Biomedical subjects

L B Smith

Publications and source records attributed to L B Smith.

At least 19 recordsLinked to original sources

PubMed2006

Enhanced skeletal growth of sheep heterozygous for an inactivated fibroblast growth factor receptor 3.

Normal fibroblast growth factor receptor 3 (FGFR3) acts as a negative bone growth regulator by restricting chondrocyte proliferation and endochondral bone elongation. In sheep, a heritable mutation that inactivates FGFR3 produces skeletal overgrowth when homozygous, this condition is commonly referred to as spider lamb syndrome (SLS). We hypothesized that sheep heterozygous for the inactivated FGFR3 mutation (FGFR3(SLS/+)) would exhibit enhanced long bone growth and greater frame size; additionally, the isolated effects of increased bone growth would translate into greater BW and larger LM area relative to normal lambs at harvest. The current study investigated bone length and LM area of FGFR3(SLS/+) sheep at maturity and during growth. At maturity, FGFR3(SLS/+) ewes exhibited a larger frame size and longer bones than normal FGFR3(+/+) ewes (P < 0.05). Similarly, FGFR3(SLS/+) lambs had greater frame sizes than normal FGFR3(+/+) lambs, as indicated by increased metacarpal III length and height at withers (P < 0.05). The FGFR3(SLS/+) lambs took longer than the normal FGFR3(+/+) lambs to reach the 60-kg common BW harvest end point (P < 0.05). The FGFR3(SLS/+) lambs showed no difference in BW, ADG, or LM area at any age compared with normal FGFR3(+/+) lambs (P > 0.2). A similar LM area produced in the context of a greater frame size and skeletal length produces a greater muscle volume, thereby potentially increasing meat yield. The results of this study suggest that FGFR3(SLS/+) animals exhibit a relaxation of the normal inhibition of chondrocyte proliferation, resulting in an increase in the overall frame size. The sheep industry could utilize the naturally occurring genetic mutation in FGFR3 to potentially increase meat yields with enhanced skeletal growth as an alternative to exogenous growth promotants.

Aging↗

PubMed2004

Dissociation of body growth and adipose deposition effects of growth hormone in oMt1a-oGH transgenic mice.

Chronic highly elevated expression of a growth hormone (GH) transgene enhances overall body growth with minimal adipose accretion, while moderate levels of circulating GH fail to enhance body growth yet promote adipose deposition. These findings suggest that the growth response to GH can be dissociated from adipose effects. This hypothesis was tested in the oMtla-oGH transgenic mouse model by titrating circulating GH levels through variable induction of transgene expression. Circulating GH levels in female transgenics were approximately 49, 132, and 750 ng/ml in response to the transgene stimulus at 0, 15, and 25 mM zinc sulfate, respectively. The highest level of circulating GH generated the largest body weight with the smallest fat accrual while the intermediate GH level generated a body weight equivalent to that for the highest GH but the heaviest gonadal fat pads. The lowest GH levels did not increase body size but did enlarge fat depots. Animals exposed to the highest level of GH had an extended growth phase relative to lower GH levels and the nontransgenic controls. In contrast, the duration of the growth phase for the 0 and 15 mM zinc stimulated transgenics was abbreviated relative to the growth phase of the control animals. The two highest levels of circulating GH increased all forms of the GH receptor, IGF-I, and hepatic lipoprotein lipase mRNA. The growth differential observed for the 0 vs. the 15 mM zinc stimulated transgenics may reflect the preferential increase in the full length GH receptor mRNA and the induction of the smaller IGF-I transcripts with the higher circulating GH while the lipid accrual paralleled the disproportionate induction of the truncated GH receptor mRNA form. Liver and bone content of zinc, manganese, copper, and iron primarily reflected dietary zinc supplementation and did not appear to play a role in the differential growth response. The dissociation of GH effects on growth and adipogenesis as a function of circulating GH levels suggests that the level of GHR and IGF-I expression acts through a threshold mechanism and low expression results in adipogenesis while high expression generates body growth.

Adipose Tissue↗

PubMed2001

The role of target distinctiveness in infant perseverative reaching.

