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Biomedical subjects

J Rabin

Publications and source records attributed to J Rabin.

At least 37 records · Page 2Linked to original sources
PubMed1994

Visual evoked potentials through night vision goggles.

Night vision goggles (NVG's) have widespread use in military and civilian environments. NVG's amplify ambient illumination making performance possible when there is insufficient illumination for normal vision. While visual performance through NVG's is commonly assessed by measuring threshold functions such as visual acuity, few attempts have been made to assess vision through NVG's at suprathreshold levels of stimulation. Such information would be useful to better understand vision through NVG's across a range of stimulus conditions. In this study visual evoked potentials (VEP's) were used to evaluate vision through NVG's across a range of stimulus contrasts. The amplitude and latency of the VEP varied linearly with log contrast. A comparison of VEP's recorded with and without NVG's was used to estimate contrast attenuation through the device. VEP's offer an objective, electrophysiological tool to assess visual performance through NVG's at both threshold and suprathreshold levels of visual stimulation.

Contrast Sensitivity↗
PubMed1994

Optical defocus: differential effects on size and contrast letter recognition thresholds.

PURPOSE: To determine if optical defocus produces a greater reduction in visual acuity or small-letter contrast sensitivity. METHODS: Letter charts were used to measure visual acuity and small-letter contrast sensitivity (20/25 Snellen equivalent) as a function of optical defocus. Letter size (acuity) and contrast (contrast sensitivity) were varied in equal logarithmic steps to make the task the same for the two types of measurement. RESULTS: Both visual acuity and contrast sensitivity declined with optical defocus, but the effect was far greater in the contrast domain. However, measurement variability also was greater for contrast sensitivity. After correction for this variability, measurement in the contrast domain still proved to be a more sensitive (1.75x) index of optical defocus. CONCLUSIONS: Small-letter contrast sensitivity is a powerful technique for detecting subtle amounts of optical defocus. This adjunctive approach may be useful when there are small changes in resolution that are not detected by standard measures of visual acuity. Potential applications include evaluating the course of vision in refractive surgery, classification of cataracts, detection of corneal or macular edema, and detection of visual loss in the aging eye. Evaluation of candidates for occupations requiring unique visual abilities also may be enhanced by measuring resolution in the contrast domain.

Adult↗
PubMed1994

Flicker detection through night vision goggles.

Visual performance through night vision goggles (NVG's) is commonly assessed with letter charts or other static displays. Few attempts have been made to evaluate dynamic aspects of vision through NVG's. Such information may be used to better predict human performance and guide the development of improved devices. In this study, contrast thresholds for detection of flickering targets were measured through NVG's across a range of ambient conditions. A comparison of measurements with and without NVG's indicated that flicker detection is limited by the contrast and luminance of the NVG display. The contrast limitation is largely independent of stimulus flicker frequency. Increasing the transfer of static contrast and/or luminance through NVG's will also improve dynamic visual performance.

Aerospace Medicine↗
PubMed1993

Size induction transcends the cardinal directions of color space.

Certain psychophysical phenomena occur separately for color and for luminance stimulation. Separate psychophysical effects have also been elicited along different directions in equiluminant colour space. Whereas in most studies in which separate luminance and color effects have been reported the authors have used successive-adaptation approaches, less is known about the separateness of color and luminance processing under simultaneous conditions. A study is reported in which simultaneous size induction was examined for several different color directions thought to be 'cardinal' for early stages of processing. The perceived size of a test object was influenced by the size of the surrounding objects regardless of the color direction of the test and induction objects. The results indicate that simultaneous size induction occurs at a level of processing at which information conveyed by color and by luminance mechanisms is compared and contrasted to influence visual perception.

Attention↗
PubMed1993

Vernier acuity through night vision goggles.

Night vision goggles (NVG's) are being used increasingly in military and civilian environments. Despite the use of these devices, relatively few tests exist to assess visual performance through NVG's. Hyperacuity tasks may provide a sensitive index of performance through night vision devices. In this study, grating vernier acuity was measured through NVG's. As reported previously, a power law relation was observed between vernier acuity and stimulus contrast. Comparison of vernier acuity with and without NVG's indicated that performance is limited by the contrast transfer of the device. Vernier acuity measurements can be used to assess the quality of vision and quantity of contrast transferred through night vision devices.

Adult↗
PubMed1993

Estrogen receptor variant and hypertension in women.

Eighty-eight women visiting a gynecologist were tested for an estrogen receptor B-variant allele. The women were ethnically and racially homogeneous to a large degree. They were from a suburb of Long Island, and most were white. The 12% incidence of hypertension in women with the estrogen receptor wild-type allele is comparable to the 13-32% incidence in the general population of women aged 55-64 years. However, the 48% incidence of hypertension in women with the estrogen receptor B-variant allele is considerably higher than in the general population of women in this age group. We conclude that the presence of the estrogen receptor B-variant allele might have increased the prevalence of hypertension in the women in this study.

