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Biomedical subjects

S Sokol

Publications and source records attributed to S Sokol.

At least 37 records · Page 2Linked to original sources
PubMed1989

Evoked potential and preferential looking correlates of the oblique effect in 3-month-old infants.

Sensitivity for vertical and horizontal gratings is higher than for obliquely oriented gratings, a phenomenon known as the oblique effect. We compared visual evoken potential and preferential looking estimates of the oblique effect in nonastigmatic 3-month-old infants and found that orientation effects occurred more frequently by visual evoked potential measure than by preferential looking.

Evoked Potentials, Visual↗
PubMed1989

The process of localizing a maternal messenger RNA in Xenopus oocytes.

The maternal mRNA Vg1 is localized to the vegetal pole during oogenesis in Xenopus. We have cultured oocytes in vitro to begin to understand how this localization occurs. Endogenous Vg1 mRNA undergoes localization when oocytes are cultured in vitro, and synthetic Vg1 mRNA injected into such oocytes is localized in the same fashion. Vg1 mRNA is associated with a detergent-insoluble fraction from homogenized oocytes, suggesting a possible cytoskeletal association. The use of cytoskeletal inhibitors reveals a two-step process for localizing Vg1 mRNA. Microtubule inhibitors such as nocodazole and colchicine inhibit the localization of Vg1 mRNA in late stage III/early stage IV oocytes, but have no effect on Vg1 mRNA once it is localized. The microfilament inhibitor cytochalasin B, however, has little effect on the translocation of Vg1 mRNA in middle-stage oocytes but causes a release of the message in late-stage oocytes. We propose a model for the localization of Vg1 mRNA in which translocation of the message to the vegetal cortex is achieved via cytoplasmic microtubules and the anchoring of the message at the cortex involves cortical microfilaments.

Actin Cytoskeleton↗
PubMed1988

Infant grating acuity is temporally tuned.

Studies of infant visual development have shown that acuity estimated with pattern visually evoked potential (VEP) techniques is higher than acuity estimated with preferential looking (PL) techniques. A major difference is that VEP stimuli are temporally modulated while PL stimuli are typically stationary. We measured PL acuity in 2-10-month-old infants for stationary gratings and for gratings phase alternating at 2.5, 7.5, 14 and 23 reversals/sec using a computer generated staircase method. The acuity functions were temporally tuned at 7.5 or 14 rev/sec for infants 3 months and older. Acuity for 7.5 and 14 rev/sec gratings was 0.5 to 1.0 octave higher than for stationary, 2.5 and 23 rev/sec gratings. When adults' grating acuity was measured foveally and 5 deg eccentrically, tuning occurred only for the eccentric targets, suggesting that the retinal area used by the infants to detect gratings acts like the adult perifovea. In a second experiment, VEP and PL acuity were both measured from the same infants using 14 reversals/sec gratings. The VEP/PL acuity difference was less for phase alternating gratings than for stationary gratings. The magnitude of the difference was age dependent, decreasing from 2 octaves at 2 months to 0.5 octave at 12 months. Even though the use of phase alternating gratings results in improved PL acuity, temporal modulation does not completely account for the difference between VEP and PL acuity.

Adult↗
PubMed1987

Electrophysiological evidence for the oblique effect in human infants.

Visually-evoked potentials (VEPs) were recorded from infants between the ages of 2 and 11 months in response to 2.5 c/deg main axis and oblique square wave gratings. The oblique effect first appears at 3 months of age; some infants showed smaller VEP amplitude and/or longer VEP latency for obliquely oriented gratings. Regarding the age of onset of the oblique effect, VEP data from this study agree with the results obtained with preferential looking (PL) studies which have directly paired vertical and oblique gratings, but the current study found that fewer infants show an oblique effect by VEP than by PL.

Aging↗
PubMed1985

Diagnosing functional visual deficits with the P300 component of the visual evoked potential.

The visual evoked potential (VEP) is routinely used to assess visual function, though it occasionally does not reflect a patient's conscious experience. Reports of normal flash or pattern VEPs obtained from blind persons are extreme examples of this problem. The difficulty in interpreting VEPs in light of such findings can be partly overcome by obtaining a cognitive component of the evoked potential, P300. We obtained traditional visual acuity measurements, pattern-reversal VEPs, and VEPs containing P300s from three patients with clinically diagnosed functional visual deficits. The P300s were obtained in response to stimuli that the patients claimed they could not see, supporting the clinical conclusions that malingering or hysteria was involved. The P300 component can be helpful in assessing the subjective visual experience of patients suspected of having functional visual loss.

Clinical Trials as Topic↗
PubMed1985

Contrast sensitivity in diabetics with and without background retinopathy.

