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Biomedical subjects

S A Klein

Publications and source records attributed to S A Klein.

At least 127 records · Page 7Linked to original sources
PubMed1985

Hyperacuity thresholds of 1 sec: theoretical predictions and empirical validation.

Bisection thresholds were measured as a function of the separation of the lines. For separations of less than 1.5 min, the addition of flanking lines facilitates bisection so that thresholds of less than 1 sec for discriminating the direction of offset could be reliably obtained. For larger separations an interval could be bisected to an accuracy of 1 part in 60. Experiments varying the length, luminance, and overlap of the lines suggest that different cues are used in these two regimes. A dual space-size analysis is presented that can account for these bisection thresholds over a wide range of experimental conditions. This quantitative analysis produces viewprints of the stimuli (analogous to the voiceprint of audition). Each viewprint shows the output of many spatial filters of different positions and sizes. A new filter shape is introduced that has advantages for modeling the visual system. The sensitivity of each filter is fixed by the contrast-response function. The analysis further shows that the limiting factors in spatial hyperacuity are both the contrast-response function and the spatial grain.

Discrimination, Psychological↗
PubMed1985

Double-judgment psychophysics: problems and solutions.

Many paradigms for comparing identification thresholds with detection thresholds require the observer to make double judgments. We show that these paradigms can produce misleading results because of response biases and attentional shifts. For example, the subject's response bias plus correlated noise can mimic inhibition between channels. Some of these same problems can affect single-judgment paradigms. A detailed analysis of the double-judgment forced-choice paradigm reveals that there are a multiplicity of optimal strategies, some of which enhance identification over detection. Several improved analysis techniques for minimizing the effects of cognitive factors are proposed for both the double-judgment forced-choice paradigm and the double-judgment rating-scale paradigm. A classification scheme for distinguishing different types of interactions and correlations is developed. When the new rating-scale algorithm is applied to the detection of well-separated spatial frequencies, substantial masking but negligible inhibition is found. The rating-scale paradigm is shown to be useful in revealing not only the sensitivity and the interactions of the underlying mechanisms but also the observer's information-processing strategies.

Attention↗
PubMed1984

Detection and discrimination of the direction of motion in central and peripheral vision of normal and amblyopic observers.

This paper describes the "motion" properties of the amblyopic fovea and compares them to the normal periphery. Specifically, thresholds for detection of the displacement of a grating pattern, and for discrimination of displacement direction were measured. The main findings of these experiments were: in the central vision of both normal and amblyopic observers, unreferenced displacement are detected with an accuracy equal to the observer's grating acuity; in the normal periphery, unreferenced motion thresholds fall off at a slower rate than does grating acuity; in amblyopic eyes, displacement thresholds are most elevated centrally; the addition of an abutting reference improves detection of motion for the normal fovea and in anisometropic amblyopes, but elevates motion thresholds in both the normal periphery and in the fovea of amblyopes with strabismus. The adequacy of the normal periphery as a model for the central vision of amblyopes is discussed.

Adult↗
PubMed1984

Opponent-movement mechanisms in human vision.

A vertical grating that sinusoidally reverses contrast can be synthesized from two identical component gratings that move with equal velocities in opposite directions (leftward and rightward). Such a counterphase grating is used as a suprathreshold masking pattern. When the mask is of low spatial frequency and is modulated rapidly, a test pattern consisting of an increment of the rightward component and an equivalent simultaneous decrement of the leftward component is highly detectable compared with simultaneous increments or decrements of both components. The visibility of the opponent-movement test signal is strongly facilitated by high-contrast masks. This facilitation is accompanied by a high sensitivity for judging the direction of motion of the test. These results show that certain detection mechanisms are highly sensitive to the difference of the rightward and leftward components. However, when the mask is of threshold contrast, the rightward- and leftward-moving test components appear to be detected independently. A high-contrast grating that rapidly moves in one direction strongly masks gratings moving in the same or opposite direction; this shows that moving patterns are not detected by unidirectional mechanisms when contrast is clearly suprathreshold. The results may be explained by a model with mechanisms that are excited by one direction of motion and inhibited by the opposite direction.

Discrimination Learning↗
PubMed1984

The development of vernier acuity in infants.

