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Biomedical subjects

I Abramov

Publications and source records attributed to I Abramov.

At least 37 records · Page 2Linked to original sources
PubMed1985

Saccades and small-field optokinetic nystagmus in infants.

Developmental studies of infant eye movements may be a useful tool in the early diagnosis of visual abnormalities. We have measured saccades made by infants during the free scanning of stimuli differing in attentional value. When viewing stimuli with high attentional value, infants made saccades that had adult-like peak velocity/amplitude (main sequence) relationships, while for less interesting stimuli, their saccades were slower; saccadic oscillations were also more frequent for these stimuli. In studies of small-field horizontal and vertical optokinetic nystagmus, with binocular viewing, infants' horizontal OKN was of higher frequency and lower amplitude than their vertical OKN. Within vertical OKN, there was a clear asymmetry with reduced responsiveness to downward moving stimuli. This asymmetry declined for older infants; possible interpretations for this change are discussed.

Adult↗
PubMed1985

Changes in visual functions of children exposed as infants to prolonged illumination.

The visual system can be modified by early experience. Many infants requiring extensive medical treatment spend time in neonatal intensive care units in which they experience prolonged and relatively intense illumination. Visual functions were measured in a group of 7-year-old children who, as infants, were in intensive care for treatment of neonatal jaundice. Using procedures disguised as games, these children were tested for spatial and temporal resolution, receptor functions, and binocular vision. Especially in children whose eyes had not been shielded, deficits were found in color vision, spatial contrast sensitivity, and stereopsis, but not in rod vision.

Child↗
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↗
PubMed1982

The retina of the newborn human infant.

We have examined a pair of eyes from a normal, full-term infant who died at 8 days as a result of accidental injury. Eyes were obtained immediately after death, fixed, and sectioned for light microscopy. Results from both eyes were substantially the same. The macular region was still drastically immature at 1 week. Even though a foveal depression existed, all cell layers were still present across it. Furthermore, the inner nuclear layer was divided into two separate layers. The receptor layer was reduced to one or two cells thick; receptors had both inner and outer segments, but they were very short and stumpy. The region of immaturity covered about 5 degrees of the retina. These findings suggest that the central region of a human infant's retina is probably not fully functional at birth.

Humans↗
PubMed1977

Color vision in the peripheral retina. I. Spectral sensitivity.

Spectral sensitivity was measured by heterochromatic flicker photometry both in the fovea and at 45 degrees in the periphery, using a 1200 troland standard. At each location, sensitivity functions were obtained using both large and small targets. While the foveal functions were normal, the peripheral ones showed a large enhancement in sensitivity to short wavelengths relative to long wavelengths. Similar results in the past had been criticized on the ground that they might have been due to differential chromatic adaptation of cone mechanisms. In this study such an interpretation was ruled out by additional control experiments including varying luminance and wavelength of the standard light. The possibility of a rod contribution to the peripheral functions could not be eliminated although several different techniques, including the Stiles-Crawford effect, were used to try to isolate cone mechanisms.

Adult↗
PubMed1977

Color vision in the peripheral retina. II. Hue and saturation.

Hue and saturation of spectral lights were measured (direct scaling) in the fovea and at 45 degrees in the periphery; all lights were of equal photopic retinal illuminance (1200 trolands). At each retinal location both large and small targets were used. As shown by previous studies, small peripheral targets appear desaturated and of uncertain hue, except long wavelengths which appear red. However, if target size is increased, saturation increases and a full range of hues is seen; the hue functions for large peripheral targets are comparable to foveal ones for very small targets. From a modified form of color matching, it was concluded that the color deficiency in the periphery is more tritanlike than deutanlike; this is strengthened by the observation, that, for small peripheral targets, hues are generally apportioned between two hue categories and the change from one to the other is at about 580 nm.

Adult↗
PubMed1966

Color vision.

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Animals↗