Binocular amblyopia improved by yellow spectacles.
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Amblyopia↗
Biomedical subjects
J F Stein
Publications and source records attributed to J F Stein.
Covert orienting to central visual cues and sport practice relations in the development of visual attention.
This study examines the development of controlled covert orienting of visual attention, according to the age and the level of performance of tennis players. Practicers and nonpracticers age 13, 16, and 25 participated in a covert orienting task. On each trial, subjects responded to a target which appeared in one of four locations arrayed horizontally across the display. Three central cues were used: neutral, the cue did not specify in which location the target would appear; valid, the target was present in the cued location on 80% of the trials; invalid, the target was present in one of the uncued locations on the remaining 20% of the trials. The results showed that (1) practicers were not faster than nonpracticers in processing the signals, (2) observers of all ages oriented attention voluntarily to the cued locations, (3) central cues had a smaller effect on older and practiced subjects, and (4) developmental and sport practice factors had similar effects on orienting efficiency. The implications of these findings for theories of attentional development are discussed.
Adolescent↗
Does attention modulate the perception of luminance changes?
In a previous study assessing the modulation of visual processing by attention, Bonnel, Possamî, and Schmitt showed that, when discriminating line-length, subjects precisely shared processing resources between two pairs of lines presented to the left and right of fixation. In a close replication requiring the detection of luminance increments instead of line-length differences, subjects were unable to follow the instructions and to allocate attention differentially, thus supporting the claim that light detection is fundamentally different from shape discrimination. In a subsequent experiment, we tested and rejected the possibility that luminance perception was not open to modulation by attention due to its physical nature. Replacing brightness detection by brightness identification allowed voluntary control on the quality of processing to be evidenced. The similarity between the latter results and the data from line-length discrimination suggests that task requirements may be crucial in determining the distribution of attention.
Attention↗
Effect of potassium on ventilation in the rhesus monkey.
Increasing the concentration of arterial plasma K+ to 6-8 mM increased ventilation in two sedated analgesic-treated rhesus monkeys who had their end-tidal CO2 held constant during euoxia (arterial oxygen pressure, Pa,O2, ca 100 Torr) and hypoxia (Pa,O2, ca 40 Torr). During euoxia and hypoxia, hyperkalaemia increased ventilation up to 40 and 250%, respectively. This effect was reduced in euoxia and virtually abolished in hypoxia following an abrupt switch to 100% oxygen. Thus the ventilatory response of this primate to hyperkalaemia is at least as sensitive as that of the cat and if hypoxia is added the two stimuli generate a powerful drive to breathing.
Animals↗
Role of the cerebellum in visual guidance of movement.
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Animals↗
Yellow spectacles to improve vision in children with binocular amblyopia.
Yellow spectacles were given to 20 children who had binocular amblyopia. Immediately, their vision improved. Furthermore, in the younger children, after they had worn the yellow lenses for up to nine months, this improvement persisted even when they were not wearing the spectacles. Yellow filters may help these children with binocular amblyopia because they remove the blue fringes that are due to chromatic aberration of the eye.
Adolescent↗
Specialization of the right hemisphere for visuomotor control.
The accuracy of saccades directed towards the remembered positions of targets in left (LVF) or right (RVF) visual hemifield was measured. The majority of right-handed subjects were found to be more accurate at directing their gaze to locations in the LVF than in the RVF, suggesting that the right hemisphere is superior to the left in oculomotor control. Even after completion of a corrective saccade following the primary saccade, subjects systematically undershot target direction and overshot target depth, suggesting that visual feedback normally plays an important role in the fine guidance of gaze after the completion of a primary saccade.
Adult↗
Neuronal activity in the lateral cerebellum of trained monkeys, related to visual stimuli or to eye movements.
1. The responses of neurones in the lateral cerebellar cortex to visual stimuli and to eye movements were recorded in rhesus monkeys trained to perform visually guided arm and eye movements in a tracking task. 2. Twenty-two of 134 units recorded (16%) modulated their discharge in response to a bright Xenon flash. They were mainly located in the dorsal paraflocculus. Among those identified as Purkinje cells both simple spike and climbing fibre responses to the flash were seen. (72% of the units were related to arm movements; these were centred in the paramedian lobule, and have been described fully in Marple-Horvat & Stein (1987).) 3. The visual responsiveness of one of the units varied according to the phase of the monkey's task. Around the time that the target stepped, which was the monkey's cue to move, its sensitivity to other stimuli disappeared. 4. Only two neurones responded to the movements of the tracking target. These responses were conditional upon the monkey using visual signals to guide his movements; they did not respond to the target step if he moved before the target did. 5. Fourteen units (10%) located in crus I and II and lobulus simplex correlated strongly with the velocity of horizontal eye movements. Only one of these also responded to visual stimuli. 6. Thus most neurones were found to carry only visual, or eye movement, or limb movement information rather than combinations of these signals; they were located in different but overlapping regions of lateral cerebellar cortex. Visually responsive neurones are probably involved in planning the visual goal of movements, while eye and arm movement neurones probably help to create co-ordinative structures for executing voluntary eye and arm movements.
Action Potentials↗
Spatial discrimination in children with poor vergence control.
In a 1987 study of children with reading difficulties, Stein, Riddell, and Fowler observed a relationship between poor vergence control, as indicated on a synoptophore vergence test, and the children's problems with learning to read. They suggested that poor vergence control led to impaired accuracy of spatial localisation and that this impeded learning to read. Here we have compared the accuracy of spatial localisation on a nonlinguistic computer game by children having good and poor vergence control. The children with poor vergence control made significantly more errors when locating targets than children with good vergence control. These results lend further support to the hypothesis that some children do not learn to read because they are unable to determine accurately the positions of letters in words.
Attention↗
Representation of egocentric space in the posterior parietal cortex.
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Animals↗
Unfixed reference, monocular occlusion, and developmental dyslexia--a critique.
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Child↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