Age Factors↗
PubMed1993

Application of the spatiochromatic visual evoked potential to detection of congenital and acquired color-vision deficiencies.

Visual evoked potentials were recorded in response to spatiochromatic stimuli modulated in different directions in cone-activation color space from subjects with congenital and acquired color defects. This technique was effective for detection and classification of both mild and severe forms of congenital deficits. Results suggest that the visual evoked potential is useful for early identification of color abnormalities in acquired deficits such as diabetes and that it is sensitive enough to detect regional retinal losses of sensitivity (e.g., as in central serous choroidopathy). The spatiochromatic visual evoked potential provides a systematic and sensitive indication of different color-vision anomalies.

Adult↗
PubMed1993

Spatial contrast sensitivity through aviator's night vision imaging system.

Visual acuity is often used to assess vision through image intensifying devices such as night vision goggles (NVG's). Fewer attempts have been made to measure contrast sensitivity through NVG's. Such information would be useful to better understand contrast processing through NVG's under various stimulus conditions. In this study, computer-generated letter charts were used to measure contrast sensitivity through third generation NVG's for a range of letter sizes. The red phosphor of a standard color monitor proved to be an effective stimulus for third generation devices. Different night sky conditions were simulated over a 3 log unit range. The results illustrate the profile of contrast sensitivity through third generation NVG's over a range of night sky conditions. Comparison of measurements through NVG's to measurements obtained without the device but at the same luminance and color distinguish between effects of luminance and noise on contrast sensitivity.

Adult↗
PubMed1992

Perceptual ambiguity and the short wavelength sensitive visual pathway.

Visual illusions and ambiguous figures are difficult to perceive when presented in a manner which stimulates only chromatic pathways. This perceptual limitation could indicate that these pathways are unable to mediate form perception, or it may reflect the relative visibility of the stimulus, regardless of the pathway utilized. To examine this issue, an ambiguous figure (illusory Necker cube) was presented to the short wavelength sensitive (S) cone pathway which is thought to convey only chromatic signals. Although few observers could recognize the cube when presented in isolation to S cones, the same reduction in recognition was found when the cube was detected by achromatic pathways at a level of visibility comparable to that conveyed by S cones. Our results indicate that for this object recognition task, visibility of the stimulus is the relevant variable, rather than the particular pathway traversed. Prior experience was also found to be important determinant of object recognition.

Color Perception↗
PubMed1992

Lightness induction in the S-cone pathway.

Lightness induction is classically regarded as a contrast phenomenon limited to pathways which process luminance information. To determine if lightness induction can also occur in the chromatic domain, this phenomenon was studied with stimuli visible only to the short wavelength sensitive (S)-cones which have post-receptoral connections limited to chromatic pathways. The lightness of an object visible only to S-cones was found to be dependent on the relative intensity of its background in a manner similar to achromatic, luminance stimuli. Less intense (dark) backgrounds made the object appear lighter, while more intense (light) backgrounds made the same object appear darker. These results indicate a commonality among lightness induction effect in the processing of chromatic and luminance information.

Adaptation, Ocular↗
PubMed1992

Cortical potentials evoked by short wavelength patterned light.

Pattern-evoked cortical potentials (PECPs) were recorded in response to the onset of blue and black, square wave gratings superimposed on a bright orange background. Several lines of evidence, including spectral sensitivity and the absence of response in a tritanopic subject, indicate that the measured cortical potentials reflect input from S cones. Spatial and temporal tuning of this response are comparable to psychophysical measures of the S-pathway. In agreement with previous studies of achromatic and chromatic spatial processing, a comparison of the response to patterns of different complexity indicates that spatial processing in the S-pathway can be described by linear systems analysis. An oblique effect for the S-pathway is demonstrated. Additional findings which bear on the nature of postreceptoral processing in the S-pathway are considered. Included are measurements from a patient with diabetic retinopathy. This study underscores the potential importance of the S-pathway for spatial information processing.

Adult↗
PubMed1991

Incidence of an estrogen receptor polymorphism in breast cancer patients.