Contrast sensitivity measurements were obtained from 64 patients with insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes mellitus who had normal Snellen acuity and minimal or no visible diabetic retinopathy. Contrast thresholds were determined for stationary gratings at six spatial frequencies, ranging from 0.5 to 22.8 cycles/degree (c/deg), and for 1.0-c/deg gratings phase-alternated at 15 Hz. Data from each group of diabetic patients were compared with data from age-matched normal subjects. We found that (1) patients with IDDM and no retinopathy had normal contrast sensitivity, (2) patients with NIDDM and no retinopathy had abnormal contrast sensitivity at only one spatial frequency (22.8 c/deg), and (3) patients with NIDDM and background retinopathy had abnormal contrast sensitivity at all spatial frequencies tested. We also found a dissociation of Snellen acuity and contrast sensitivity, indicating that contrast sensitivity can be used as an early index of changes in the retina not demonstrated by measurements of visual acuity.

Adolescent↗
PubMed1985

Reversible optic neuropathy due to carotid-cavernous fistula.

Optic nerve dysfunction occurred several weeks after traumatic carotid-cavernous fistula developed in a 21-year-old man. Vision was completely restored after the fistula was closed with an intra-arterial detachable balloon. By carefully monitoring visual function in patients with traumatic carotid-cavernous fistulas, delayed optic neuropathy can be recognized and treated successfully.

Adult↗
PubMed1985

Effect of stimulus orientation on the latency and amplitude of the VEP.

VEPs were recorded using 5.0 c/deg square wave gratings presented at vertical and oblique (45 deg) orientations and phase-alternated at two rates, 6 alternations/sec and 12 alternations/sec. In agreement with previous reports, VEP amplitude was smaller for obliquely oriented gratings than for vertically oriented gratings at both alternation rates. Unlike previous studies, however, the authors found that VEP latency was longer for obliquely oriented gratings at the slower (6/sec) alternation rate.

Adult↗
PubMed1985

Comparison of pattern VEPs and preferential-looking behavior in 3-month-old infants.

Studies of visual acuity in human infants between 1 and 6 months of age using the visual-evoked potential (VEP) and forced-choice preferential looking (FPL) have shown that acuity is one to two octaves higher by VEP estimates than by FPL estimates. In an attempt to study these differences, the authors obtained both VEP and FPL data from 26 3-month-old infants. VEP data were obtained with gratings of 0.31, 0.62, 1.25 and 2.50 cycles/deg, which were counterphase alternated at 2 Hz. FPL data were obtained for stationary gratings using either the method of constant stimuli or a staircase procedure. Our study revealed three major findings: (1) recordable VEPs can be obtained for spatial patterns that are below threshold by behavioral measures; (2) the use of different scoring criteria that yields comparable VEP and FPL group mean acuities does not yield a significant correlation between VEP amplitude acuity and FPL acuity for individual infants, probably because of the inherent "noise" in each technique; and (3) when VEP latency rather than amplitude is used to estimate acuity, there is a significant correlation between electrophysiology and behavior.

Discrimination, Psychological↗
PubMed1984

Prosodic features and the intelligibility of accelerated speech: syntactic versus periodic segmentation.

An experiment is reported in which subjects heard paragraph-length samples of time-compressed speech which were interrupted for intermediate reports either on a simple periodic basis or at points corresponding to sentence and major clause boundaries. The passages were spoken in a normal prosodic pattern, in list intonation, or were electronically processed to produce otherwise normal speech specifically deprived of pitch variation. Decrease in intelligibility scores with increasing speech rate was accompanied by a significant effect of place of interruption for report and of the prosodic pattern in which the passages were heard. Interactions among these variables were interpreted to suggest ways in which prosody ordinarily facilitates the determination of syntactic structure in connected speech.

Humans↗
PubMed1983

Developmental changes in the human visual system as reflected by the latency of the pattern reversal VEP.

Pattern reversal visually evoked potentials (VEPs) were recorded from 439 infants and young children ranging in age from 1 month to 5 years in response to large and small checks. Qualitative analysis of the VEP wave form showed that the first major positive component, P1, is consistently present at all ages, while the frequency of occurrence of later positive components is more variable. The proportion of infants showing late positive components increases with age; by 1 year, the frequency of occurrence of late components for large checks is more adult-like than for small checks. The latency of P1 was analyzed quantitatively. Results showed that P1 latency decreases rapidly during the first year of life for both large and small checks and that the time course of the latency change differs as a function of check size. VEPs to large checks attain adult-like P1 latency values by about 1 year of age, while the P1 latency of VEPs to small checks has still not reached adult levels by 5 years of age. Data from 12 infants tested longitudinally between 1 and 7 months of age using both checkerboards and square wave gratings show no difference in P1 latency between checkerboards and gratings comprised of large (30-240 min) pattern elements, but for patterns with small (7.5 and 15 min) elements, P1 latency to checks is significantly longer than P1 latency to stripes. These results are explained on the basis of the difference in the fundamental spatial frequency between checks and stripes.

Attention↗
PubMed1983

Evoked potential estimates of visual accommodation in infants.

