Changing minds in a changing world

I defend a general rule for updating beliefs that takes into account both the impact of new evidence and changes in the subject??s location. The rule combines standard conditioning with a ??shifting?? operation that moves the center of each doxastic possibility forward to the next point where information arrives. I show that well-known arguments for conditioning lead to this combination when centered information is taken into account. I also discuss how my proposal relates to other recent proposals, what results it delivers for puzzles like the Sleeping Beauty problem, and whether there are diachronic constraints on rational belief at all.     

Minimal mimicry: Mere effector matching induces preference

Both mimicking and being mimicked induces preference for a target. The present experiments investigate the minimal sufficient conditions for this mimicry-preference link to occur. We argue that mere effector matching between one’s own and the other person’s movement is sufficient to induce preference, independent of which movement is actually performed. In Experiments 1 and 2, participants moved either their arms or legs, and watched avatars that moved either their arms or legs, respectively, without any instructions to mimic. The executed movements themselves and their pace were completely different between participants (fast circular movements) and targets (slow linear movements). Participants preferred avatars that moved the same body part as they did over avatars that moved a different body part. In Experiment 3, using human targets and differently paced movements, movement similarity was manipulated in addition to effector overlap (moving forward–backward or sideways with arms or legs, respectively). Only effector matching, but not movement matching, influenced preference ratings. These findings suggest that mere effector overlap is sufficient to trigger preference by mimicry.     

The ambivalence of challenge stressors: Time pressure associated with both negative and positive well-being

According to the challenge–hindrance model, challenge stressors contain both stressful and challenging aspects, hindrance stressors only stressful aspects. Typically, negative outcomes of challenge stressors refer to well-being (strain), positive outcomes to so-called work outcomes (e.g., productivity, intention to quit). As both effects occur simultaneously, the positive outcomes often emerge only when controlling for the negative effects. We suggest that the negative and the positive effects of challenge stressors may refer to well-being. Specifically, we propose challenge to indicate competence, thus fostering organization-based self-esteem (OBSE), which, in turn, should enhance more general indicators of positive well-being. We explored the effect of time pressure (a prototypical challenge stressor) on a general well-being variable (positive attitude towards life; PAL). We postulated challenge stressors to be associated with PAL positively via OBSE and negatively via strain. These processes should (a) result in a non-significant bivariate association, which should (b) become significant once strain is controlled (suppression), but (c) become insignificant again once OBSE is controlled (mediation). Using structural equation modeling, we could confirm our hypotheses in a cross-sectional study. Results confirm the inherently ambivalent nature of time pressure, containing both positive and negative variance. In line with our theoretical position, results suggest that the negative and the positive outcomes may be conceived in terms of different aspects of well-being, in addition to “work outcomes” that do not refer to well-being. This concept of challenge stressors may help to explain why many people do not reduce challenge stressors even when they could: Feeling good about themselves and their lives may, at least temporarily, outweigh the strain.     

Predicting others’ actions: evidence for a constant time delay in action simulation

Recent evidence indicates that humans can precisely predict the outcome of occluded actions. It has been suggested that these predictions arise from a mental simulation which might run in real-time. The present experiments aimed to specify the time course of this simulation process. Participants watched transiently occluded point-light actions and the temporal outcome after occlusion was manipulated. Participants were instructed to judge the temporal coherence of the action after a short (Experiment 1) and a long occlusion period (Experiment 2). Both experiments revealed a comparable negative point of subjective equality (PSE), indicating that action simulation took constantly longer than the observed action itself. Such a temporal error was not present when inverted actions were used, (Experiment 3) ruling out a pure visually driven effect. The results suggest that the temporal error is due to costs arising from a switch from action perception to an internal simulation process involving motor representations.     

Movement kinematics affect action prediction: comparing human to non-human point-light actions

The influence of movement kinematics on the accuracy of predicting the time course of another individual's actions was studied. A human point-light shape was animated with human movement (natural condition) and with artificial movement that was more uniform regarding velocity profiles and trajectories (artificial condition). During brief occlusions, the participants predicted the actions in order to judge after occlusion whether the actions were continued coherently in time or shifted to an earlier or later frame. Error rates and reaction times were increased in the artificial compared to the natural condition. The findings suggest a perceptual advantage for movement with a human velocity profile, corresponding to the notion of a close interaction between observed and executed movement. The results are discussed in the framework of the simulation account and alternative interpretations are provided on the basis of correlations between the velocity profiles of natural and artificial movements with prediction performance.     