From a dynamic systems perspective, perseverative errors in infancy arise from the interaction of the perceptual cues with the memory of previous actions. To evaluate this account, we tested 9-month-old infants in a task in which they reached for two targets. Experimenters repeatedly cued the first target, which always matched the background (A), and then cued the second target, which varied in its distinctiveness (B). We predicted that a sufficiently distinctive B target would lessen perseverative responding. Results showed that infants perseverated when reaching for two identical targets, but that they made nonperseverative responses when reaching in the presence of a highly distinctive B target. Reach direction on each trial was jointly determined by the distinctiveness of the target, the immediately preceding perceptual events, and the history of reaches in the task.

Child Development↗

PubMed2001

Early noun lexicons in English and Japanese.

Previous research suggests that children learning a variety of languages acquire similar early noun vocabularies and do so by similar and universal processes. We report here results from two studies that show differences in the early noun learning of English- and Japanese-speaking children. Experiment 1 examined the relative numbers of animal names and object names in vocabularies of English-speaking and Japanese-speaking children. English-speaking children's vocabularies were heavily lopsided with many more object than animal names whereas Japanese-speaking children's vocabularies were more evenly balanced. Experiment 2 used a novel noun extension task to examine what young children know about the different organizations of animal and artifact categories. The results suggest that early learners of English but not Japanese over-generalize what they know about object categories to animal categories. The role of culture, input and linguistic structure in early noun acquisitions is discussed.

Analysis of Variance↗

PubMed2001

The dynamics of embodiment: a field theory of infant perseverative reaching.

The overall goal of this target article is to demonstrate a mechanism for an embodied cognition. The particular vehicle is a much-studied, but still widely debated phenomenon seen in 7-12 month-old-infants. In Piaget's classic "A-not-B error," infants who have successfully uncovered a toy at location "A" continue to reach to that location even after they watch the toy hidden in a nearby location "B." Here, we question the traditional explanations of the error as an indicator of infants' concepts of objects or other static mental structures. Instead, we demonstrate that the A-not-B error and its previously puzzling contextual variations can be understood by the coupled dynamics of the ordinary processes of goal-directed actions: looking, planning, reaching, and remembering. We offer a formal dynamic theory and model based on cognitive embodiment that both simulates the known A-not-B effects and offers novel predictions that match new experimental results. The demonstration supports an embodied view by casting the mental events involved in perception, planning, deciding, and remembering in the same analogic dynamic language as that used to describe bodily movement, so that they may be continuously meshed. We maintain that this mesh is a pre-eminently cognitive act of "knowing" not only in infancy but also in everyday activities throughout the life span.

Child Development↗

PubMed2001

Why children learn color and size words so differently: evidence from adults' learning of artificial terms.

An adult simulation study examined why children's learning of color and size terms follow different developmental patterns, one in which word comprehension precedes success in nonlinguistic matching tasks versus one in which matching precedes word comprehension. In 4 experiments, adults learned artificial labels for values on novel dimensions. Training mimicked that characteristic for children learning either color words or size words. The results suggest that the learning trajectories arise from the different frames in which different dimensions are trained: Using a comparison (size-like) training regimen helps learners pick out the relevant dimension, and using a categorization (color-like) training regimen helps the learner correctly comprehend and produce dimension terms. The results indicate that the training regimen, not the meanings of the terms or the specific dimensions, determines the pattern of learning.

Adult↗

PubMed2001

Contrasting genome organisation: two regions of the Brassica oleracea genome compared with collinear regions of the Arabidopsis thaliana genome.

Brassica crop species are of worldwide importance and are closely related to the model plant Arabidopsis thaliana for which the complete genome sequence has recently been established. We investigated collinearity of marker order by comparing two contrasting regions of the Brassica oleracea genome with homologous regions of A. thaliana. Although there is widespread replication of marker loci in both A. thaliana and B. oleracea, we found that a combination of genetic markers mapped in B. oleracea, including RFLPs, CAPS, and SSRs allowed comparison and interpretation of medium-scale chromosomal organisation and rearrangements. The interpretation of data was facilitated by hybridising probes onto the whole A. thaliana genome, as represented by BAC contigs. Twenty marker loci were sampled from the whole length of the shortest B. oleracea linkage group, 06, and 21 from a 30.4-cM section of the longest linkage group, 03. There is evidence of locus duplication on linkage group 06. Locus order is well conserved between a putative duplicated region of 10.5 cM and a discrete region comprising 25 cM of A. thaliana chromosome I. This was supported by evidence from seven paralogous loci, three of which were duplicated in a 30.6-cM region of linkage group 06. The pattern of locus order for the remainder of linkage group 06 and the sampled section of linkage group 03 was more complex when compared with the A. thaliana genome. Although there was some conservation of locus order between markers on linkage group 03 and approximately 9 cM of A. thaliana chromosome I, this was superimposed upon a complex pattern of additional loci that were replicated in both A. thaliana and B. oleracea. The results are discussed in the context of the ability to use collinear information to assist map-based cloning.

