Action simulation in the human brain: Twelve questions

Although the idea of action simulation is nowadays popular in cognitive science, neuroscience and robotics, many aspects of the simulative processes remain unclear from empirical, computational, and neural perspectives. In the first part of the article, we provide a critical review and assessment of action simulation theories advanced so far in the wider literature of embodied and motor cognition. We focus our analysis on twelve key questions, and discuss them in the context of human and (occasionally) primate studies. In the second part of the article, we describe an integrative neuro-computational account of action simulation, which links the neural substrate (as revealed in neuroimaging studies of action simulation) to the components of a computational architecture that includes internal modeling, action monitoring and inhibition mechanisms.     

Newly observed microscopic planar defects on {111} in natural diamond

Abstract

Circular disc-crack-like defects randomly distributed on {111} planes have been discovered by 300kV transmission electron microscopy in diamond that had crystallized on non-faceted growth surfaces of mean orientation {100}. In a sample of ～ 100 defects, disc diameters were narrowly distributed about a mean of 1·2 μm and one in seven discs were located on a coplanar stacking fault of average diameter 2 μm. Discs totally enclosed within the specimen exhibit concentric moiré fringes covering their image areas when viewed obliquely, showing them to be dilated into thin lenticles. Internal pressures, deduced from moiré-fringe counts on six lenticles, were in the range 1·5 to 1·8 GPa.     

Reversible plasticity under nanoindentation of atomically flat and stepped surfaces of fcc metals

Using atomistic simulation, the indentation of single-crystalline Cu is investigated for both an ideal and a stepped (111) surface. Both systems exhibit an intermediate regime of reversible plasticity, characterized by the formation of extended stacking faults, which heal entirely upon withdrawal of the indenter. This regime can be employed to clarify the role of pure stacking fault generation and cross-slip in plasticity. Its existence reveals that, on the atomistic scale, plastic deformation is characterized by material transport rather than by the nucleation of stacking faults. Finally, we establish a criterion–based on the total displacement of particles–to determine after which indentation depth plasticity is generated irreversibly in the material.     

Thermodynamic consistency and fast dynamics in phase-field crystal modeling

A general formulation is presented to derive the equation of motion and demonstrate thermodynamic consistency for several classes of phase-field (PF) and PF crystal (PFC) models. It can be applied to models with a conserved and non-conserved phase-field variable, describing either locally uniform or periodic stable states, and containing slow as well as fast thermodynamic variables. The approach is based on an entropy functional formalism previously developed in the context of PF models for locally uniform states [P. Galenko and D. Jou, Phys. Rev. E 71 (2005) p.046125] and thus allows to extend several properties of the latter to PF models for periodic states, i.e., PFC models.     

Functional Anatomy of the Null Hypothesis and of Tests of It

The author compared simulations of the “true” null hypothesis (z) test, in which ò was known and fixed, with the t test, in which s, an estimate of ò, was calculated from the sample because the t test was used to emulate the “true” test. The true null hypothesis test bears exclusively on calculating the probability that a sample distance (mean) is larger than a specified value. The results showed that the value of t was sensitive to sampling fluctuations in both distance and standard error. Large values of t reflect small standard errors when n is small. The value of t achieves sensitivity primarily to distance only when the sample sizes are large. One cannot make a definitive statement about the probability or “significance” of a distance solely on the basis of the value of t.     

The effects of scenario-based risk information on perceptions of susceptibility to Chlamydia and HIV

Abstract

Objectives: The Self-Report Habit Index (SRHI) was originally reported as one-dimensional; however, habit has been described as characterised by several features. Moreover, one-dimensional models for the SRHI have demonstrated poor fit. Therefore, we aimed to compare multidimensional models with a one-dimensional model in both snacking and physical activity habits, besides examining further instrument characteristics.

Design: A cross-sectional study was conducted with high school and university students (n?=?555).

Main outcome measure: The SRHI adapted for physical activity and for snaking habits was applied at one time point.

Results: Nested models with one factor, two factors and three factors were compared. Next, a hierarchical second-order model was tested, and further validity issues, as well as invariance between habits, were examined. Three-dimensional models represented a better fit for both habits. However, fit was still inadequate in the snacking version. In addition, discriminant validity concerns emerged for the physical activity SRHI. Moreover, invariance between the snacking and the physical activity versions was not confirmed.

Conclusions: Considering the SRHI as composed by the dimensions of ‘lack of awareness’, ‘lack of control’ and ‘history of behavioural repetition’ seems to be more accurate. Nevertheless, our findings suggest that further research is needed.     

Measuring Situation Awareness in Virtual Environment-Based Training

We evaluated the efficacy of a computer-based situation awareness (SA) measurement system for training dismounted infantry SA in an urban terrain virtual reality (VR) simulation. Based on past research, we hypothesized that the SA measures would be sensitive to individual (squad leader) differences, and that the frequency of specific probes would reveal differences in critical SA requirements among scenarios. Three infantry squads performed multiple trials across two different scenarios. A confederate platoon leader posed probes to squad leaders during trials and experts made ratings afterward. Results revealed squad leaders had similar responses to probes, despite differences in combat experience. Analysis of probe frequency revealed different high priority SA elements and decisions for each scenario. The SA behavior and communication ratings revealed differences among squads, which trended with experience. Measures of SA were also consistent across the test scenario as a result of similar mission types and task difficulties. We discuss the implication of our findings for future research and theory within this area.     

PC-Based Game Features That Influence Instruction and Learner Motivation

PC-based games are currently being used for military training, but the instructional and motivational features of such technology are not well understood. To identify features of training games that influence instruction and motivation, a popular first-person-perspective game with a military theme was analyzed empirically. Twenty-one participants played the “basic training” portion of the game, which included Army background information, virtual marksmanship training, an obstacle course, virtual weapons familiarization, and an urban terrain training mission. The results of this research provide useful information to individuals developing training games, desktop simulations, and interactive multimedia courseware to meet optimal training objectives and strategies.     

Obtaining the best value for money in adaptive sequential estimation

In [Kujala, J. V., Richardson, U., &; Lyytinen, H. (2010). A Bayesian-optimal principle for learner-friendly adaptation in learning games. Journal of Mathematical Psychology, 54(2), 247–255], we considered an extension of the conventional Bayesian adaptive estimation framework to situations where each observable variable is associated with a certain random cost of observation. We proposed an algorithm that chooses each placement by maximizing the expected gain in utility divided by the expected cost. In this paper, we formally justify this placement rule as an asymptotically optimal solution to the problem of maximizing the expected utility of an experiment that terminates when the total cost overruns a given budget. For example, the cost could be defined as the random time taken by each trial in an experiment, and one might wish to maximize the expected total information gain over as many trials as can be completed in 15 min. A simple, analytically tractable example is considered.