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Biomedical subjects

J E Raymond

Publications and source records attributed to J E Raymond.

31 records · Page 2Linked to original sources
PubMed1988

Fixational instability and saccadic eye movements of dyslexic children with subtle cerebellar dysfunction.

Fixational stability and saccadic eye movements were measured in 9- to 13-year-old dyslexics with signs of subtle cerebellar dysfunction and in a group of age-matched normal readers. This group of dyslexics was specifically chosen because cerebellar disorders are often associated with ocular motor dysfunction. Dyslexic children were found to exhibit significantly greater fixational instability than controls while viewing a simple, stationary stimulus. Although both groups of children showed disruption of fixational stability when viewing stationary targets against optokinetic backgrounds, gaze stability of dyslexics was more degraded than that of controls. However, latency and accuracy of saccadic eye movements of dyslexic children were not different from those of normal readers. The results suggest that poor maintenance of gaze stability, rather than inadequate control over saccadic eye movements, characterizes the ocular motor problems that may contribute to reading difficulties in this subgroup of dyslexics.

Cerebellar Diseases↗
PubMed1988

Usefulness of computerized visual acuity testing in a pediatric ophthalmology clinic.

We investigated the usefulness of a computerized illiterate-E-style acuity test in 111 children ranging in age from 3 to 13 (mean 6.56) years consecutively referred to a large pediatric ophthalmology clinic. Visual acuity was measured in both eyes of each subject by means of conventional testing with an optical projection device and computerized testing with a program run on a microcomputer. Of the 222 eyes 155 (70%) showed no difference in visual acuity between the two procedures. A difference of one acuity line was found for 63 eyes (28%), and a difference of two lines was found for 4 eyes (2%). The conventional test yielded a higher acuity score in 75% of the cases in which a one-line difference was found and 50% of those in which a two-line difference was found. Our results indicate that computerized testing is a valid and effective method of assessing visual acuity in children.

Adolescent↗
PubMed1988

The failure of antimotion sickness medication to improve reading in developmental dyslexia: results of a randomized trial.

Although there have been no randomized clinical trials of the efficacy of antimotion sickness medication treatment of developmental dyslexia, some children are treated in this way. We have performed two evaluations of such treatments. In Experiment 1, 12 children participated in a double-blind within-subject crossover design to test the acute (2-day) administration of four preparations: 10 mg methylphenidate, 12.5 mg meclizine, both methylphenidate and meclizine, or placebo. Improvements obtained with each drug were scattered across measures of reading fluency, balance and coordination, and eye movements, suggesting that a chronic trial would be justified. In Experiment 2, six children from Experiment 1 received 12.5 mg meclizine b.i.d. for 3 months and placebo for 3 months in a double-blind within-subject crossover design. Meclizine had no effect on reading, but it significantly improved ocular motor stability during steady fixation. This study thus failed to support the hypothesis that meclizine is of benefit in developmental dyslexia.

Child↗
PubMed1985

Viewing distance and the sustained detection of high spatial frequency gratings.

Although conventional visual acuity tests measure the ability to resolve fine detail, many visual tasks demand prolonged detection. By evaluating the ability to maintain visual resolution, we observed that detection of stimuli subtending a small but constant visual angle depends on viewing distance and is probably determined by accommodative control. Detection was longest when viewing distance corresponded to the individual observer's accommodative resting, or tonus, position and fell off markedly for further distances. Since most visual assessment procedures involve a momentary detection criterion, they will not predict the ability to sustain accommodation and may thus overestimate visual resolution for prolonged viewing tasks.

Accommodation, Ocular↗
PubMed1985

Reduction of body sway by stimuli imaged within a cortical scotoma: a case study.

The reduction of body sway by visual stimulation was equally effective for stimuli imaged within a cortical scotoma or in the mirror image position in the normal visual field. The results are consistent with the concept of distinct visual orientation and discrimination modes of processing visual information, which suggests that spatial orientation functions do not necessarily involve awareness.

Adult↗
PubMed1984

The effect of contrast on sustained detection.

During a 1 min observation, the percentage of time a high spatial frequency grating can be detected is influenced by the contrast and spatial frequency of a second, superimposed and orthogonally-oriented sine wave grating. Increasing contrast of the second pattern aids detection of the first by providing a more effective accommodative stimulus. The function relating spatial frequency and the minimum contrast needed to activate accommodation is similar in shape to the classical contrast sensitivity function. However, an order of magnitude more contrast is required to stabilize accommodation than is required to simply detect a pattern. These results suggest that performance on visual tasks requiring sustained rather than brief detection may be markedly impaired under low contrast conditions.

Accommodation, Ocular↗
PubMedDate not supplied

Movement direction analysers: independence and bandwidth.

Opponent, or ratio, models of movement direction perception propose that pairs of analysers, sensitive to opposite directions, are linked in an opponent fashion. Alternatively, distribution models posit independence of movement direction analysers. To investigate analyser independence, a direction-selective adaptation experiment was conducted in which motion coherence thresholds for random-dot apparent motion stimuli were measured for upward, downward, leftward and rightward motion with and without prior adaptation to rightward motion. Coherence thresholds for rightward motion were elevated on average by 0.64 log units after adaptation. Thresholds for motion in the other directions remained unchanged. Since opponent models predict enhanced sensitivity after adaptation for the direction opposite that of adaptation, these results suggest that movement direction analysers operate independently. In a second experiment subjects adapted to a bidirectional stimulus containing an equal number of leftward and rightward moving dots. Leftward and rightward coherence thresholds were elevated even though no motion aftereffects were produced. A third experiment in which coherence thresholds for test directions within a narrow range were measured with and without prior adaptation to motion in the direction of the range's mean showed that threshold elevation was maximal when test and adaptation direction were matched and fell off as the difference in adaptation and test direction increased. The resulting functions indicate that the bandwidth of movement direction analysers is between +/- 35 and +/- 40 deg, a value consistent with reported mean directional tuning functions of movement sensitive units in the middle temporal area but smaller than previously reported psychophysical values.

Adaptation, Ocular↗