Biomedical subjects

S E Barrett

Publications and source records attributed to S E Barrett.

14 recordsLinked to original sources

PubMed2001

Spectroscopic evidence for the localization of Skyrmions near nu = 1 as T --> 0.

Optically pumped nuclear magnetic resonance measurements of 71Ga spectra were carried out in an n-doped GaAs/Al(0.1)Ga0.9As multiple quantum well sample near the integer quantum Hall ground state nu = 1. As the temperature is lowered (down to T approximately 0.3 K), a "tilted plateau" emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional Skyrmions.

Journal Article↗

PubMed2000

Recognition and sex categorization of adults' and children's faces: examining performance in the absence of sex-stereotyped cues.

The ability of children and adults to classify the sex of children's and adults' faces using only the biologically based internal facial structure was investigated. Face images of 7- to 10-year-old children and of adults in their 20s were edited digitally to eliminate hairstyle and clothing cues to sex. Seven-year-olds, nine-year-olds, and adults classified a subset of these faces by sex and were asked, subsequently, to recognize the faces from among the entire set of faces. This recognition task was designed to assess the relationship between categorization and recognition accuracy. Participants categorized the adult faces by sex at levels of accuracy varying from just above chance (7-year-olds) to nearly perfect (adults). All participant groups performed less accurately for children's faces than for adults' faces. The 7-year-olds were unable to classify the children's faces by sex at levels above chance. Finally, the faces of children and adults were equally recognizable--a finding that has theoretical implications for understanding the relationship between categorizing and identifying faces.

Adult↗

PubMed1998

Health care needs of medically underserved women of color: The role of the Bureau of Primary Health Care.

The Bureau of Primary Health Care (BPHC) was developed to increase access to comprehensive primary and preventive health care and to improve the health status of medically underserved populations. Approximately 43 million Americans fall into this category, and the majority are poor, female, young, and uninsured. Under the Public Health Services Act, BPHC does not provide direct services, but rather assist local communities in identifying populations at risk of poor health outcomes and helps these communities through various programs. One of the newest initiatives of BPHC is the Office of Minority and Women's Health, developed with a mission to help reduce the disparities in the health status of women of racial and ethnic minority populations. This article outlines these disparities and discusses proposals for reducing them.

Ethnicity↗

PubMed1995

Electronic states in gallium arsenide quantum wells probed by optically pumped NMR.

An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < v < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T1 at v approximately 1 and v approximately 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.

Arsenicals↗

PubMed1993

Theory-based correlations and their role in children's concepts.

Recent accounts of conceptual development have emphasized the important role intuitive theories play in concept formation; however, it is still not clear exactly how these theories exert their influence. We present evidence that elementary school age children use theories to link together specific features associated with individual concepts. The results of our first experiment indicate that theory-based correlations play a prominent role in typicality judgments and in decisions about category membership. In a second experiment, we demonstrate that children's theories play an important role in determining which attributes will be considered most central to the concept. The results of these studies suggest that feature correlations can serve to link children's concepts with their intuitive theories of the world.

Child↗

PubMed1991

The development of perceived structure and attention: evidence from divided and selective attention tasks.

Three experiments provide converging evidence for the view that both perceived structure and attention change during the elementary school years. Kindergarteners, second graders, and adults performed three speeded tasks: divided attention to conjunctions of features, selective attention to orthogonal dimensions and selective attention to correlated dimensions. The tasks were performed with sizes and shapes that were either spatially integrated or spatially separated. In the divided attention task, conjunctions were identified as quickly as single features with integrated stimuli at all ages, but conjunctions were identified more slowly than single features with separated stimuli by all age group. In the orthogonal dimensions task, interference was observed with integrated stimuli across ages, but the interference in adult performance was asymmetric. With separated stimuli, interference was gradually eliminated with increasing age. In correlated dimensions tasks, younger children showed a redundancy gain with integrated stimuli, but no gain was observed in the performances of the older subjects. With separated stimuli there was no redundancy gain at any age. These results were interpreted to mean that integrated stimuli are initially perceived as wholes by all subjects, but that features become more accessible with increasing age. Even so, attention remains constrained by stimulus structure. In contrast, separated stimuli are initially perceived as features at all ages, and the improvement in performance with increasing age is attributable to the increasing command of attentional resources that accompanies development. Our discussion of these findings focuses on three issues: multiple trends in perceptual development, the characteristics of an adequate theory of perceptual representation and processing, and a comparison of the separability hypothesis and other developmental accounts of perceptual development.