Arabidopsis↗

PubMed2000

Counting nouns and verbs in the input: differential frequencies, different kinds of learning?

Previous research has focused on evaluating the nouns and verbs in parents' input through type/token ratios. This research offers an additional means of evaluating parent speech by first examining the frequencies of individual nouns, verbs and descriptors and second examining the learning task presented to children. Study 1 examines 25 transcripts from the CHILDES database of English-speaking parents' speech to children at five developmental levels ranging from 0;11 to 2;11 in age. Study 2 examines 50 transcripts from the CHILDES database of Mandarin-speaking caregivers' speech to children ranging from 1;9 to 2;3 in age. The results suggest that the patterns of frequency for individual nouns and individual verbs are different, but that the frequency patterns for nouns and the frequency patterns for verbs are similar in English and Mandarin. Further, this research suggests that in both languages the nouns in parents' input are similarly organized: the most frequent nouns spoken to children tend to name solid objects that share a similar shape. In contrast verbs' meanings in both languages tend to include more variable conceptual relations.

Child Language↗

PubMed2000

Adults' acquisition of novel dimension words: creating a semantic congruity effect.

The semantic congruity effect is exhibited when adults are asked to compare pairs of items from a series, and their response is faster when the direction of the comparison coincides with the location of the stimuli in the series. For example, people are faster at picking the bigger of 2 big items than the littler of 2 big items. In the 4 experiments presented, adults were taught new dimensional adjectives (mal/ler and borg/er). Characteristics of the learning situation, such as the nature of the stimulus series and the relative frequency of labeling, were varied. Results revealed that the participants who learned the relative meaning of the artificial dimensional adjectives also formed categories and developed a semantic congruity effect regardless of the characteristics of training. These findings have important implications for our understanding of adult acquisition of novel relational words, the relationship between learning such words and categorization, and the explanations of the semantic congruity effect.

Adult↗

PubMed2000

Exposures to jet fuel and benzene during aircraft fuel tank repair in the U.S. Air Force.

Jet fuel and benzene vapor exposures were measured during aircraft fuel tank entry and repair at twelve U.S. Air Force bases. Breathing zone samples were collected on the fuel workers who performed the repair. In addition, instantaneous samples were taken at various points during the procedures with SUMMA canisters and subsequent analysis by mass spectrometry. The highest eight-hour time-weighted average (TWA) fuel exposure found was 1304 mg/m3; the highest 15-minute short-term exposure was 10,295 mg/m3. The results indicate workers who repair fuel tanks containing explosion suppression foam have a significantly higher exposure to jet fuel as compared to workers who repair tanks without foam (p < 0.001). It is assumed these elevations result from the tendency for fuel, absorbed by the foam, to volatilize during the foam removal process. Fuel tanks that allow flow-through ventilation during repair resulted in lower exposures compared to those tanks that have only one access port and, as a result, cannot be ventilated efficiently. The instantaneous sampling results confirm that benzene exposures occur during fuel tank repair; levels up to 49.1 mg/m3 were found inside the tanks during the repairs. As with jet fuel, these elevated benzene concentrations were more likely to occur in foamed tanks. The high temperatures associated with fuel tank repair, along with the requirement to wear vapor-permeable cotton coveralls for fire reasons, could result in an increase in the benzene body burden of tank entrants.

Air Pollutants, Occupational↗

PubMed2000

Personal exposure to JP-8 jet fuel vapors and exhaust at air force bases.

