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Biomedical subjects

R Lawson

Publications and source records attributed to R Lawson.

At least 19 recordsLinked to original sources
PubMed2005

Phylogeny of the Colubroidea (Serpentes): new evidence from mitochondrial and nuclear genes.

The Colubroidea contains over 85% of all the extant species of snakes and is recognized as monophyletic based on morphological and molecular data. Using DNA sequences (cyt b, c-mos) from 100 species we inferred the phylogeny of colubroids with special reference to the largest family, the Colubridae. Tree inference was obtained using Bayesian, likelihood, and parsimony methods. All analyses produced five major groups, the Pareatidae, Viperidae, Homalopsidae, the Elapidae, and the Colubridae. The specific content of the latter two groups has been altered to accommodate evolutionary history and to yield a more stable taxonomy. We propose an updated classification based on the reallocation of species as indicated by our inferred phylogeny.

Animals↗
PubMed2003

Poor response to ovulation induction is a stronger predictor of early menopause than elevated basal FSH: a life table analysis.

BACKGROUND: During the course of assisted reproduction treatment, a number of women exhibit a "poor response" to ovulation induction, or demonstrate an elevated basal FSH level (> or =10 IU/l) at a young age. We sought to determine whether these women are at increased risk of early menopause and poor reproductive performance. METHODS: A retrospective cohort study included 118 "poor responders" with normal basal FSH level (<10 IU/l), 164 women with raised basal FSH (> or =10 IU/l), and 265 controls, who underwent assisted reproduction treatment between 1987 and 1998. All women were < 40 years of age at the time of treatment and had normal menstrual cycles. Participants were sent a postal questionnaire in 2000-2001, seeking information on ovarian function and reproductive performance following cessation of treatment. RESULTS: After adjusting for age and smoking habits, women with poor response and raised basal FSH levels were more likely to experience symptoms of the peri-menopause [hazard ratios 2.4, 95% confidence interval (CI) 1.52-3.78, and 2.76, 95% CI 1.78-4.29 respectively, P = 0.0001]. Poor responders were six times and 23 times more likely to experience the menopause within 10 years of treatment than those with raised basal FSH levels and controls respectively (hazard ratio 5.97 and 23.9, P = 0.015 and 0.002 respectively). Poor responders and those with raised basal FSH levels have half the chance of spontaneous conception after discontinuation of treatment compared with controls (P < 0.007). CONCLUSIONS: Both poor response to ovarian stimulation and raised basal FSH are markers of reduced ovarian reserve and predict an increased risk of early menopause.

Adult↗
PubMed2001

Screening for HIV, hepatitis B and C infection in a population seeking assisted reproduction in an inner London hospital.

The Human Fertilisation and Embryology Authority requires all sperm donors to be screened for human immunodeficiency virus (HIV), hepatitis B and C and their semen quarantined for six months. No guidelines exist for screening prior to in vitro fertilisation or intracytoplasmic sperm injection. We prospectively analysed the prevalence of these viruses in our patients. Screening detected one case of HIV (0.13%), four of hepatitis C (0.5%) and 14 new cases of hepatitis B (1.7%). The prevalence of hepatitis B and HIV in our antenatal population at this time was 1.4% and 0.8%, respectively. Knowledge allows measures to be taken to reduce the risk of transmission to partner, fetus, new born baby, or by cross-contamination during embryo cryostorage and enables couples to make an informed decision regarding proceeding with treatment. Detection of infection in one partner should no longer preclude fertility treatment.

Female↗
PubMed2000

The combined effects of plane disorientation and foreshortening on picture naming: one manipulation or two?

Objects disoriented in plane away from the upright and objects rotated in depth producing foreshortening are harder to identify than canonical views. In Experiments 1 and 2, participants named pictures of familiar objects. There was no interaction between plane and depth rotation effects on initial presentation or after practice. Experiment 3 was a dual-task psychological refractory period study. Participants classified a high-low tone with a speeded keypress and then named a canonical, plane-rotated, or foreshortened view of an object. Naming was slower when the picture was presented 50 ms after the tone compared with 800 ms after the tone. Plane rotation effects were reduced (but not eliminated) at the short tone-picture stimulus onset asynchrony, but foreshortening effects were not reduced. The results implicate an early, prebottleneck locus for some processes compensating for plane rotation and a subsequent bottleneck or postbottleneck locus for compensation for foreshortening.