Vernier and grating acuity were measured in infants up to 6 months of age using a two-alternative forced-choice preferential looking technique. Vernier resolution was measured using a horizontal vernier grating. The grating was presented on half of the screen while the other half contained horizontal lines which were continuous with the vernier grating. Movement artifacts were eliminated by making both halves of the display move as the offsets were introduced in half of the display field. Vernier acuity, like grating acuity, improved about 3 octaves over the first 6 months of life. Moreover, the vernier resolution of infants, as of adults, was better than grating resolution.

Child Development↗
PubMed1983

Spatial localization in normal and amblyopic vision.

Spatial localization was investigated for each eye of amblyopic observers using a bisection paradigm. The stimuli were comprised of a grating composed of bright lines, and a test line. The test line was either placed above the grating (bisection-no overlap) or within the row of lines comprising the grating (bisection-with overlap) and thresholds for each bisection task were measured as a function of the fundamental spatial frequency of the grating. Vernier thresholds were also measured. For the nonamblyopic eyes at low spatial frequencies, bisection thresholds were a constant fraction ("Weber" fraction) of the space to be bisected, while at high spatial frequencies thresholds were approximately a constant retinal distance (a hyperacuity). However the spatial localization of an amblyopic eye depends upon both the type of amblyopia, and the stimulus configuration. Specifically, for anisometropic amblyopia, spatial localization (bisection-no overlap) and vernier, when scaled to the resolution losses, were normal. However, spatial adjacency (bisection with overlap), while enhancing the spatial localization of nonamblyopic eyes at high spatial frequencies, markedly elevated thresholds in the amblyopic eyes of anisometropic amblyopes. Strabismic amblyopes on the other hand show disturbances in both spatial localization tasks which can not be accounted for on the basis of reduced resolution. Their results are characterized by an absence of a constant Weber fraction at low spatial frequencies and "crowding" effects at high spatial frequencies. For strabismic amblyopes, the optimal localization thresholds were similar to the Snellen threshold, while for anisometropic amblyopes, the optimal localization thresholds were several times better than the Snellen threshold.

Adult↗
PubMed1983

Pregnancy after spinal cord injury: altered maternal and fetal response to labor.

Four pregnancies in three patients with spinal cord injury are presented. The major complications encountered include anemia, pyelonephritis, decubiti, premature labor, precipitate labor, and autonomic hyperreflexia. Autonomic hyperreflexia, a severe mass autonomic reflex response to labor, is associated with tachycardia, hypertension, headache, diaphoresis, and severe anxiety. It is probably due to increased norepinephrine release, as very high urinary metanephrines were measured in the latter two cases presented. Maternal and fetal physiology in labor are altered. Despite severe maternal and fetal stress responses, no fetal depression was observed.

Adult↗
PubMed1981

Continuous fetal monitoring following third-trimester amniocentesis.

One hundred forty-six patients were monitored for up to 2 hours after third-trimester amniocentesis. The patterns of uterine and fetal activity, as well as fetal heart rate, were analyzed using the criteria for nonstress and contraction stress testing. There was a clear relationship between these observations and perinatal outcome. Postamniocentesis monitoring was associated with an Apgar score of 6 or less in only 10% of cases with reactive patterns, compared with in 75% of cases with nonreactive patterns and reduced variability and in all cases with late-component deceleration. All cases of immediate fetal jeopardy were detected and there was no fetal loss. Postamniocentesis monitoring appears to offer significant prognostic information for perinatal outcome in high-risk pregnancy.

Amniocentesis↗
PubMed1980

Intravenous dexamethasone for prevention of neonatal respiratory distress: A prospective controlled study.

A trial of intravenous dexamethasone for prevention of neonatal respiratory distress syndrome was carried out prospectively. There were 112 treated and 188 control patients, matched for gestational age, birth weight, rupture of membranes, and antepartum diagnosis. No short-term deleterious effects on mother or infant were demonstrable. There was an increased incidence of cesarean section and puerperal infection in the treated patients. This was not related to the steroid therapy. There was no increased incidence of infection in the treated neonates. At 28 to 33 weeks' gestation, the treated newborn infants had one half the perinatal mortality and one fourth the incidence of severe respiratory distress syndrome seen in the controlls. Under 28 weeks, and from 34 to 36 weeks, no difference between treated and control groups was observed. Intravenous dexamethasone is effective in reducing perinatal mortality from respiratory distress syndrome in premature infants delivered between 28 to 33 weeks' gestation.

