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K Arbuthnott

Publications and source records attributed to K Arbuthnott.

7 recordsLinked to original sources
PubMed2000

Executive control in set switching: residual switch cost and task-set inhibition.

Executive processes necessary for flexibly switching between different tasks were studied using a set switching paradigm that requires participants to rapidly switch between different tasks across consecutive trials. Switch cost reflects poorer performance for task-switch trials than for consecutive same-task trials. Significant switch cost was observed even with considerable preparation time before a task-switch, an effect known as residual switch cost. This study tested the hypothesis that one process underlying residual switch cost is inhibition of the previous task-set. We used semantic categorization tasks to compare switch cost between alternating task series (ABA) and nonalternating series (ABC) in order to test the generality of a task-set inhibition effect previously observed with perceptual judgment tasks (Mayr & Keele, in press). The results yielded significant switch cost only for alternating tasks, in both response times and errors resulting from performance of the wrong task. Thus, resolving inhibition associated with previously abandoned task-sets may be the main process underlying residual switch costs, suggesting that task-set inhibition is an important executive control process.

Adolescent↗
PubMed2000

Trail making test, part B as a measure of executive control: validation using a set-switching paradigm.

Recent controversy surrounds the use of the Trail Making Test as a measure of cognitive flexibility, given that the Trail Making Test, Part B (TMT-B) also differs from Part A (TMT-A) in factors of motor control and perceptual complexity. The present study compared performance in the TMT and a set-switching task in order to test the assumption that cognitive flexibility is captured in TMT-B performance. Set-switching tasks have low motor and perceptual selection demands, and therefore provide a clearer index of executive function. In this study, participants made category judgments for digits, letters, or symbols across a series of trials, and performance for consecutive same-task trials was compared with task-switch trials. Results of the set-switching task indicated significant switch cost, but only for the situation of task alternation (e.g., an ABA series), suggesting that task-set inhibition may play a role in this effect. Alternating-switch cost was significantly correlated with TMT-B performance, especially with the TMT-B to TMT-A ratio (B/A). Cost for alternating switches was especially large for participants with B/A ratio > 3. These results provide direct evidence that the B/A ratio of performance in the TMT provides an index of executive function.

Adult↗
PubMed2000

Cognitive inhibition in selection and sequential retrieval.

Inhibitory models of working memory efficiency (Engle, 1996; Zacks & Hasher, 1994) assert that individual differences in working memory reflect the efficiency of inhibitory processes that exclude irrelevant information and suppress no-longer-relevant information. The present study examined the implication that these two inhibitory processes operate at consistent levels of efficiency within individuals by examining the correlation between two cognitive inhibition effects, negative priming and negative error priming. Negative priming involves slower response to a probe-trial target that was used as a to-be-ignored distractor on the immediately preceding prime trial. Negative error priming is the phenomenon that errors in a sequence of simple arithmetic trials are unlikely to involve the correct answer to the preceding problem. Participants received distractor-target pairs of simple addition problems and were required to produce the target problem sum. Negative priming was observed for prime distractors, whereas negative error priming was observed in connection with previous targets but not distractors. Consistent with the assumptions of these working memory models, the magnitudes of the two effects were significantly correlated.

Adolescent↗
PubMed1998

Improving the binding affinity of an antibody using molecular modeling and site-directed mutagenesis.

Activated Factor X releases F1.2, a 271-amino acid peptide, from the amino terminus of prothrombin during blood coagulation. A nine-amino acid peptide, C9 (DSDRAIEGR), corresponding to the carboxyl terminus of F1.2 was synthesized and used to produce a monoclonal antibody, TA1 (K(D)) 1.22 x 10(-6) M). To model the TA1 antibody, we entered the sequence information of the cloned TA1 Fv into the antibody modeling program, ABM, which combines homology methods, conformational search procedures, and energy screening and has proved to be a reliable and reproducible antibody modeling method. Using a novel protein fusion procedure, we expressed the C9 peptide fused to the carboxyl terminus of the PENI repressor protein from Bacillus licheniformis in Escherichia coli. We constructed fusion proteins containing alanine substitutions for each amino acid in the C9 epitope. Binding studies, using the C9 alanine mutants and TA1, and spatial constraints predicted by the modeled TA1 binding cleft enabled us to establish a plausible conformation for C9 complexed with TA1. Furthermore, based on binding results of conservative amino acid substitutions in C9 and mutations in the antibody, we were able to refine the complex model and identify antibody mutations that would improve binding affinity.