Adult↗

PubMed1990

Event-related potentials and the phonological matching of picture names.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes while subjects determined whether a pair of sequentially presented pictures had rhyming or nonrhyming names. During the 1.56-sec interval between the two pictures, the slow ERP wave recorded over the left hemisphere was more negative-going than that over the right, especially at frontal electrodes. The ERPs evoked by the second picture differed as a function of whether its name rhymed with its predecessor. This difference, taking the form of increased negativity in ERPs to nonrhyming items, had an earlier onset and a greater magnitude at right than at left hemisphere electrodes. This pattern of ERP asymmetries is qualitatively similar to that found when words are rhyme-matched. It is therefore concluded that such asymmetries do not depend on the employment of orthographic material and may reflect some aspect(s) of the phonological processing of visually presented material.

Adolescent↗

PubMed1990

Event-related potentials and the semantic matching of pictures.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes while subjects determined whether pairs of sequentially presented pictures were semantically associated. The ERPs evoked by the second picture of each pair differed as a consequence of whether it was associated with its predecessor, such that ERPs to nonassociated pictures were more negative-going than those to associated items. These differences resulted from the modulation of two ERP components, one frontally distributed and centered on an N300 deflection, the other distributed more widely over the scalp and encompassing an N450 deflection. The modulation of N450 is interpreted as further evidence that the "N400" ERP component is sensitive to semantic relationships between nonverbal stimuli. The earlier N300 effects, which do not appear to occur when ERPs are evoked by semantically primed and unprimed words, could suggest that the semantic processing of pictorial stimuli involves neural systems different from those associated with the semantic processing of words.

Adolescent↗

PubMed1989

Asymmetries in event-related potentials during rhyme-matching: confirmation of the null effects of handedness.

Event-related potentials (ERPs) were recorded from 16 right- and 16 left-handed subjects during two variants of a sequential rhyme-judgement task. These variants manipulated the demands placed on short-term memory, by requiring subjects to match a word either with one or with three previously presented words. In both tasks, ERPs exhibited two lateral asymmetries: (i) during the interval prior to the final word, the CNV was more negative over the left hemisphere, and (ii) rhyme/non-rhyme differences in the amplitude of the N450 component of the ERPs to the final word were larger over the right than the left hemisphere. Neither of these asymmetries was smaller or more variable in left- than in right-handed subjects. It is suggested that these data may indicate that some aspects of language processing are, irrespective of handedness, relatively invariant in the direction and degree of their cerebral lateralization.

Adult↗

PubMed1989

Event-related potentials and the semantic matching of faces.

Event-related brain potentials (ERPs) were recorded while subjects determined whether two sequentially presented famous faces depicted individuals belonging to the same or to different occupational categories. During the 1.56 sec interval between the onset of the faces, ERPs recorded from right hemisphere electrodes were more negative-going than those from electrodes over the left hemisphere. The ERPs evoked by the second face on each trial differed as a consequence of whether or not the person depicted belonged to the occupational category specified by the first face. This difference took the form of a bilaterally-distributed negative-going shift in the ERPs evoked by non-matching as opposed to matching faces. This negativity was maximal around 450 msec post-stimulus. The ERP asymmetries during the inter-stimulus interval are interpreted as evidence for the engagement of cognitive processes lateralized to the right hemisphere. The match/non-match differences are considered to reflect the modulation of an "N400" component similar to that evoked by words, and thus suggest that such components can be modulated by associative priming between non-linguistic stimuli.

Adult↗

PubMed1988

Developmental changes in attentional skills: the effect of irrelevant variations on encoding and response selection.

