Thesis Chapters by Christopher L Hewitson
Word count (text): 17,942
Papers by Christopher L Hewitson
Journal of neurophysiology, 2023
People form metacognitive representations of their own abilities across a range of tasks. How the... more People form metacognitive representations of their own abilities across a range of tasks. How these representations are influenced by errors during learning is poorly understood. Here we ask how metacognitive confidence judgments of performance during motor learning are shaped by the learner's recent history of errors. Across four motor learning experiments, our computational modeling approach demonstrated that people's confidence judgments are best
Journal of Internal Medicine, 2007
Conclusions. HD is associated with significant reductions in F, tHcy and ADMA serum concentration... more Conclusions. HD is associated with significant reductions in F, tHcy and ADMA serum concentrations. The lack of significant effects of HD on endotheliumdependent vasodilatation could be secondary to the concomitant loss of factors either enhancing (F) or impairing (ADMA) endothelial function.
Comparative Cognition & Behavior Reviews, 2018
In this commentary, we highlight some relevant history of the situated cognition movement and the... more In this commentary, we highlight some relevant history of the situated cognition movement and then identify several issues with which we think further progress can be made. In particular, we address and clarify the relationship between situated cognition and antirepresentational approaches. We then highlight the heterogeneous nature of the concept of morphological computation by describing a less common way the term is used in robotics. Finally, we discuss some residual concerns about the mutual manipulability criterion and propose a potential solution.
Although human motor learning has been intensively studied for many decades, it remains unknown w... more Although human motor learning has been intensively studied for many decades, it remains unknown whether group differences are present in expert cohorts that must routinely cope with and learn new visuomotor mappings such as minimally invasive surgeons. Here we show that expert surgeons exhibit greater adaptation and generalization compared to naive controls in a standard visuomotor adaptation task. These findings run counter to a widespread background assumption in the field of motor learning that visuomotor adaptation performance should be largely uniform across the adult human population. Our findings also indicate that differences in basic visuomotor learning capacities, either innate or acquired, might be an important source of difficulty in learning and performing minimally invasive surgery. This information holds potential to guide surgical candidate selection or optimize training programs to address individual needs.
Hewitson CL, Whiting MJ, Barbara JA, Mangoni AA (Flinders University and Flinders Medical Centre,... more Hewitson CL, Whiting MJ, Barbara JA, Mangoni AA (Flinders University and Flinders Medical Centre, Adelaide, Australia). Acute effects of hae-modialysis on biochemical modulators of endothelial function. J Intern Med 2007; 262: 571-580. Objectives. To assess the acute effects of haemodialysis (HD) on biochemical factors modulating endothelial function. Setting. Academic medical centre. Subjects. Forty patients (age 63.5 ± 2.2 years, mean ± SEM) undergoing HD. Interventions. Folic acid (F), homocysteine (tHcy), asymmetric dimethylarginine (ADMA), high-sensitivity C-reactive protein (CRP) and malondialdehyde (MDA) were measured pre-HD, 1 h after commencing HD and within the last hour of HD (end-HD). Endo-thelium-dependent and-independent vasodilatation were measured by applanation tonometry (changes in augmentation index, AIx, postinhaled salbutamol and postsublingual nitroglycerin) in conjunction with biochemical measurements. Results. Marked reductions in serum F (616 ± 73 vs. 273 ± 30 nmol L)1 , P < 0.001), tHcy (16.3 ± 0.7 vs. 11.2 ± 0.5 lmol L)1 , P < 0.001) and ADMA (0.64 ± 0.02 vs. 0.47 ± 0.02 lmol L)1 , P < 0.001) occurred end-HD, whereas CRP and MDA levels did not significantly change. There was no significant change in endothelium-dependent vasodilatation, whereas endothelium-independent vasodilatation improved end-HD ()23.1 ± 1.9 vs.)17.3 ± 1.3%, P = 0.018). Regression analysis showed that both higher ADMA (P = 0.029) and lower F levels (P = 0.040) end-HD were determinants of reduced endothelium-dependent vasodilatation end-HD (R 2 = 0.23). Conclusions. HD is associated with significant reductions in F, tHcy and ADMA serum concentrations. The lack of significant effects of HD on endothelium-dependent vasodilatation could be secondary to the concomitant loss of factors either enhancing (F) or impairing (ADMA) endothelial function.
Visual Abstract Recent work suggests that the brain represents probability distributions and perf... more Visual Abstract Recent work suggests that the brain represents probability distributions and performs Bayesian integration during sensorimotor learning. However, our understanding of the neural representation of this learning remains limited. To begin to address this, we performed two experiments. In the first experiment, we replicated the key behavioral findings of Körding and Wolpert (2004), demonstrating that humans can perform in a Bayes-optimal manner by combining information about their own sensory uncertainty and a statistical distribution of lateral shifts encoun-Significance Statement Generalization provides unique insights into the motor learning process. However, this type of learning has typically been investigated using fixed or deterministic perturbations and noise-free feedback information, which are not naturalistic. Here, we replicate important findings indicating that information is integrated in a Bayes-optimal manner during sensorimotor learning under uncertainty. We then extend these findings by showing that this learning generalizes to the opposite limb. These results have implications for our understanding of the neural mechanisms of motor learning as well as practical application to the contexts of sport training and motor rehabilitation.
