Search PubMed⌕ Search

Biomedical subjects

L B Smith

Publications and source records attributed to L B Smith.

At least 37 records · Page 2Linked to original sources
PubMed1997

A curvilinear trend in naming errors as a function of early vocabulary growth.

This research examines changes in word retrieval and naming during a developmental period in which there is a substantial increase in productive vocabulary. That increase generally occurs when children have between 50 to 150 words in productive vocabulary. We examined children's naming errors in two studies for what these errors could tell us about the emerging lexicon. The method we used for eliciting spontaneous naming was picture book reading by the parent. In Experiment 1, 12 children were followed longitudinally at three-week intervals from 15 to 22 months. Parent diaries were used as a measure of vocabulary growth. Experiment 2 used a cross-sectional design to compare the naming errors of 60 children assigned to one of three vocabulary ranges. Measures of vocabulary size were based on the MacArthur Communicative Development Inventory. In both experiments we found a sharp increase in naming errors in the picture book task that was coincident with sudden changes in productive vocabulary. These naming errors were often perseverative in nature and appear to reflect interference in the retrieval process from previously retrieved words. The results suggest that these errors in naming are a consequence of changes in lexical processing that occur with rapid growth of productive vocabulary and concurrent increased rates of speaking.

Analysis of Variance↗
PubMed1997

Cognition and communication: referential strategies used by preschoolers with specific language impairment.

Ten children with specific language impairment and 10 children with normal language development were asked to describe objects so that a listener could select them. Each trial targeted two out of a group of three toys. The targeted objects were identical or were similar in size or color. Children in the two groups did not differ in referential success, although children in both groups found the size items more difficult. Content analysis of the messages did reveal differences in the referential strategies used most frequently. Children with specific language impairment were more likely to mention the attributes of each object separately, rather than to describe the characteristics common to a pair of objects. Children in both groups talked about separate objects more often when talking about size than about color or object type. Use of this strategy could indicate the effects of attentional capacity on children's solutions to communication tasks.

Child, Preschool↗
PubMed1997

Effect of chronic low-level exposure to jet fuel on postural balance of US Air Force personnel.

This study used the postural stability technique to investigate the neurological effects of cumulative low-level exposure to raw JP-8 jet fuel vapor on aircraft maintenance personnel. All subjects performed two sets of four 30-second postural sway tests. The results of mean cumulative exposure levels (in parts per million +/- standard error of mean) were the following: naphthas, 1308 +/- 292; benzene, 21.2 +/- 5.7; toluene, 23.8 +/- 6.1; and m-,o-, p-xylene, 22.7 +/- 5.4. Covariate adjusted regression analysis of the exposed group data showed a statistically significant association (P < 0.05) between the solvents (benzene, toluene, and xylene) and increased postural sway response. For all solvent exposures, the "eyes closed, on foam" test provided the strongest association between sway length and JP-8 benzene (r2 range, 0.45 to 0.52), implying subtle influence on vestibular/proprioception functionalities.

Adult↗
PubMed1996

A complete genome screen for genes predisposing to severe bipolar disorder in two Costa Rican pedigrees.

Bipolar mood disorder (BP) is a debilitating syndrome characterized by episodes of mania and depression. We designed a multistage study to detect all major loci predisposing to severe BP (termed BP-I) in two pedigrees drawn from the Central Valley of Costa Rica, where the population is largely descended from a few founders in the 16th-18th centuries. We considered only individuals with BP-I as affected and screened the genome for linkage with 473 microsatellite markers. We used a model for linkage analysis that incorporated a high phenocopy rate and a conservative estimate of penetrance. Our goal in this study was not to establish definitive linkage but rather to detect all regions possibly harboring major genes for BP-I in these pedigrees. To facilitate this aim, we evaluated the degree to which markers that were informative in our data set provided coverage of each genome region; we estimate that at least 94% of the genome has been covered, at a predesignated threshold determined through prior linkage simulation analyses. We report here the results of our genome screen for BP-I loci and indicate several regions that merit further study, including segments in 18q, 18p, and 11p, in which suggestive lod scores were observed for two or more contiguous markers. Isolated lod scores that exceeded our thresholds in one or both families also occurred on chromosomes 1, 2, 3, 4, 5, 7, 13, 15, 16, and 17. Interesting regions highlighted in this genome screen will be followed up using linkage disequilibrium (LD) methods.

Bipolar Disorder↗
PubMed1996

Use of linkage disequilibrium approaches to map genes for bipolar disorder in the Costa Rican population.