The present experiments examine how irrelevant variations within a stimulus set interfere with performance in a selective attention task. Second graders, fifth graders, and adults were administered a discrete trial version of a selective attention task in which they were required to search for an object that matched the prime on the targeted dimension. The stimuli in the first experiment were constructed from spatially integrated dimensions whereas the second experiment used spatially separated dimensions. The results indicated that while the spatially separated dimensions were perceived independently by all age groups, developmental differences in perceived structure were evident with the spatially integrated dimensions. Problems associated with response selection were a major source of interference with both types of stimuli, but the severity of the interference varied with the age of the perceiver and the nature of the stimuli. The developmental implications of these findings were considered.

Adult↗

PubMed1988

Event-related potentials and the matching of familiar and unfamiliar faces.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral sites while subjects made same/different judgements on sequentially presented pairs of familiar or unfamiliar faces. During the interval between the first and second face, a slow wave was more negative-going over the right than the left hemisphere, particularly when the faces were familiar. Following the second face, two regions of the waveforms were more negative-going when this face did not match the identity of its predecessor. In the early region (less than 160 msec), this effect was confined to posterior electrode sites and familiar faces. In the later region (greater than 250 msec), the match/non-match effect was widespread across the scalp and was evident for both familiar and non-familiar faces, although in the latency range 350-450 msec (encompassing the "N400" component), it was greater in magnitude in the case of familiar stimuli. It is suggested that the slow wave asymmetries reflect the engagement of short-term memory mechanisms lateralized to the right hemisphere. The match/non-match differences are thought to reflect multiple processes, including the modulation of the "N400" component. The sensitivity of this component to the familiarity manipulation is consistent with the hypothesis that the amplitude of N400 reflects an item's compatibility with currently activated memory representations.

Adult↗

PubMed1987

The development of selective attention: holistic perception versus resource allocation.

In two experiments, a speeded sorting task was administered to children. In each sorting, the child was instructed to sort a deck of cards according to values on one dimension while the values of a second irrelevant dimension were held constant, were correlated, or were varied orthogonally. Experiment 1 evaluated developmental changes in perceived structure as compared with such changes in the control of attention. Different groups of kindergarten, 2d-, and 5th-grade children performed the task with spatially integrated vs spatially separated dimensions. The results indicate that with spatially integrated dimensions there is a trend from holistic to featural perception and an increase in attentional control with increasing age. Spatially separate dimensions are perceived dimensionally at all ages, but show a trend in attentional development. In Experiment 2, the spatially integrated dimensions of Experiment 1 were made separable by portraying different targets within a configuration in different colors. The theoretical implications of the results are discussed.

Attention↗

PubMed1987

Event-related potentials and the interaction between orthographic and phonological information in a rhyme-judgment task.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes in three experiments involving a rhyme-judgment task. Experiment 1 employed sequentially presented word pairs consisting of orthographically similar and dissimilar rhyming and nonrhyming items (RUNG-SUNG, MAKE-ACHE, BEAD-DEAD, GIFT-ROAD). Comparison of the ERPs elicited by the dissimilar pairs revealed a rhyme/nonrhyme difference in the form of an increase in the amplitude of a late negative component (N450) for nonrhyming pairs; this effect was confined almost entirely to right-hemisphere electrodes. By contrast, rhyme/nonrhyme differences in the ERPs to orthographically similar word pairs were smaller in magnitude, later in onset, and bilaterally distributed. Experiment 2 showed that this pattern of ERP effects with orthographically similar items depended upon orthographic and not visual similarity. Experiment 3 tested the hypothesis that the lack of a right-hemisphere based N450 effect with orthographically similar items resulted from the operation of an orthographic priming mechanism. ERPs to nonrhyming pairs containing a word with an inconsistent segment (COAST-FROST) were compared with visually matched controls (SPARSE-CREASE). The rhyme/nonrhyme differences in the N450 components from these two conditions were indistinguishable, although subjects found it as difficult to make nonrhyme responses to "COAST-FROST" pairs as to the orthographically similar nonrhyming items in Experiment 1. It was concluded that while "orthographic priming" accounted for the behavioral data from these experiments, it could not explain the interaction between phonology and orthography observed in the concurrently recorded ERP data.

Adolescent↗