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Biomedical subjects

J Turkel

Publications and source records attributed to J Turkel.

8 recordsLinked to original sources
PubMed1984

Characteristics of saccades in human infants.

Infants (14-151 days) and adults were shown two-dimensional geometric forms or stimuli from a set of highly textured patterns. Their eye movements were recorded by an infrared corneal reflection eye movement recorder as they freely scanned the stimuli. For both infants and adults, linear relationships were found between the peak velocities of fast eye movements and their amplitudes (main sequences). Infants viewing texture stimuli had main sequences with slopes comparable to those of adults. Infants viewing simple geometric forms made slower saccades. They also showed more eye movement oscillations which analyses showed were probably back-to-back saccades. Both the slower saccades and saccadic oscillations were attributed to factors related to the attentional value of the stimuli.

Adolescent↗
PubMed1984

Orientational asymmetries in small-field optokinetic nystagmus in human infants.

Optokinetic nystagmus (OKN) is a pattern of reflexive eye movements which occurs when portions of the visual field are in continuous motion. Gratings moving at 7 deg/s either horizontally (left or right) or vertically (up or down) were presented on a viewing screen subtending 30 degrees by 22 degrees. Horizontal (HOKN) and vertical (VOKN) OKN were recorded under binocular viewing conditions from infants and adults. Eye movements were recorded by means of an infrared corneal reflection eye movement recorder. OKN to horizontal and vertical stimuli was different in pattern for infants. Infants' HOKN was of significantly higher frequency and lower amplitude than their VOKN. Infants below 4 months of age also showed an asymmetry within VOKN between upward and downward stimulus motion, with markedly lower gains and more variable slow phase following movements for downward moving stimuli. No differences were found in HOKN to the right and left. There was also no evidence of a build-up of slow phase velocity over time. Infants' fast phases showed peak velocity/amplitude relationships like those of adults, and like those of infant saccades recorded in a previous study of infants' fast eye movements. Across all directions of stimulus movement, infants had lower slow phase gains and OKN frequencies, and larger slow phase amplitudes than adults. The characteristics of infants' OKN are discussed in relation to those observed in other species and in adult clinical patients with eye movement disorders.

Adolescent↗
PubMed1984

Rocket-ship psychophysics. Assessing visual functioning in young children.

A set of psychophysical procedures is described for rapidly measuring visual functions such as spatial contrast sensitivity, flicker fusion, and rod and cone two-color increment thresholds in young children. The psychophysical procedures, disguised as electronic space games, use a forced-choice paradigm combined with the method of descending limits. Because children enjoy the tasks and are highly motivated, the tests yield good sensory thresholds in a short period of time. However, when thresholds from 6-8-year-old children are compared with those of adults, the children have slightly higher thresholds for all of the functions tested. The differences are ascribed to the tendency of children to adopt a guessing strategy when stimuli are close to threshold.

Adolescent↗
PubMed1981

Termination of very early pregnancy by vaginal suppositories-(15S)-15-methyl prostaglandin F2 alpha methyl ester.

A new approach to terminate very early pregnancy was tried on 49 healthy women who were proven to be pregnant from 31 to 47 days from their last menstrual period. All pregnancies were confirmed either by UCG or serum HCG-B subunit. (15S)-15-Methyl PGF2 alpha Methyl Ester in a suppository form was administered in two separate doses: 1.0 mg initial dose followed by 3.0 mg one hour later. Patients were kept under observation for 8 hours. Blood sampling for progesterone, HCG-B, and prostaglandin levels were assayed at 0 degree, 30', 1 degree, 4 degrees, 8 degrees and 14 days. Patients were re-examined at a two week follow-up visit. Pelvic examination and pregnancy tests were performed to confirm whether the pregnancy was successfully terminated. There were no significant changes in serums progesterone and HCG-B levels during the 8-hour observation period. Both levels declined significantly to very low levels at 14 days post-therapy, confirming the clinical impression of successful termination of pregnancy. Plasma prostaglandin levels rose as early as 30 minutes after initiation of therapy, peaked at 4 hours and declined gradually afterwards. Most side effects such as nausea, vomiting, diarrhea and cramps, although clinically manageable, were still bothersome. One patient experienced an episode of vasovagal syncope. The majority of patients required medical observation up to 6 hours. Clinical implications of this new approach of termination of very early pregnancy are discussed.

Abortion, Induced↗
PubMed1979

Mapping the representation of the visual field by electrical stimulation of human visual cortex.

Electrical stimulation of human visual cortex produces punctuate phosphenes in the visual field. This phenomenon, which is being explored as the basis for a visual prosthesis for the blind, also provides the first electrophysiological information about the retinocortical map in man. Stimulation of points clustered on the surface of the visual cortex produces phosphenes clustered in visual space. However, adjacent surface electrodes located on opposite sides of a sulcus can produce widely separated phosphenes, because the intervening cortex is buried and inaccessible to stimulation. Such electrodes can also produce multiple phosphenes by simultaneously stimulating both banks of the sulcus. Electrodes which are widely spaced on the brain can produce phosphenes close together in visual space providing they stimulate cortex corresponding to overlapping maps in areas 17 and 18. Analysis of the phosphene map indicates that successive stimulation of points further from the tip of the occipital pole produces phosphenes progressively more distant from the fixation point. Successive stimulation of points along the orthogonal dorsoventral dimension produces a progressive change in phosphene bearing. These results confirm the general view of cortical organization derived from field defect studies in man, and from anatomical and electrophysiological studies in monkeys, and provide a new tool for more detailed study of retinotopic projections in man.

Adult↗
PubMed1978

Extreme myopia produced by modest change in early visual experience.

Chicks whose vision was restricted to the frontal visual field became extremely myopic (mean, -10 diopters; maximum, -24 diopters) and had eyes of increased axial length. Animals restricted to lateral field vision did not differ from normal animals. Monocular deprivation of form vision also produced myopia and eye enlargement and, in addition, produced increased anterior chamber depth.

Animals↗