JP-8 jet fuel (similar to commercial/international jet A-1 fuel) is the standard military fuel for all types of vehicles, including the U.S. Air Force aircraft inventory. As such, JP-8 presents the most common chemical exposure in the Air Force, particularly for flight and ground crew personnel during preflight operations and for maintenance personnel performing routine tasks. Personal exposure at an Air Force base occurs through occupational exposure for personnel involved with fuel and aircraft handling and/or through incidental exposure, primarily through inhalation of ambient fuel vapors. Because JP-8 is less volatile than its predecessor fuel (JP-4), contact with liquid fuel on skin and clothing may result in prolonged exposure. The slowly evaporating JP-8 fuel tends to linger on exposed personnel during their interaction with their previously unexposed colleagues. To begin to assess the relative exposures, we made ambient air measurements and used recently developed methods for collecting exhaled breath in special containers. We then analyzed for certain volatile marker compounds for JP-8, as well as for some aromatic hydrocarbons (especially benzene) that are related to long-term health risks. Ambient samples were collected by using compact, battery-operated, personal whole-air samplers that have recently been developed as commercial products; breath samples were collected using our single-breath canister method that uses 1-L canisters fitted with valves and small disposable breathing tubes. We collected breath samples from various groups of Air Force personnel and found a demonstrable JP-8 exposure for all subjects, ranging from slight elevations as compared to a control cohort to > 100 [mutilpe] the control values. This work suggests that further studies should be performed on specific issues to obtain pertinent exposure data. The data can be applied to assessments of health outcomes and to recommendations for changes in the use of personal protective equipment that optimize risk reduction without undue impact on a mission.

Air Pollutants, Occupational↗

PubMed2000

Real-time and integrated measurement of potential human exposure to particle-bound polycyclic aromatic hydrocarbons (PAHs) from aircraft exhaust.

We used real-time monitors and low-volume air samplers to measure the potential human exposure to airborne polycyclic aromatic hydrocarbon (PAH) concentrations during various flight-related and ground-support activities of C-130H aircraft at an Air National Guard base. We used three types of photoelectric aerosol sensors (PASs) to measure real-time concentrations of particle-bound PAHs in a break room, downwind from a C-130H aircraft during a four-engine run-up test, in a maintenance hangar, in a C-130H aircraft cargo bay during cargo-drop training, downwind from aerospace ground equipment (AGE), and in a C-130H aircraft cargo bay during engine running on/off (ERO) loading and backup exercises. Two low-volume air samplers were collocated with the real-time monitors for all monitoring events except those in the break room and during in-flight activities. Total PAH concentrations in the integrated-air samples followed a general trend: downwind from two AGE units > ERO-loading exercise > four-engine run-up test > maintenance hangar during taxi and takeoff > background measurements in maintenance hangar. Each PAH profile was dominated by naphthalene, the alkyl-substituted naphthalenes, and other PAHs expected to be in the vapor phase. We also found particle-bound PAHs, such as fluoranthene, pyrene, and benzo[a]pyrene in some of the sample extracts. During flight-related exercises, total PAH concentrations in the integrated-air samples were 10-25 times higher than those commonly found in ambient air. Real-time monitor mean responses generally followed the integrated-air sample trends. These monitors provided a semiquantitative temporal profile of ambient PAH concentrations and showed that PAH concentrations can fluctuate rapidly from a baseline level < 20 to > 4,000 ng/m(3) during flight-related activities. Small handheld models of the PAS monitors exhibited potential for assessing incidental personal exposure to particle-bound PAHs in engine exhaust and for serving as a real-time dosimeter to indicate when respiratory protection is advisable.

Air Movements↗

PubMed1999

Early noun vocabularies: do ontology, category structure and syntax correspond?

This paper examines children's early noun vocabularies and their interpretations of names for solid and non-solid things. Previous research in this area assumes that ontology, category organization and syntax correspond in the nouns children learn early such that categories of solid things are organized by shape similarity and named with count nouns and categories of non-solid things are organized by material similarity and named with mass nouns. In Experiment 1 we examine the validity of this assumption in a corpus of early-learned nouns and conclude that one side of the solidity-syntax-category organization mapping is favored. In our second experiment we examine the relation between early noun vocabulary development and novel word generalization. We find that children between 17 and 33 months of age do not systematically generalize names for solid things by shape similarity until they already know many nouns, and do not systematically generalize names for non-solid substances by material similarity. The implications for children's acquisition of the ontological distinction, count/mass syntax, and novel nouns are discussed.

Age Factors↗

PubMed1999

Learning color words involves learning a system of mappings.