Pattern reversal visually evoked potentials (VEPs) were recorded from infants between 2 and 5 months of age in order to measure their accommodative performance over a 9 diopter range (10-150 cm). Accommodation was stimulated by placing minus spherical lenses of increasing power in front of the infant's eyes and by changing the infant's distance from the stimulus. VEP latency measurements indicated that the infant's ability to maintain a zone of clear vision changes with age and pattern element size. For large checks (60 min arc), most 2- to 4-month old infants were able to maintain clear vision over the range of 9 diopters. When small checks (15 min arc) were used, the majority of 4- to 5-month old infants were unable by VEP measures to accommodate beyond 5-6 diopters. This decline in the infant's zone of clear vision with decreasing check size is due primarily to the relatively large depth of focus and poor visual resolution of the infant eye. In a small group of infants, accommodation was assessed both electrophysiologically by VEP recording and behaviorally using a preferential looking technique. Results indicated better accommodation by VEP estimates than by behavioral measures.

Accommodation, Ocular↗
PubMed1983

Comparison of the spatial response properties of the human retina and cortex as measured by simultaneously recorded pattern ERGs and VEPs.

Electroretinograms and visual evoked potentials were simultaneously recorded from adult subjects using a checkerboard pattern stimulus reversing at 0.94, 3.75 and 7.5 Hz. Two contrast levels were used: 30 and 85%. The data obtained from the cortex (VEPs) show spatial tuning properties for all temporal frequencies at both contrast levels, with the peak of the amplitude-check size function occurring between 15 and 30 min. Tuning properties were found at the retina but only at the high contrast level and for the faster (3.75 and 7.5 Hz) temporal frequencies. The results demonstrate that spatial tuning is present in the human retina but not under as wide a range of conditions as found at the cortex.

Adult↗
PubMed1983

Evoked potential and preferential looking estimates of visual acuity in pediatric patients.

Pattern visual evoked potentials (VEPs) and behavioral visual acuity measured with forced-choice preferential looking techniques (FPL) were obtained from 172 pediatric patients between the ages of 4 months and 10 years. More children younger than 2 years of age successfully completed monocular testing by pattern VEP than by FPL methods. For children older than 2 years, we were equally successful in completing each of the two tests. Of those children who completed both tests, the VEP results agreed with Snellen, Allen, and "E" acuity measures more often (66%) than did the FPL results (50%). Both tests were more sensitive than Allen single characters in detecting interocular acuity differences in children younger than 3 years of age.

Age Factors↗
PubMed1983

Abnormal evoked potential latencies in amblyopia.

The latency of the first (P1) and second (P2) major positive waves of the pattern reversal visual evoked potential (VEP) for small checks (15 minutes of arc) was measured in 68 visually normal children and 32 amblyopic children with mild to moderate visual acuity losses. In the normal children there were no P1 and P2 interocular latency differences. The amblyopic children showed longer P1 latencies and shorter P2 latencies in their amblyopic eye than their normal fellow eye. These findings can be accounted for by a selective loss of the contrast-specific evoked potential mechanisms in amblyopia. The 'shorter' P2 latency obtained from amblyopic eyes for small checks is a reflection of the luminance responses that are normally elicited by larger (60 minute) checks.

Amblyopia↗
PubMed1983

Recording the contralateral PERG: effect of different electrodes.

A pattern electroretinogram (PERG) can be recorded when the eye wearing the electrode is occluded and the stimulus is viewed with the other eye. We find that this phenomenon occurs when an Arden gold foil electrode is used, but not when either an ERG-Jet lens or a scleral lens electrode is used. Therefore, a corneal-type electrode should be used in PERG recording situations where the fellow eye is not occluded.

Adult↗
PubMed1983

The visual evoked potential in glaucoma and ocular hypertension: effects of check size, field size, and stimulation rate.

In order to determine the optimum stimulus conditions for the detection of optic nerve damage due to glaucoma and ocular hypertension, checkerboard pattern reversal visual evoked potentials (VEPs) were recorded from 20 glaucoma patients, 20 ocular hypertensive patients, and 20 age-matched normals. Two check sizes (12' and 48'), two field sizes (14 degrees and 28 degrees), and two alternation rates (1.9 and 7.5 alt/sec) were used. All subjects had visual acuities of 20/40 or better in each eye and equal pupils of 2 to 5 mm diameter. The largest number of VEP abnormalities were found with large checks (48') reversing at a fast rate (7.5 alt/sec). After correcting for the effects of age, visual acuity, and pupil size, 16 of 30 eyes with glaucomatous visual field defects had abnormally long VEP latencies under this condition (beyond the 99% confidence limit of the normal subjects). Nine of 40 ocular hypertensive eyes also had abnormally long latencies. Increased pattern VEP latency was significantly correlated with both the severity and location of visual field defects and the degree of cupping and pallor of the optic disc. VEP latency was not significantly related to intraocular pressure.

Adult↗