Linkage disequilibrium (LD) analysis provides a powerful means for screening the genome to map the location of disease genes, such as those for bipolar disorder (BP). As described in this paper, the population of the Central Valley of Costa Rica, which is descended from a small number of founders, should be suitable for LD mapping; this assertion is supported by reconstruction of extended haplotypes shared by distantly related individuals in this population suffering low-frequency hearing loss (LFHL1), which has previously been mapped by linkage analysis. A sampling strategy is described for applying LD methods to map genes for BP, and clinical and demographic characteristics of an initially collected sample are discussed. This sample will provide a complement to a previously collected set of Costa Rican BP families which is under investigation using standard linkage analysis.

Adult↗
PubMed1996

Naming in young children: a dumb attentional mechanism?

Previous studies have shown that young children selectively attend to some object properties and ignore others when generalizing a newly learned object name. Moreover, the specific properties children attend to depend on the stimulus and task context. The present study tested an attentional account: that children's feature selection in name generalization is guided by non-strategic attentional processes that are minimally influenced by new conceptual information presented in the task. Four experiments presented 3-year-old children and adults with novel artifacts consisting of distinctive base objects with appended parts. In a Name condition, subjects were asked whether test objects had the same name as the exemplar. In a Similarity condition, subjects made similarity judgments for the same objects. Subjects in two experiments were shown a function for either the base object or the parts. Both adults' naming and similarity judgments were influenced by the functional information. Children's similarity judgments were also influenced by the functions. However, children's naming was immune to influence from information about function. Instead, children's feature selection in naming was shifted only by changes in the relative salience of base objects and parts. The results are consistent with the idea that dumb attentional processes are responsible for young children's smart generalizations of novel words to new instances. Potential mechanisms to explain these findings are discussed.

Adult↗
PubMed1996

Genetic mapping using haplotype, association and linkage methods suggests a locus for severe bipolar disorder (BPI) at 18q22-q23.

Manic depressive illness, or bipolar disorder (BP), is characterized by episodes of elevated mood (mania) and depression. We designed a multistage study in the genetically isolated population of the Central Valley of Costa Rica to identify genes that promote susceptibility to severe BP (termed BPI), and screened the genome ot two Costa Rican BPI pedigrees (McInnes et al., submitted). We considered only individuals who fulfilled very stringent diagnostic criteria for BPI to be affected. The strongest evidence for a BPI locus was observed in 18q22-q23. We tested 16 additional markers in this region and seven yielded peak lod scores over 1.0. These suggestive lod scores were obtained over a far greater chromosomal length (about 40 cM) than in any other genome region. This localization is supported by marker haplotypes shared by 23 of 26 BPI affected individuals studied. Additionally, marker allele frequencies over portions of this region are significantly different in the patient sample from those of the general Costa Rican population. Finally, we performed an analysis which made use of both the evidence for linkage and for association in 18q23, and we observed significant lod scores for two markers in this region.

Alleles↗
PubMed1996

Attitudes towards bipolar disorder and predictive genetic testing among patients and providers.

Attitudes about bipolar disorder (manic depressive disorder) and genetic testing were investigated. Three groups of subjects were surveyed including members of a manic depressive support group, medical students, and psychiatry residents. The questionnaire was intended to elicit impressions and attitudes about bipolar disorder (BP) from mental health consumers and health care providers with varying levels of personal and professional familiarity with the disorder. Attitudes towards prenatal testing and pregnancy termination were also assessed. The intention hypothetically to terminate a pregnancy was influenced by the likelihood of developing BP a well as the projected course and severity of illness. Nearly half of the total sample would terminate pregnancy if the fetus were definitely to develop an unspecified form of bipolar disorder. Presumed severity of illness was also found to be a modifying factor in the decision, with a low percentage of subjects electing to terminate for a mild course of bipolar disorder and a majority opting for termination in the case of an extremely severe presentation. Support group members were the least likely to terminate a hypothetical pregnancy in the case of a positive prenatal test and were the most likely to desire childhood testing in the absence of preventive or treatment options. The possible implications of these findings, as well as avenues of future research, are discussed.

Abortion, Spontaneous↗
PubMed1992

A developmental analysis of the polar structure of dimensions.

Some dimensions such as size and loudness are clearly marked for magnitude with one end being "more than" the other end. Thus, big is more than little and loud is more than quiet. This research examined the interaction of perception and language in the development of the magnitude marking of size, loudness, and achromatic color. Children 2 to 5 years of age and adults participated in six experiments. A cross-dimension matching task and a "Which is more?" task were used. The results suggest fast, invariant, and unidirectional development for size and loudness. Big is perceptually and linguistically more than little early in development and becomes more strongly organized with development. Loudness starts out disorganized and may be linguistically organized into more and less ends before it is perceptually organized. However, developments in perception and in language are rapid and in the same direction. In contrast, achromatic color shows an irregular developmental trend. Early in development, dark grey is perceptually more than light grey. But this early organization is disrupted at the same time that children acquire the words dark and light. The results suggest converging interactions between perception and language in the case of size and loudness and antagonistic interactions in the case of darkness. The results are interpreted in terms of a dynamical system.

