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Biomedical subjects

W Arthur

Publications and source records attributed to W Arthur.

At least 19 recordsLinked to original sources
PubMed2002

The interaction between developmental bias and natural selection: from centipede segments to a general hypothesis.

Do limitations to the ways in which mutations can alter developmental processes help to determine the direction of phenotypic evolution? In the early days of neo-Darwinism, the answer given to this question was an emphatic 'no'. However, recent work, both theoretical and empirical, argues that the answer should at least be 'sometimes', and possibly even a straightforward 'yes'. Here, I examine the key concept of developmental bias, which encompasses both developmental constraint and developmental drive. I review the case of centipede segment number, which is a particularly clear example of developmental bias, but also a rather unusual one. I then consider how, in general terms, developmental bias and natural selection might interact, with the result that it is their interaction, rather than either process on its own, that determines evolutionary direction. Essentially, the whole argument is about the extent to which phenotypic variation is developmentally structured as opposed to amorphous or random. This issue can be traced back to the very beginning of evolutionary biology, and in particular to a difference of opinion between Darwin and Wallace, who emphasized, respectively, character correlation and character independence.

Animals↗
PubMed2001

Knowledge structures and the acquisition of a complex skill.

The purpose of this study was to examine the viability of knowledge structures as an operationalization of learning in the context of a task that required a high degree of skill. Over the course of 3 days, 86 men participated in 9 training sessions and learned a complex video game. At the end of acquisition, participants' knowledge structures were assessed. After a 4-day nonpractice interval, trainees completed tests of skill retention and skill transfer. Findings indicated that the similarity of trainees' knowledge structures to an expert structure was correlated with skill acquisition and was predictive of skill retention and skill transfer. However, the magnitude of these effects was dependent on the method used to derive the expert referent structure. Moreover, knowledge structures mediated the relationship between general cognitive ability and skill-based performance.

Adolescent↗
PubMed2001

Clinical use of intracardiac impedance: current applications and future perspectives.

For over 40 years the measurement of intracardiac impedance has been proposed as a method of assessing the contractile state of the heart muscle. This technique requires the positioning of one or more intracavitary electrodes and the generation of an electric field from an alternating current source. Variations in the calculated impedance signal reflect changes in the ventricular blood pool volume adjacent to the electrodes. Intracardiac impedance measurement has been successfully developed as a research tool to assess myocardial contractility, and from this, clinical uses have evolved. Commercial rate responsive pacing systems use intracardiac impedance to assess the inotropic state of the heart. Further development of this technology might allow hemodynamic discrimination of cardiac arrhythmias.

Animals↗
PubMed2001

Hyperkalemia diagnosed by implantable cardioverter defibrillator T wave sensing.

A patient with congestive heart failure and an ICD had undergone atrioventricular nodal ablation and optimization of heart failure medical therapy. Intracardiac T wave sensing by the ICD drew attention to the new development of asymptomatic hyperkalemia. Surface ECG features of hyperkalemia were not readily identified due to pacemaker dependence.

Defibrillators, Implantable↗
PubMed2001

Motor vehicle crash involvement and moving violations: convergence of self-report and archival data.

In the crash involvement literature, it is generally assumed that archival and other "objective" criterion data are superior to self-reports of crash involvement. Using 394 participants (mean age = 36.23 years), the present study assessed the convergence of archival and self-report measures of motor vehicle crash involvement and moving violations. We also sought to determine whether predictor/criterion relationships would vary as a function of criterion type (i.e., archival vs. self-report), and if a combination of both criteria would result in better prediction than would either by itself. The degree of agreement between the two criterion sources was low, with participants self-reporting more crashes and tickets than were found in their state records. Different predictor/criterion relationships were also found for the two criterion types; stronger effects were obtained for self-report data. Combining the two criteria did not result in relationships stronger than those obtained for self-reports alone. Our findings suggest that self-report data are not inherently inferior to archival data and, furthermore, that the two sources of data cannot be used interchangeably. Actual or potential applications include choosing the appropriate criterion to use, which, as the finding of this study reveals, may depend on the purpose of the investigation.

Accidents, Traffic↗
PubMed2000

Latitudinal cline in segment number in an arthropod species, Strigamia maritima.

Arthropods vary more than 30-fold in segment number. The evolutionary origins of differences in segment number among species must ultimately lie in intraspecific variation. Yet paradoxically, in most groups of arthropods, the number of segments is fixed for each species and shows no intra- or interpopulation variation at all. Geophilomorph centipedes are an exception to this general rule, and exhibit intraspecific variation in segment number, with differences between individuals being determined during embryonic development and hence independent of population age structure. Significant differences in segment number between different geographical populations of the same species have been previously reported, but insufficient sampling has been conducted to reveal any particular geographical pattern. Here, we reveal a latitudinal cline in segment number in the geophilomorph species Strigamia maritima: segment number in British populations decreases with distance north. This is the first such cline to be reported for any centipede species; indeed as far as we are aware it is the first such cline reported for any arthropod species. In vertebrates, fish are known to exhibit a latitudinal cline in segment number, but interestingly, this is in the opposite direction; fish add segments with increasing latitude, centipedes subtract them.

Animals↗
PubMed2000

The measurement of impedance to assess myocardial contractility and rhythm stability.