Adult↗
PubMed2000

Mitochondrial DNA phylogeography of the polytypic North American rat snake (Elaphe obsoleta): a critique of the subspecies concept.

Subspecies have been considered artificial subdivisions of species, pattern classes, or incipient species. However, with more data and modern phylogenetic techniques, some subspecies may be found to represent true species. Mitochondrial DNA analysis of the polytypic snake, Elaphe obsoleta, yields well-supported clades that do not conform to any of the currently accepted subspecies. Complete nucleotide sequences of the cytochrome b gene and the mitochondrial control region produced robust maximum-parsimony and maximum-likelihood trees that do not differ statistically. Both trees were significantly shorter than a most parsimonious tree in which each subspecies was constrained to be monophyletic. Thus, the subspecies of E. obsoleta do not represent distinct genetic lineages. Instead, the evidence points to three well-supported mitochondrial DNA clades confined to particular geographic areas in the eastern United States. This research underscores the potential problems of recognizing subspecies based on one or a few characters.

Animals↗
PubMed1999

Achieving visual object constancy across plane rotation and depth rotation.

Visual object constancy is the ability to recognise an object from its image despite variation in the image when the object is viewed from different angles. I describe research which probes the human visual system's ability to achieve object constancy across plane rotation and depth rotation. I focus on the ecologically important case of recognising familiar objects, although the recognition of novel objects is also discussed. Cognitive neuropsychological studies of patients with specific deficits in achieving object constancy are reviewed, in addition to studies which test neurally intact subjects. In certain cases, the recognition of invariant features allows objects to be recognised irrespective of the view depicted, particularly if small, distinctive sets of objects are presented repeatedly. In contrast, in most situations, recognition is sensitive to both the view in-plane and in-depth from which an object is depicted. This result suggests that multiple, view-specific, stored representations of familiar objects are accessed in everyday, entry-level visual recognition, or that transformations such as mental rotation or interpolation are used to transform between retinal images of objects and view-specific, stored representations.

Attention↗
PubMed1999

The effect of prior experience on recognition thresholds for plane-disoriented pictures of familiar objects.

We investigated plane rotation effects on the minimum presentation duration that is required in order to recognize pictures of familiar objects, using the method of ascending limits. Subjects made unspeeded verification responses, selecting from 126 written alternatives. Replicating similar identification studies in which brief, masked pictures (Lawson & Jolicoeur, 1998) were presented, disorientation reduced the efficiency of recognition. Mirroring the findings in speeded picture naming studies (e.g., Jolicoeur, 1985; Jolicoeur & Milliken, 1989), but in contrast to those of Lawson and Jolicoeur (1998), orientation effects were found over a wide range of views and were attenuated but not eliminated with experience with a given object. The results bridge the findings from unspeeded verification and speeded naming tasks. They suggest that the same orientation-sensitive processes are tapped in both cases, and that practice effects on these processes are object specific.

Adult↗
PubMed1998

The long-term impact of child abuse on religious behavior and spirituality in men.

OBJECTIVE: Two hypotheses were tested: (1) In a sample of adult men, past experience of child abuse (sexual, physical, or emotional) will be related to higher levels of reported alienation from religion and God as shown in lower rates of current religious behavior, higher frequency of spiritual "injury," and lower stability of religious behavior and experiences; (2) More "severe" forms of abuse will be associated with higher indicators of alienation. METHOD: Data were collected from 1,207 male veterans, 527 (43.7%) of whom reported being abused as a child. Each subject completed the Spiritual Issues Assessment, a large survey which includes data about: (1) KASL Religiosity Index; (2) The Spiritual Injury Scale; and (3) Religious items from the Westberg Personal Health Inventory. RESULTS: A history of sexual abuse was related to significantly greater spiritual injury and lower stability of spiritual behaviors and experiences, but not to overall rate of current religious behavior. Surprisingly, abuse was related to increased frequency of prayer and of "spiritual experience." Multivariate analyses indicate that the effect size is relatively small and the type of abuse was less important than the presence of any form of abuse. CONCLUSIONS: The findings suggest that the impact of childhood abuse is more complex than initially hypothesized. While abuse seems to be related to continuing spiritual injury and distress, it is also related to higher levels of some spiritual activities and experiences which are usually associated with positive spirituality.

Adult↗
PubMed1998

Salicylate toxicity masquerading as malignant hyperthermia.