Child, Preschool↗
PubMed1992

Kawasaki syndrome.

Explore the source record for details and available documents.

Arthritis, Rheumatoid↗
PubMed1991

Classifying by dimensions and reading: a comparison of the auditory and visual modalities.

Children have difficulty learning to read alphabetic writing systems, in part, because they have difficulty segmenting spoken language into phonemes. Young children also have difficulty attending to the individual dimensions of visual objects. Thus, children's early difficulty in reading may be one sign of a general inability to selectively attend to the parts of any perceptual wholes. To explore this notion, children in kindergarten through fourth grade (Experiments 1, 3, and 4) and adults (Experiment 2) classified triads of spoken syllables and triads of visual objects. Classifying speech by common parts was positively related to reading and spelling ability (Experiments 1 and 4), but usually not to classifying visual stimuli by common parts under free classification instructions (Experiments 1 through 3). However, classification was more consistent across the visual and auditory modalities when the children were told to classify based on a shared constituent (Experiment 4). Regardless of instructions, performance on the visual tasks did not usually relate to reading and spelling skill. The ability to attend selectively to phonemes seems to be a "special" skill--one which may require specific experiences with language, such as those involved in learning to read an alphabetic writing system.

Attention↗
PubMed1991

Object properties and knowledge in early lexical learning.

The ease with which young children learn object nouns suggests that they possess strategies to identify properties critical to lexical category membership. In previous work, young children used a same-shape criterion to extend new count nouns. The present research tested the generality of this shape bias. 2- and 3-year-olds were asked either to extend a novel count noun to new instances, or to choose unnamed objects to go together. The objects varied in shape, size, and texture. For half of the subjects, the objects had eyes--a property strongly associated with certain material kinds. If young children know this association, they should attend to texture as well as shape in classifying objects with eyes. With named objects only, both 2- and 3-year-old children classified eyeless objects by shape and objects with eyes by both shape and texture. The results suggest that very young children possess considerable knowledge about conditional relations between kinds of perceptual properties. Knowledge of such conditional relations may aid children in forming new categories and thus in discovering new word meanings.

Attention↗
PubMed1990

New evidence on the development of the word big.

Previous studies of children's understanding of big suggest a curvilinear trend. 3-year-olds, like adults, interpret big as referring to area, while 5-year-olds take big to mean tall. The results of 6 experiments indicate that the curvilinear trend is not obtained in all stimulus contexts. When objects vary extremely, younger and older children take big to mean tall. The object to which big is applied also influences whether height, length, or area is attended to. Moreover, in a production task, adults rarely used the work big to describe the stimuli with which children's understanding of big is typically tested. Taken together, the results suggest that the meaning and use of big is complex and that big may not at any age refer simply to the larger object. It is proposed that the meaning of big is a dynamic system driven by a multiple of perceptual, conceptual, and semantic influences.

Adult↗
PubMed1989

A model of perceptual classification in children and adults.

The developmental trend from overall-similarity to dimensional-identity classifications is explained by a quantitative model. I begin with the assumption that objects are represented in terms of constituent dimensions and that the representation of objects changes little with development. Given this assumption, the model has three major parts. First, the similarity between objects is a function of the combination of the constituent dimensional differences. I propose developmental change in the likelihood that dimensions are differentially weighted in the calculation of similarity. Second, the perceived similarities between objects are valued for the purpose of constructing classifications. I propose that similarities are valued more dichotomously with age, such that identity becomes increasingly special. Third, the valued similarities are used to choose the best classification of those possible. The model provides good qualitative fits to the extant data. Three experiments examining classifications in 2- to 8-year-olds and in adults support specific new claims of the model. The data and the model provide new insights about development, classification, and similarity.

Adult↗
PubMed1989

Dimensional thinking in language impaired children.

This study investigated the dimensional knowledge evidenced by language impaired (LI) preschoolers. Ten LI and 10 language normal (LN) children, aged 3:6 to 5:9, were asked to solve verbal and nonverbal problems requiring color and size judgments. There were no group differences on the verbal task, but the LI children performed less well than the LN children on the nonverbal task. Much of this difference stemmed from their difficulty with size items. The ordinal nature of the size dimension implies greater cognitive processing demands than are inherent in nominal dimensions such as color. Given the known processing limitations of language impaired children, this complexity apparently can lead to erroneous judgment even when requisite knowledge is present. It may also contribute to delays in the initial construction of dimensional knowledge.

Child, Preschool↗