By introducing an alternating current through the ventricular cavity via a multipolar catheter the potential difference measured between adjacent electrodes can be used to assess ventricular volume. This is possible by the measurement of intracardiac impedance. The data obtained can be used to construct pressure-volume loops allowing the continuous real-time assessment of myocardial contractility. Clinical applications of this research tool are now becoming apparent. Further derivations of impedance measurement have been incorporated into commercially available permanent pacing systems, allowing effective heart rate modulation.

Electric Impedance↗
PubMed2000

A dyadic protocol for training complex skills: a replication using female participants.

The effectiveness and efficiency of the active interlocked modeling (AIM) dyadic protocol in training complex skills has been extensively demonstrated. However, past evaluation studies have all used male participants exclusively. Consequently, the present study investigated the generalizability of the effectiveness and efficiency gains to women. We randomly assigned 108 female participants to either the AIM-dyad condition or a standard individual control training condition. The results supported the robustness and viability of the AIM protocol. Although their overall performance was lower than that obtained for men in previous studies, women trained in the AIM-dyad condition performed as well as those trained in the individual condition. Thus, the efficiency gains associated with the AIM-dyad protocol, which result from the ability to train two people simultaneously to reach the same performance level as a single person with no increase in training time or machine cost, are generalizable to female participants. The applied and basic research implications of the present study are discussed within the context of well-documented male/female differences in the performance of complex psychomotor tasks. For instance, given the number of women entering the workforce and the significant proportion of women in professions previously deemed to be male-dominated (e.g., air navigation), it is reassuring to know that sex differences in task performance do not necessarily imply sex differences in the effectiveness of training protocols.

Adult↗
PubMed1999

The pattern of variation in centipede segment number as an example of developmental constraint in evolution

The range of animal morphologies observed in nature is partly determined by natural selection. However, there is no agreement yet regarding whether it is also partly determined by developmental constraint. Testing for the effects of constraint has been difficult due to the lack of both an appropriate null model and a sufficiently simple system capable of yielding unambiguous results regarding the model's plausibility. Here we examine the case of variation in segment number in geophilomorph centipedes. Curiously, while this ranges between 29 and 191, there are no species in which an even number of segments is observed, in contrast to about 1000 species with odd numbers of segments. It seems unlikely that this distribution of character values is determined by selection alone. Using an approach based on Bayesian inference, we attempt to quantify the probability of obtaining the observed distribution of values given a null model in which developmental constraint is absent. Since this probability is in the region of 10(-20), we conclude that constraint must be involved. We discuss various implications of this conclusion, and comment on the unexpected absence of neoteny and progenesis in centipede evolution. Copyright 1999 Academic Press.

Journal Article↗
PubMed1997

Effects of colliery waste on littoral communities in north-east England.

Colliery waste input has a detrimental effect on the species richness and alpha diversity of sandy and rocky shore communities in north-east England. On sandy shores at the shore levels Chart Datum (CD) + 1.2 to 1.5 m (low shore) and CD + 2.7 to 3.0 m (mid-shore), a maximum of two species of macroinvertebrates per shore level was found at sites heavily contaminated by colliery waste input. In contrast, typically about eight species were found at uncontaminated shores. At the shore level CD + 4.2 to 4.5 m (high shore), the species richness and diversity of fauna were not detectably affected by colliery waste input. On rocky shores that were uncontaminated, 12-15 species of macroalgae were found, whereas only five to eight species were found at contaminated shores. The absentees were usually ephemeral, early successional species. Macroalgal biomass, although less at contaminated shores, showed no significant relationship with colliery waste input. However, the alpha diversity of animal communities on rocky shores was, on occasions, significantly increased where colliery waste inputs occurred. The physical properties of colliery waste are likely to be the reason for the effects observed on both sandy and rocky shores, since many of the leachable chemicals in colliery waste are leached during the period that it spends on the sea bed before accumulating in the intertidal zone.

Journal Article↗
PubMed1996

The five-factor model, conscientiousness, and driving accident involvement.

Personality researchers and theorists are approaching consensus on the basic structure and constructs of personality. Despite the apparent consensus on the emergent five-factor model (Goldberg, 1992, 1993), less is known about external correlates of separate factors. This research examined the relations between Conscientiousness, one dimension of the model, and driving accident involvement. Using multiple measures in independent samples drawn from college students (N = 227) and a temporary employment agency (N = 250), the results generally demonstrate a significant inverse relation between Conscientiousness and driving accident involvement; individuals who rate themselves as more self-disciplined, responsible, reliable, and dependable are less likely to be involved in driving accidents than those who rate themselves lower on these attributes. The findings are consistent with other research demonstrating the relations among Conscientiousness and other tasks and job performance. Suggestions for future research are discussed.

Accidents, Traffic↗
PubMed1996

Effectiveness of individual and dyadic training protocols: the influence of trainee interaction anxiety.

The present study focuses on the consequences of the social dynamics that are created whenever two or more individuals are brought together for the purpose of training. An investigation of the role of individual differences in interaction anxiety on training outcomes demonstrated that the comparative effectiveness of dyadic versus individual protocols for computer-based training is moderate by trainees' level of interaction anxiety. Specifically, assignment to a dyadic protocol adversely affected the performance of high-interaction-anxiety participants but appeared to be advantageous for low-interaction-anxiety participants. Implications are discussed for changing the design and implementation of computer-based protocols for training groups and individuals in military and industrial training centers.

Adult↗