Lasting effects of alcohol: Subliminal alcohol cues,impairment expectancies,and math performance

Many people believe that drinking alcohol reduces cognitive performance, and prior research has shown such expectancy‐related impairment even when people merely thought that the (non‐alcoholic) drink they consumed contained alcohol. This study tested whether subliminal priming with alcohol‐related cues would similarly result in expectancy‐consistent cognitive performance decrements. Additionally, the moderating role of alcohol use was examined. After assessing participants' baseline math performance, participants were primed with alcohol‐related or neutral words and then completed a post‐treatment math task. Whereas impairment expectancies had no influence on math performance in control participants, expectancies predicted math performance for participants primed with alcohol‐related words. As hypothesized, expectancy‐consistent impairment in performance was only observed among high alcohol users. The current findings suggest that, in the presence of alcohol‐related cues in the environment, some people may perform less on cognitive tasks even in the absence of actual or assumed alcohol consumption and without being aware of it. Copyright © 2011 John Wiley & Sons, Ltd.     

Diagnosing fatigue in gait patterns by support vector machines and self-organizing maps

The aim of the study was to train and test support vector machines (SVM) and self-organizing maps (SOM) to correctly classify gait patterns before, during and after complete leg exhaustion by isokinetic leg exercises. Ground reaction forces were derived for 18 gait cycles on 9 adult participants. Immediately before the trials 7–12, participants were required to completely exhaust their calves with the aid of additional weights (44.4 ± 8.8 kg). Data were analyzed using: (a) the time courses directly and (b) only the deviations from each individual’s calculated average gait pattern. On an inter-individual level the person recognition of the gait patterns was 100% realizable. Fatigue recognition was also highly probable at 98.1%. Additionally, applied SOMs allowed an alternative visualization of the development of fatigue in the gait patterns over the progressive fatiguing exercise regimen.     

Motor execution affects action prediction

Previous studies provided evidence of the claim that the prediction of occluded action involves real-time simulation. We report two experiments that aimed to study how real-time simulation is affected by simultaneous action execution under conditions of full, partial or no overlap between observed and executed actions. This overlap was analysed by comparing the body sides and the movement kinematics involved in the observed and the executed action. While performing actions, participants observed point-light (PL) actions that were interrupted by an occluder, followed by a test pose. The task was to judge whether the test pose depicted a continuation of the occluded action in the same depth angle. Using a paradigm proposed by Graf et al., we independently manipulated the duration of the occluder and the temporal advance of the test pose relative to occlusion onset (occluder time and pose time, respectively). This paradigm allows the assessment of real-time simulation, based on prediction performance across different occluder time/pose time combinations (i.e., improved task performance with decreasing time distance between occluder time and pose time is taken to reflect real-time simulation). The PL actor could be perceived as from the front or back, as indicated by task instructions. In Experiment 1 (front view instructions), evidence of action simulation was obtained for partial overlap (i.e., observed and performed action corresponded either in body side or movement kinematics), but not for full or no overlap conditions. The same pattern was obtained in Experiment 2 (back view instructions), ruling out a spatial compatibility explanation for the real-time pattern observed. Our results suggest that motor processes affect action prediction and real-time simulation. The strength of their impact varies as a function of the overlap between observed and executed actions.     

Estimation of the predictive power of the model in mixed‐effects meta‐regression: A simulation study

Several methods are available to estimate the total and residual amount of heterogeneity in meta‐analysis, leading to different alternatives when estimating the predictive power in mixed‐effects meta‐regression models using the formula proposed by Raudenbush (1994, 2009). In this paper, a simulation study was conducted to compare the performance of seven estimators of these parameters under various realistic scenarios in psychology and related fields. Our results suggest that the number of studies (k) exerts the most important influence on the accuracy of the results, and that precise estimates of the heterogeneity variances and the model predictive power can only be expected with at least 20 and 40 studies, respectively. Increases in the average within‐study sample size () also improved the results for all estimators. Some differences among the accuracy of the estimators were observed, especially under adverse (small k and ) conditions, while the results for the different methods tended to convergence for more optimal scenarios.