Posture and motion variability in non-repetitive manual materials handling tasks

In developing a motion prediction model it is important to initially consider the sources of variability that a model should reproduce. This initial step is followed by model evaluation, where the variability predicted by the model can be a useful test parameter. An existing lifting-motion dataset collected under controlled laboratory conditions was employed here to evaluate quantitatively some important sources of variability for lift motion modeling. The main source of variability was the segment being analyzed, which accounted for more than 20% of the overall variability. There was substantial left-right symmetry in individual segment variability estimates, which were largest for the upper arm segment and tended to be larger for the upper limbs than the lower limbs. Task-related factors accounted for variability mainly as a function of the segment being considered. Within-participant variability contributions to the dataset were relatively small, whereas the contribution of between-participants variability was dependent on the segment (as large as 50%) and could indicate different lifting strategies across participants. Variability was found to remain relatively constant across the different stages of the lifting movements. Implications of these results for the development and evaluation of motion prediction models are presented. Specifically, while task characteristics may be important modifiers of the mean segment trajectory during a lifting movement, their influence on variability differs based on the segment that is being considered. The relevance of the findings is discussed in terms of their utility in the ergonomic design of tasks and work spaces.     

New measure o f perceived motorcompetence for children ages 4 to 6 years

The purpose of this study was to develop and validate a test for the assessment of perceived motor competence in young children ages 4 to 6 years old. The structure of the Children's Perception of Motor Competence Scale was analyzed through exploratory and confirmatory factor analysis with 495 children between 4 and 6 years of age. A second-order model was selected and consisted of one scale of Perceived General Motor Competence and two subscales, Perceived Gross Motor Competence and Perceived Fine Motor Competence. The number of items was 22. This test showed acceptable internal reliability: global scale (alpha = .81), Perceived Gross Motor Competence (alpha = .80), and Perceived Fine Motor Competence (alpha = .65). Children manifested accuracy in the assessment of the competence. Perceived motor competence was related to actual motor competence as measured by the Movement ABC Test and by an observational scale used by Physical Education teachers. There were no sex differences. The Children's Perception of Motor Competence Scale could be considered an interesting assessment test for identifying current self-perceptions of motor competence in young children.     

Cholinergic septo-hippocampal innervation is required for trace eyeblink classical conditioning

We studied the effects of a selective lesion in rats, with 192-IgG-saporin, of the cholinergic neurons located in the medial septum/diagonal band (MSDB) complex on the acquisition of classical and instrumental conditioning paradigms. The MSDB lesion induced a marked deficit in the acquisition, but not in the retrieval, of eyeblink classical conditioning using a trace paradigm. Such a deficit was task-selective, as lesioned rats were able to acquire a fixed-interval operant conditioning as controls, and was not due to nonspecific motor alterations, because spontaneous locomotion and blink reflexes were not disturbed by the MSDB lesion. The deficit in the acquisition of a trace eyeblink classical conditioning was reverted by the systemic administration of carbachol, a nonselective cholinergic muscarinic agonist, but not by lobeline, a nicotinic agonist. These results suggest a key role of muscarinic denervation on the acquisition of new motor abilities using trace classical conditioning procedures. It might also be suggested that muscarinic agents would be useful for the amelioration of some associative learning deficits observed at early stages in patients with Alzheimer's disease.     

Sampling plans for fitting the psychometric function

Research on estimation of a psychometric function psi has usually focused on comparing alternative algorithms to apply to the data, rarely addressing how best to gather the data themselves (i.e., what sampling plan best deploys the affordable number of trials). Simulation methods were used here to assess the performance of several sampling plans in yes-no and forced-choice tasks, including the QUEST method and several variants of up-down staircases and of the method of constant stimuli (MOCS). We also assessed the efficacy of four parameter estimation methods. Performance comparisons were based on analyses of usability (i.e., the percentage of times that a plan yields usable data for the estimation of all the parameters of psi) and of the resultant distributions of parameter estimates. Maximum likelihood turned out to be the best parameter estimation method. As for sampling plans, QUEST never exceeded 80% usability even when 1000 trials were administered and rendered accurate estimates of threshold but misestimated the remaining parameters. MOCS and up-down staircases yielded similar and acceptable usability (above 95% with 400-500 trials) and, although neither type of plan allowed estimating all parameters with optimal precision, each type appeared well suited to estimating a distinct subset of parameters. An analysis of the causes of this differential suitability allowed designing alternative sampling plans (all based on up-down staircases) for yes-no and forced-choice tasks. These alternative plans rendered near optimal distributions of estimates for all parameters. The results just described apply when the fitted psi has the same mathematical form as the actual psi generating the data; in case of form mismatch, all parameters except threshold were generally misestimated but the relative performance of all the sampling plans remained identical. Detailed practical recommendations are given.     

Are Wittgenstein’s Hinges Rational World-Pictures? The Groundlessness Theory Reconsidered

Some philosophers have argued that Wittgenstein’s hinges, the centrepiece of his book On Certainty, are the “ungrounded ground” on which knowledge rests. It is usually understood by this that hinges provide a foundation for knowledge without being themselves epistemically warranted. In fact, Wittgenstein articulates that hinges lack any truth-value and are neither justified nor unjustified. This inevitably places them wholly outside the categorial framework of JTB epistemology. What I call the “groundlessness interpretation”, inspired by OC 166, understands the fundamental pieces of our cognitive scaffolding this way. The view has been largely successful. I argue that this interpretation is incomplete for two basic reasons: first, it is not based on undisputed evidence; second, by assuming that hinges are committed to reality by epistemic fiat, it looks as if Wittgenstein is asking us to blindly trust them regardless of their actual content. Contrary to this, I argue that Wittgenstein describes hinges as illuminating world-pictures that reflect reality and are answerable to facts in a derivate way. As the book shows, hinges originate in our engagement with reality and, while considered unquestionable, could be challenged, reassessed, and replaced by new ones. This indicates that hinges are both the result of knowledge-acquisition and somewhat continuous with one’s set of beliefs. It follows that hinges are ultimately rational, and so, apt instruments to confront scepticism.

     

Personality and creativity

Previous research has provided conflicting accounts of the effects of personality on creative behaviour. This study examines the issue by means of factor analysis and multivariate analysis of variance. Different measures of creative behaviour and cognitive abilities are correlated with personal characteristics such as psychoticism, extraversion and other measures of personality. The results are consistent with the idea that different forms of creative behaviour are related to distinct characteristics of personality.