Bacterial Infections↗
PubMed1980

The role of colposcopy in the management of cervical intraepithelial neoplasia during pregnancy and postpartum.

We made a colposcopic study of 149 pregnant patients with suspicious or positive Papanicolaou smears. Characteristic changes in the colposcopic images were noted to be physiologic eversion of the squamocolumnar junction, glandular hypertrophy and decidual reaction. Fourteen percent of the patients with suspicious Papanicolaou smears were normal by colposcopic examination. Sixteen percent of colposcopic interpretations of the pregnant cervix suggested CIN when in fact none was present on tissue specimens obtained by directed biopsies. There was a good correlation between colposcopic clinical diagnosis and directed tissue biopsies (79%). Furthermore, there was a strong correlation between colposcopically directed tissue biopsies and subsequent cone and hysterectomy specimens (29 cases). All cases with suspicious cytology and CIN based on colposcopic findings (130 patients with satisfactory colposcopic examinations) were managed conservatively. No invasive neoplasia was subsequently detected in this group. Morbidity for colposcopically directed biopsies in pregnancy was negligible. No massive hemorrhage, premature labor, abortion or infection occurred. Treatment for CIN was accomplished following the puerperium by cryocauterization (101 cases), conization (8 cases) or hysterectomy (21 cases). Colposcopy cannot be a substitute for histologic diagnosis. However, it supplies enough data to avoid unnecessary cone biopsies. Only 19 diagnostic cone biopsies were performed during pregnancy with the indication of positive cytology and unsatisfactory colposcopy.

Adolescent↗
PubMed1979

Fetal blood and tissue pH with moderate bradycardia.

Eleven patients with moderate fetal bradycardia in labor were studied by fetal scalp blood pH, continuous tissue pH, and umbilical arterty pH at delivery. The neonatal outcomes and biochemical data demonstrated that moderate fetal brdycardia does not indicate fetal distress.

Female↗
PubMed1979

The relationship of heart rate patterns and tissue pH in the human fetus.

The relationship between different FHR patterns and fetal tissue pH in 68 high-risk gravidas in labor was analyzed. A tissue pH electrode was placed in the fetal scalp and tissue pH recorded on a fetal monitor every 15 seconds along with uterine contractions and continuous fetal heart rate. The tissue pH changes correlated with the FHR patterns in a manner consistent with current concepts of fetal stress. Trend monitoring of fetal tissue pH in labor may prove useful in the management of high-risk patients in labor.

Apgar Score↗
PubMed1979

Diagnosis of congenital mitral and aortic stenosis from the fetal electrocardiogram.

A case of congenital mitral and aortic stenosis diagnosed from the fetal electrocardiogram (FECG) during labor is presented. Cardiologic work-up and autopsy findings in the neonate confirmed the diagnosis. This is the first case in which prenatal diagnosis of a specific anatomical lesion of the heart was made from the FECG and confirmed clinically as well as at autopsy.

Adult↗
PubMed1979

Intrapartum fetal cardiac arrhythmias.

Fifteen cases of fetal cardiac arrhythmia were detected by direct fetal electrocardiogram (FECG) during intrapartum fetal monitoring. The frequency of arrhythmia of 12.4/1000 monitored births. Thirteen of the arrhythmias were supraventricular. Atrial bigeminy was the most commonly observed arrhythmia, followed by atrial trigeminy. Two cases of ventricular arrhythmia were noted, one of which was a case of ventricular tachycardia. Arrhythmias were not related to drug treatment or to stage of labor. Variable decelerations occurred in association with arrhythmias in 73% of the cases. There were no nuchal cords seen at delivery, nor were there any instances of intrapartum fetal distress, fetal acidosis, or low Apgar scores associated with any arrhythmia. All arrhythmias resolved spontaneously without treatment. The neonatal course was uncomplicated in all cases. Intrapartum fetal arrhythmia is best detected by direct FECG. Appropriate management should include close observation for ominous fetal heart rate (FHR) patterns and fetal acid-base-studies. At present, there is no indication for drug treatment of intrapartum arrhythmia.

Arrhythmias, Cardiac↗