In this commentary, we highlight some relevant history of the situated cognition movement and the... more In this commentary, we highlight some relevant history of the situated cognition movement and then identify several issues with which we think further progress can be made. In particular, we address and clarify the relationship between situated cognition and antirepresentational approaches. We then highlight the heterogeneous nature of the concept of morphological computation by describing a less common way the term is used in robotics. Finally, we discuss some residual concerns about the mutual manipulability criterion and propose a potential solution. A Brief History of Situated Cognition Research We applaud Cheng's effort to bring concepts from the framework of situated cognition to a wider biological audience, including researchers working on insect behavior. It is also delightfully ironic. Cheng notes that although the idea of "situated cognition has been bantered in philosopher and cognitive science for some time now. .. its connection with nonhuman animals has a more recent history" (p. 11). Although he is correct to point out that recent philosophical discussions have focused on the human case, much of the early history had a different focus, closer to home for the target audience of this article. For deep theoretical reasons, many of the earliest discussions of embodied cognition among researchers in artificial intelligence (AI) and robotics centered on the rich, adaptive behavioral repertoires of simpler organisms including insects. Therefore, in many ways, the discussion of situated cognition has truly come full circle-from insects to humans and now back to insects again. Consider, for example, roboticist Rodney Brooks's (1991) seminal article "Intelligence Without Representation ," which perhaps more than any other single article served to launch the embodied cognition movement. A central goal of this article and much of Brooks's career was to build a research program in AI that drew inspiration from the intelligent behavior manifested by insects and other simpler biological organisms rather than humans. Brooks forcefully argued that researchers in AI had mistakenly assumed for too long that the hallmark of intelligence was disembodied reasoning or computation performed over explicit, language-like representations , instead of adaptive and flexible control of bodily action. According to Brooks, the latter is the real locus of natural (and so artificial) intelligence. This shift in
Methylated arginines and nitric oxide in end-stage renal disease: impact of inflammation, oxidative stress and haemodialysis
Biomarkers, 2013
To determine whether inflammation (C-reactive protein, CRP), oxidative stress (malondialdehyde, M... more To determine whether inflammation (C-reactive protein, CRP), oxidative stress (malondialdehyde, MDA) or haemodialysis (HD) affect associations between asymmetric (ADMA), symmetric (SDMA) dimethylarginine, NG-monomethyl-L-arginine (L-NMMA) and nitrite/nitrate (NOx) in end-stage renal disease (ESRD). Metabolites were measured pre-HD, after 1 hour and end-HD in 40 ESRD patients (age 63 ± 14 years). Positive associations between NOx and ADMA (p = 0.04), SDMA (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and L-NMMA (p = 0.04) were observed pre-HD. Associations weakened during HD but were not significantly influenced by CRP or MDA. HD, oxidative stress or inflammation did not significantly affect the positive associations between methylated arginines and NOx in ESRD.
Drafts by Christopher L Hewitson
Bioarchive, 2019
Although human motor learning has been intensively studied for many decades, it 20 remains unknow... more Although human motor learning has been intensively studied for many decades, it 20 remains unknown whether group differences are present in expert cohorts that must 21 routinely cope with and learn new visuomotor mappings such as minimally invasive 22 surgeons. Here we show that expert surgeons exhibit greater adaptation and 23 generalization compared to naive controls in a standard visuomotor adaptation task. 24 These findings run counter to a widespread background assumption in the field of motor 25 learning that visuomotor adaptation performance should be largely uniform across the 26 adult human population. Our findings also indicate that differences in basic visuomotor 27 learning capacities, either innate or acquired, might be an important source of difficulty in 28 learning and performing minimally invasive surgery. This information holds potential to 29 guide surgical candidate selection or optimize training programs to address individual 30 needs. 31 32 3 41 hospital stays [3]. Despite these advantages, the task environment in MIS places high 42 demands on surgeons, increasing the difficulty relative to open surgery for both initial 43 learning [4] and ongoing performance [3,5,6]. Since laparoscopic instruments are 44 controlled through small insertion points in the skin, instrument movements are often 45 mirror-reversed and counter-intuitive (e.g., leftward hand motion produces rightward 46 instrument tip motion, and vice versa). Because surgeons receive visual feedback 47
The aim of this work is to elucidate issues pertaining to the property of absolute acceleration.
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Thesis Chapters by Christopher L Hewitson
Papers by Christopher L Hewitson
Drafts by Christopher L Hewitson