cells were correlated with arm position, velocity and acceleration. 2. The discharge of thirty-seven out of fifty-two movement-related Purkinje cells and that of thirty-three out of forty-five other movement-related cerebellar neurones was more highly correlated with limb velocity (0.95 greater than r greater than 0.4) than with position or acceleration. Twelve out of fifty-two Purkinje cells and twelve out of forty-five other cells were related to both limb velocity and limb position. Three Purkinje cells were related to limb acceleration and position and no cell was related to position or acceleration alone. 3. Modulation of discharge of these cells usually preceded movement (range -240 ms, unit leading movement, to +180 ms, unit lagging; mode -36 ms; mean -15 ms). 4. Each movement-related neurone was tested for four directions of movement. All showed a preferred direction in which the correlation with arm movement velocity was highest. However, 43% (30/70) correlated at r greater than 0.4 with movements in a second direction, usually that opposite to their preferred direction. Sixty-three per cent of these neurones fired earlier during movements in the preferred than in the opposite direction. 5. It is concluded that the paravermal cerebellum may be involved in computing the velocity vectors required for achieving properly directed and co-ordinated movements of the whole arm.

Action Potentials↗
PubMed1986

Manual tracking of visual targets by trained monkeys.

Monkeys were trained to track moving visual targets using a hand-held joystick. The overall frequency response of their visuomotor system was determined using sinusoidal target waveforms. Their responses could be approximately represented by a linear feedforward model consisting of a 0.9 Hz low-pass filter with an additional 150 ms time delay. However, the monkeys normally tracked the target by making intermittent movements of the joystick. Thus, their responses were more realistically modelled as a non-linear sampled feedback model with a loop delay of 250-280 ms. Intermittency allows the monkeys to achieve a good frequency response and maintain tracking stability despite an irreducible visuomotor loop delay of 250-300 ms. When tracking pseudorandom waveforms the monkeys' movements were mainly controlled by positional error. But when tracking predictable sinusoids the amplitude and velocity of each movement was not solely determined by positional error. Instead the monkeys made use of target feedforward, and also internal models of the target waveform, in order to improve their tracking performance. Feedforward control dominated feedback control at high target frequencies, suggesting that the monkeys cannot model targets with long cycle periods.

Animals↗
PubMed1986

The Dunlop test and reading in primary school children.

Using the Dunlop synoptophore test we have examined the reliability of vergence control for small fusion targets in 753 primary school children aged 7-11, and we have compared these results with the reading performance of 451 of them. 30% of the total sample of children had unstable responses in the Dunlop test. The proportion decreased with age, ranging from 49% of 5-year-olds to only 11% of 10-year-olds. The reading of children who had developed accurate vergence control was on average 6.3 months in advance of those who had not. Those with unstable Dunlop test responses were much more likely to be backward or low normal readers than children with stable responses. We conclude that in experienced hands the Dunlop test is a useful indicator of the development of vergence control and that immaturity of vergence control may contribute to children's reading problems.

Aging↗
PubMed1985

Visuomotor tracking with delayed visual feedback.

A rhesus monkey and five human subjects used a hand-held joystick to track unpredictable continuously moving targets. Both monkey and human respond by making discrete ("step-and-hold") corrections of positional error, at an average frequency of 1.33 and 2.26 movements/second, respectively. By delaying visual feedback of joystick position, we could reduce these frequencies in a predictable manner. These results imply that the primate visuomotor system probably does not operate as a "sampled-data mechanism" governed by an asynchronous clock, but that inevitable delays in visuomotor feedback control determine the frequency of corrective movements.

Animals↗
PubMed1984

Ipsiversive rotation in awake rats following chronic electrical stimulation of one caudate nucleus.

Rats were chronically implanted with stimulating electrodes in one caudate nucleus. Under light anaesthesia they received daily electrical stimulation (100-400 microA/HZ) for 30 min on 4 consecutive days. During this period, and for up to 3 subsequent days, tests for possible circling behaviour in response to administration of apomorphine i.p. were performed daily. Turning occurred towards the treated side and was reversible. The possibility is discussed that high levels of dopamine are released into the striatum during electrical stimulation, inducing transient subsensitivity of striatal dopamine receptors.

Animals↗
PubMed1984

Time series analysis of neuronal signals recorded in the cerebellum of trained monkeys.

Recordings from cerebellar neurones have been made in monkeys trained to track a target moving sinusoidally at 0.33 Hz. The neuronal point even time series was first low pass filtered at 0.33 Hz to compare with the target and monkey movements. Short lengths of data were then subjected to Fourier and autoregressive spectral analysis in order to characterize higher frequencies in the neuronal signal. Stable components were identified at around 0.33 Hz (when the monkey was tracking well), 1.0 Hz and 8.5 Hz. The variation of many of the intermediate frequencies was suggestive of entrainment interactions between the basic components. The power at 1.0 Hz may result from the operation of a visuomoter control loop, whilst 8.5 Hz may characterize proprioceptive control.

Action Potentials↗
PubMed1982

Diagnosis of dyslexia by means of a new indicator of eye dominance.

Many dyslexic children are unable accurately to control the movements of their eyes even when they are not trying to read. This immaturity helps to explain their visual confusions. It may result from failure to develop dependable associations between retinal and ocular motor signals these are essential to fix the true, as opposed to retinotopic, locations of objects in the outside world. We have used a new test to study retinal/ocular motor correspondence in dyslexic children and age/IQ matched normal readers. Over half the dyslexics showed unstable ocular motor dominance.

Child↗