This research examines the difficulty children encounter when acquiring 2 specific sets of adjectives, color and size words, and suggests that children must acquire a system of mapping in learning these words. Children were assessed on 4 types of mappings (word-word maps, property-property maps, word-property maps, and word-word-property maps) by completing 3 color tasks. Children also participated in comparable tasks for size words. In Study 1, 13 two-year-olds were followed longitudinally at 3-week intervals. In Study 2, 56 two-year-olds participated in a cross-sectional replication. The results indicate that children acquire color maps in a characteristic order. Children demonstrated a different pattern of acquisition for size words. The results suggest that learning word associations may promote color word acquisition and that learning color words may promote selective attention to color.

Attention↗

PubMed1999

Underreporting sensitive behaviors: the case of young women's willingness to report abortion.

Accurate reports are important in health research, yet abortions are underreported in surveys by almost half. This study examined influences on reporting of abortion among adolescents. Participants were 63 young women from varied ethnic backgrounds who had undergone abortions at urban abortion clinics. Participants reported on their willingness to be honest about their abortion in various research settings and in comparison with other sensitive topics. Willingness to report was also examined in relation to the sponsor of the research, the mode of administration, and the characteristics of the interviewer. Adolescents indicated less willingness to report abortion than some behaviors such as cigarette smoking, but they were more willing to report abortion than family income, oral sex, or anal sex. Comparison of willingness to report across research settings indicated that face-to-face interviews appear to generate more accurate reporting than telephone surveys. The implications of these findings for the study of other health behaviors are discussed.

Abortion, Legal↗

PubMed1999

Knowing in the context of acting: the task dynamics of the A-not-B error.

The A-not-B error is one of the most robust and highly studied phenomena in developmental psychology. The traditional Piagetian interpretation is that the error reflects the immaturity of infants' understanding of objects as permanent entities. More recently, the error has been interpreted in terms of changes in representation, in memory, in spatial knowledge, and in inhibitory processes. Each account may be partially right but none offers a unified account of the many accumulated facts about this error. This article presents and tests a new unified explanation. The authors propose that the perseverative reach back to A is the product of the processes that take a hand to a location in visual space: the body-centered nature of the spatial code, memories for previous reaching activity, and the close coupling of looking and reaching. The results from 6 experiments support this explanation. The results are used to challenge the idea of knowledge independent of and distinct from behavior.

Analysis of Variance↗

PubMed1998

Audition and visual attention: the developmental trajectory in deaf and hearing populations.

This study examined the development of visual attention in 5- to 13-year-olds who differed in their access to sound. Hearing children, deaf children with cochlear implants, and deaf children without implants participated in a task in which they were to respond to some visual signals and not others. The results of Experiment I indicated that the timing of developmental changes in visual selective attention was similar for all 3 groups, occurring around 8 years. The magnitude of age-related change differed among groups; hearing children and older deaf children using a cochlear implant reached higher levels of performance with age than did deaf children without enhanced access to sound. The results of Experiment 2 suggest that the developmental differences between deaf children with and without cochlear implants begin prior to 8 years and may be related to their use of environmental sounds to organize visual attention.

Adolescent↗

PubMed1998

Memory and attention make smart word learning: an alternative account of Akhtar, Carpenter, and Tomasello.

Two general types of accounts have been offered to explain the smartness of young children's word learning. One account postulates that children enter the word-learning task with specific knowledge about how words link to categories. The second account puts the source of children's smart word learning in knowledge about the pragmatics of communication and social interactions. The present experiment tested a third idea: that children's seemingly smart word learning derives from general, indeed mundane, cognitive processes. Forty-eight children from 18 to 28 months of age participated in a task designed to test our alternative explanation as applied to Akhtar, Carpenter, and Tomasello's (1996) finding that children use knowledge of the communicative intents of others to interpret a novel noun. Specifically, we suggest that children's attention to the proper referent was guided by the general effects of a contextual shift on memory and attention. The procedure in the present study was identical to that of Akhtar et al. except that we differentiated the target through a nonsocial context shift. Findings similar to that of Akhtar et al. emerged under the present procedures. These results strongly suggest that general attentional and memorial processes, and not knowledge about the communicative intents of others, may guide young children's word learning. These findings provide one demonstration of how smart word learning may emerge from more ordinary (and dumb) cognitive processes.

Attention↗