Alanine↗
PubMed1997

Relationship between isokinetic muscle strength and exercise capacity in chronic heart failure.

The exercise intolerance and excessive ventilatory response to exercise of chronic heart failure is associated with abnormalities of skeletal muscle function, in particular a reduction in muscle strength. Isometric and isokinetic leg muscle strength were measured in 10 patients with chronic heart failure and 10 age-matched controls. Each subject undertook maximal exercise testing to measure peak oxygen consumption (V(O2)) and the ventilatory response to exercise as measured by the slope of the relation between ventilation and carbon dioxide production (V(E)/V(CO2) slope). Quadriceps strength (mean (S.D.)) was reduced in heart failure as measured by isometric (444.9 (129.6) N vs. 556.0 (136.0); P<0.01) and isokinetic (123.6 (30.2) Nm vs. 146.8 (40.0); P=0.04). Hamstring strength was also reduced as measured by isokinetic testing (53.6 (15.6) Nm vs. 71.1 (28.1); P=0.02). Isokinetic and isometric strengths correlated, but not closely (r=0.52, P<0.001). There were negative correlations between the V(E)/V(CO2) slope, and isokinetic measures: with average torque, r=-0.62, P<0.004; with peak torque, r=-0.64, P=0.002. We have found evidence for reduced muscle function affecting both knee flexors and extensors. This reduction in muscle strength correlates with the ventilatory response to exercise. These observations lend support to the muscle hypothesis of the generation of symptoms in chronic heart failure.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Exercise dynamics at submaximal workloads in patients with chronic heart failure.

BACKGROUND: The aims of this study were to analyze the relationship between exercise at self-selected work loads and peak exercise performance in patients with chronic heart failure and to analyze possible relationships between gait pattern and exercise performance and ventilatory response to exercise in chronic heart failure. METHODS AND RESULTS: Twelve patients with stable chronic heart failure and 10 age- and build-matched control subjects undertook symptom-limited maximal exercise testing with metabolic gas exchange measurements to determine peak oxygen consumption (VO2) and the slope of the relationship between ventilation and carbon dioxide production (VE/VCO2 slope). Respiratory rate was also determined. Self-selected walking pace and cadence (steps per minute) were determined. Metabolic gas exchange analysis was repeated at matched low-level exercise and at self-selected walking pace. Self-selected exercise was at a lower speed for patients than control subjects (1.28 [0.22] vs 1.43 [0.19] m s-1), representing a similar proportion of peak oxygen consumption (63.6 [19.3]% vs 56.7 [25.4]%). There was a relationship between peak VO2 and VO2 at self-selected workload (r = .55, P < .001) and self-selected walking velocity (r = .58, P < .005). Gait analysis demonstrated that the reduction in self-selected velocity in heart failure patients was due to a reduced cadence (101.5 [8.7] steps/min vs 110.2 [9.1] steps/min, P < .01), not a reduction in stride length. There was a negative relationship between VE/VCO2 slope and self-selected cadence (r = -.68, P < .001) and a negative correlation between respiratory rate and cadence at self-selected workload (r = -.6, P < .005). CONCLUSIONS: Self-selected walking speed is at the same proportion of peak oxygen consumption in patients with heart failure as compared with control subjects, but a lower absolute level. Patients have the same stride length as normal control subjects. Ventilation is increased in patients, but there is no direct relationship between ventilation and gait.

Exercise Test↗