Estimating the Relevance of World Disturbances to Explain Savings, Interference and Long-Term Motor Adaptation Effects

Recent studies suggest that motor adaptation is the result of multiple, perhaps linear processes each with distinct time scales. While these models are consistent with some motor phenomena, they can neither explain the relatively fast re-adaptation after a long washout period, nor savings on a subsequent day. Here we examined if these effects can be explained if we assume that the CNS stores and retrieves movement parameters based on their possible relevance. We formalize this idea with a model that infers not only the sources of potential motor errors, but also their relevance to the current motor circumstances. In our model adaptation is the process of re-estimating parameters that represent the body and the world. The likelihood of a world parameter being relevant is then based on the mismatch between an observed movement and that predicted when not compensating for the estimated world disturbance. As such, adapting to large motor errors in a laboratory setting should alert subjects that disturbances are being imposed on them, even after motor performance has returned to baseline. Estimates of this external disturbance should be relevant both now and in future laboratory settings. Estimated properties of our bodies on the other hand should always be relevant. Our model demonstrates savings, interference, spontaneous rebound and differences between adaptation to sudden and gradual disturbances. We suggest that many issues concerning savings and interference can be understood when adaptation is conditioned on the relevance of parameters

Predicting the Effect of Surface Texture on the Qualitative Form of Prehension

Reach-to-grasp movements change quantitatively in a lawful (i.e. predictable) manner with changes in object properties. We explored whether altering object texture would produce qualitative changes in the form of the precontact movement patterns. Twelve participants reached to lift objects from a tabletop. Nine objects were produced, each with one of three grip surface textures (high-friction, medium-friction and low-friction) and one of three widths (50 mm, 70 mm and 90 mm). Each object was placed at three distances (100 mm, 300 mm and 500 mm), representing a total of 27 trial conditions. We observed two distinct movement patterns across all trials—participants either: (i) brought their arm to a stop, secured the object and lifted it from the tabletop; or (ii) grasped the object ‘on-the-fly’, so it was secured in the hand while the arm was moving. A majority of grasps were on-the-fly when the texture was high-friction and none when the object was low-friction, with medium-friction producing an intermediate proportion. Previous research has shown that the probability of on-the-fly behaviour is a function of grasp surface accuracy constraints. A finger friction rig was used to calculate the coefficients of friction for the objects and these calculations showed that the area available for a stable grasp (the ‘functional grasp surface size’) increased with surface friction coefficient. Thus, knowledge of functional grasp surface size is required to predict the probability of observing a given qualitative form of grasping in human prehensile behaviour

Comparison between REBT and Visual/Kinaesthetic Dissociation in the Treatment of Panic Disorder: An Empirical Study

The aim of this study was to test the efficacy of two brief treatment methods for panic disorder: Rational Emotive Behaviour Therapy (REBT) and Visual/Kinaesthetic Dissociation (VKD), neither of which have been the object of scientific enquiry. The study is a two-way between-groups pre-test/post-test experimental design with baseline and follow-up measures. An innovative four-session treatment protocol was developed for each treatment method. Eighteen participants in North-East Surrey, England, who responded to media advertisements for cognitive-behavioural treatment for panic disorder and who met Diagnostic and Statistical Manual of Mental Disorders criteria for panic disorder with or without agoraphobia were randomly assigned to either REBT or VKD. Pre-test/post-test changes in panic were measured using the ACQ, PASQ, and HADS scales and a global panic rating measure. At post-test there was a statistically significant improvement on all measures for both groups, which was maintained at one-month follow-up. Taking into consideration limitations such as the small sample size and a short follow-up period, implications of this study and recommendations for future research are discussed

Lingering delays in a go/no-go task: mind wandering delays thought probes reliably but not reaction times

BACKGROUND: In a go/no-go task, changes to the inter-trial interval (ITI) or the press percentage (PP) are known to have decelerating effects on both reaction time and on thought probe response time. The mental causes of these delays remain obscure. AIMS: To see whether the delaying effects of ITI and PP are additive, and to determine whether these timing effects are linked with mental states detectable by subjective ratings. METHODS: An 18-minute online experiment with 60 participants who each performed 8 versions of the ToVA with different ITIs and PPs. At the end of each block were mind wandering (MW) thought probes and rating scales for subjective effort and awareness. RESULTS: The decelerating effects of long ITIs, low PPs, and MW seem to be synergistic, but the effects of individual factors on thought probes seem brittle. A version of the ToVA with zero no-go-stimuli spontaneously and implicitly accelerated mean reaction time significantly. That version also quickened three subsequent response times for rating tasks by hundreds of milliseconds, which suggests that the basis of this effect is a lingering mental state (or substrate). None of the subjective ratings measured were strongly related to the reaction time delay, although MW seems to delay the thought probe response. CONCLUSION: The strategic effect on both the reaction time and the thought probe response time is presumably a change in the speed-accuracy trade-off in which the participant adopts a mental strategy that speeds up thinking by reducing caution, so caution needs to be subjectively measured

Intentional mind wandering is objectively linked to low effort and tasks with high predictability

BACKGROUND: Intentional Mind Wandering (IMW) is proposed to be a low executive control state in response to boredom, to distinguish it from unintentional mind wandering (UMW), which may be a low arousal state in response to exhaustion of resources. AIMS: To demonstrate that the objective differences between IMW and UMW reflect the subjective difference that IMW is linked to a low effort and high predictability strategy. METHODS: The metronome response task (MRT) requires participants to predict when the next tone in a regular series will occur. Inter-Trial Interval (ITI) variants of the MRT were presented in blocks of ∼ 90 seconds. RESULTS: The most predictable version of MRT resulted in the percentage of reported IMW doubling, whereas UMW remained similar in all three versions of the MRT. IMW necessitates subjective effort to be low (capped at 5 on a 1-9 scale). IMW in easy and predictable versions of the task resulted in normal performance, whereas IMW during difficult tasks that required sustained attention led to poor performance and occasional errors. IMW during the least predictable MRT led to a significantly higher rate of omission errors (compared to on-task or UMW), and also to a higher maximum-in-block reaction time, as predicted by the worst performance rule. Conscientiousness was linked to reduced IMW (but not reduced UMW), higher on-task probes, increased effort, and improved prediction accuracy. CONCLUSIONS: Subjective assessment of task difficulty predisposes IMW, with transient increases of both omission errors and slow lapses due to diminished allocation of cognitive resources

Age at Menarche and Time Spent in Education: A Mendelian Randomization Study.

Menarche signifies the primary event in female puberty and is associated with changes in self-identity. It is not clear whether earlier puberty causes girls to spend less time in education. Observational studies on this topic are likely to be affected by confounding environmental factors. The Mendelian randomization (MR) approach addresses these issues by using genetic variants (such as single nucleotide polymorphisms, SNPs) as proxies for the risk factor of interest. We use this technique to explore whether there is a causal effect of age at menarche on time spent in education. Instruments and SNP-age at menarche estimates are identified from a Genome Wide Association Study (GWAS) meta-analysis of 182,416 women of European descent. The effects of instruments on time spent in education are estimated using a GWAS meta-analysis of 118,443 women performed by the Social Science Genetic Association Consortium (SSGAC). In our main analysis, we demonstrate a small but statistically significant causal effect of age at menarche on time spent in education: a 1 year increase in age at menarche is associated with 0.14 years (53 days) increase in time spent in education (95% CI 0.10-0.21 years, p = 3.5 × 10-8). The causal effect is confirmed in sensitivity analyses. In identifying this positive causal effect of age at menarche on time spent in education, we offer further insight into the social effects of puberty in girls