We report a case of hyperpyrexia presumed due to topical salicylate toxicity occurring immediately following general anaesthesia for appendicectomy in an eleven year old boy. Some of the features strongly suggested the diagnosis of malignant hyperpyrexia.

Administration, Topical↗
PubMed1998

Adult dental visits in California: successes and challenges.

OBJECTIVES: This study sought to estimate and characterize the proportion of California adults who visited a dentist in the preceding year and to identify reasons for not going. METHODS: In 1995, 4,029 adults were interviewed by telephone as part of the California Behavioral Risk Factor Surveillance System. Items included recentness of a dental visit, dental insurance status, and number of teeth lost due to disease. Persons who had not seen a dentist within the preceding year were asked the main reason they had not gone. RESULTS: In 1995, 65.9% of adults reported visiting a dentist in the preceding twelve months. Use of dental services was greater among persons aged 35 years or older (70.4%) than among those aged 18-34 years (58.4%) and among those with dental insurance (74.9%) than those without (54.4%). Dental visits were less likely among adults living at or below 200 percent of the federal poverty level, those with less than a high school education, and the edentulous. Reasons most commonly cited for not seeing a dentist were no perceived reason to go (37.2%), cost (30.7%), and fear (9.2%). CONCLUSION: Substantial variation in use of dental services exists among California's adults. Achieving equity in access and opportunity for disease prevention in this state may require expanded dental insurance coverage and serious efforts in oral health promotion.

Adolescent↗
PubMed1998

Techniques and equipment for muscle mechanics.

The individual in vivo mechanical properties of muscle groups are not well known, and these data are important in simulations of a subject's movements, and analysis of measured movements. Discrepancies in the force-velocity relation between in vivo and in vitro measurements have been documented in previous investigations. A powerful, high precision dynamometer was designed and built to make in vivo tests on the elbow and ankle joints. Test data obtained with this machine did not exhibit the same discrepancies observed in previous experiments, which leads to the conclusion that the previous discrepancies resulted from the test method used.

Biomechanical Phenomena↗
PubMed1998

The effects of plane rotation on the recognition of brief masked pictures of familiar objects.

Two experiments examined the effects of plane rotation on the recognition of briefly displayed pictures of familiar objects, using a picture-word verification task. Mirroring the results of earlier picture naming studies (Jolicoeur, 1985; Jolicoeur & Milliken, 1989), plane rotation away from a canonical upright orientation reduced the efficiency of recognition, although in contrast to the results from picture naming studies, the rotation effects were not reduced with experience with the stimuli. However, the rotation effects were influenced by the visual similarity of the distractor objects to the picture of the object presented, with greater orientation sensitivity being observed when visually similar distractors were presented. We suggest that subjects use orientation-sensitive representations to recognize objects in both the present unspeeded verification and in the earlier speeded naming tests of picture identification.

Adult↗
PubMed1998

View-specific effects of depth rotation and foreshortening on the initial recognition and priming of familiar objects.

In a series of three experiments, we examined, first, the effects of viewpoint in depth on the efficiency of initial picture naming and, second, the effects of priming on subsequent naming. On initial presentation, foreshortened views were harder to name than were more typical (nonforeshortened) views. In addition, priming increased as a function of the similarity of the prime and target. Indeed, if a foreshortened view of an object had already been named, the subjects named a subsequent foreshortened view of that object as fast as or faster than they named a subsequent, more typical view. These results provide evidence against theories that predict full view-invariant object recognition and view-invariant priming of object recognition. Instead, the results support theories that suggest that object recognition is mediated by stored representations that are both view- and object-specific.

Adolescent↗
PubMed1996

View specificity in object processing: evidence from picture matching.

Four experiments investigated the types of representations mediating sequential visual matching of objects depicted at different depth rotations. Matching performance was affected by the similarity between depicted views of the objects. Effects of view similarity were not influenced by the presence of a meaningless mask in the interstimulus interval (ISI), but they were reduced by long ISIs and by familiarity with the stimuli. It is suggested that with longer ISIs or increased stimulus familiarity, a number of object representations are activated that, although abstracted from some image characteristics, remain view specific. Under these conditions, matching is less reliant on representations closely tied to the view of the initial stimulus presented. The results are consistent with both the derivation and the long-term representation of view-specific rather than view-invariant descriptions of objects.

Adolescent↗