We previously identified a polymorphism in the human estrogen receptor (ER) gene, within the coding region for the protein's amino terminal B-domain. In estrogen receptor-positive (ER+) breast tumors, the variant allele was preferentially associated with lower levels of ER, and was clinically correlated with frequent spontaneous abortions. DNA sequencing revealed a point mutation that changes codon 86 from Ala to Val and a silent mutation in codon 87. Because we initially detected the variant allele by analyzing RNA, only those tissues in which the ER gene is actively expressed were suitable for genotype analysis. We now describe an assay that uses genomic DNA as the substrate for determining the ER B genotype, DNA containing the polymorphic region of the ER gene is amplified by the polymerase chain reaction, then the amplified DNA is hybridized with radiolabeled oligonucleotide probes complementary to the wild type and variant ER alleles. This method allowed us to determine the ER B genotype of women with ER+ and ER- tumors, starting with minute amounts of DNA from frozen or paraffin embedded tissues. ER B genotyping was also performed on women without breast cancer using DNA extracted from blood cells. The combined results from analyses of RNA and DNA from 300 breast cancer patients showed that 12% were heterozygotes. In the ER+ group (n = 183), 11.5% carried the variant gene compared to 12.8% in the ER-negative group (n = 117) (chi 2 = 0.11; df = 1; p greater than 0.25).(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
PubMed1991

The concentration of lactic acid in breast milk following maximal exercise.

The purpose of this study was to investigate the concentration of lactic acid in breast milk following maximal exercise. Seven active postpartum women (2 to 24 months) were exercised to maximum on a treadmill (VO2 max = 37.0 +/- 13.7 ml.min-1.kg-1). Blood was sampled via finger prick at rest before exercise and 5 minutes postexercise; milk was collected via self expression at rest before exercise and at 10 and 30 minutes postexercise. Both blood and milk were analyzed for lactic acid via enzymatic methods. Following maximal exercise, a significant increase in the concentration of lactic acid was found in the blood at 5 minutes postexercise and breast milk at 10 minutes postexercise. Although elevated, the lactic acid concentration of the 30-minute sample of breast milk was not significantly different from the resting sample. Maximal exercise can result in significant increase in lactic acid concentration in breast milk. Further research is needed to demonstrate whether the taste of the milk is affected.

Breast Feeding↗
PubMed1990

Visual acuity and contrast sensitivity of the S cone pathway: preliminary measures with letter charts.

Letter charts were used to measure visual acuity and peak contrast sensitivity of the short wavelength sensitive (S cone)-pathway. The accommodative response was monitored retinoscopically. The mean visual acuity (0.92 logMAR) and spatial contrast threshold (8.7%) were comparable to values reported elsewhere, and variability was relatively low. Both S-pathway acuity and contrast sensitivity were selectively reduced in one patient with central serous retinopathy and in another with retinitis pigmentosa. These simple spatial tests offer an additional index of S-pathway integrity which will be useful for detection and evaluation of ocular disease.

Accommodation, Ocular↗
PubMed1989

Teenagers' awareness of the acquired immunodeficiency syndrome and the impact on their sexual behavior.

One hundred female teenagers attending a teenage pregnancy program were studied to determine the extent of their awareness about acquired immunodeficiency syndrome (AIDS) and the impact of such knowledge on their sexual behavior. Ninety-eight knew that AIDS is a disease, 45 stated that it is fatal, and all knew that it can be transmitted by sexual intercourse. After becoming aware of AIDS, 59 changed their sexual habits, 41 decreased their number of sexual partners, and 13 who had not used condoms started using them. However, only seven obtained more information about their partners' sexual and social histories, and half of those who decreased their number of partners still continued relationships with more than one. The survey showed that the publicity about AIDS has resulted in a favorable change in the sexual practices of these teenagers. However, it also indicated a need for further improvement in specific areas of education, such as the value of obtaining more information about sexual partners, more awareness of the importance of multiple-partner relationships in the spread of AIDS, and more emphasis on the important role of condoms in preventing AIDS virus transmission.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Antitranspirant associated abscisic Acid effects on the water relations and yield of transplanted bell peppers.

Greenhouse and field experiments were performed to determine if increased leaf resistance induced by exogenous application of abscisic acid (ABA) could enhance the water status of transplanted bell pepper seedlings. Seedling survival and yield were also monitored in the field experiment. When seedlings were transplanted into either wet or dry potting mix in the greenhouse, ABA increased leaf resistance and leaf water potential. In the field, plots were irrigated either immediately after, or 1 day after transplanting. Under both treatments, ABA application resulted in increased leaf resistance and water potential, but seedling survival and yield were enhanced due to ABA only in plots which were irrigated 1 day after transplanting. It is concluded that antitranspirant application can reduce transplant shock and increase yield of bell pepper.

Journal Article↗
PubMed1985

An unusual case of antimetropia.

Antimetropia is a condition in which one eye is myopic and the fellow eye is hyperopic. This report describes functional and optical characteristics of a patient with a substantial degree of antimetropia.

Amblyopia↗