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.     

Gaze behaviour during space perception and spatial decision making

A series of four experiments investigating gaze behavior and decision making in the context of wayfinding is reported. Participants were presented with screenshots of choice points taken in large virtual environments. Each screenshot depicted alternative path options. In Experiment 1, participants had to decide between them to find an object hidden in the environment. In Experiment 2, participants were first informed about which path option to take as if following a guided route. Subsequently, they were presented with the same images in random order and had to indicate which path option they chose during initial exposure. In Experiment 1, we demonstrate (1) that participants have a tendency to choose the path option that featured the longer line of sight, and (2) a robust gaze bias towards the eventually chosen path option. In Experiment 2, systematic differences in gaze behavior towards the alternative path options between encoding and decoding were observed. Based on data from Experiments 1 and 2 and two control experiments ensuring that fixation patterns were specific to the spatial tasks, we develop a tentative model of gaze behavior during wayfinding decision making suggesting that particular attention was paid to image areas depicting changes in the local geometry of the environments such as corners, openings, and occlusions. Together, the results suggest that gaze during a wayfinding tasks is directed toward, and can be predicted by, a subset of environmental features and that gaze bias effects are a general phenomenon of visual decision making.     

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.     

The development of causal categorization

Two experiments examined the impact of causal relations between features on categorization in 5- to 6-year-old children and adults. Participants learned artificial categories containing instances with causally related features and noncausal features. They then selected the most likely category member from a series of novel test pairs. Classification patterns and logistic regression were used to diagnose the presence of independent effects of causal coherence, causal status, and relational centrality. Adult classification was driven primarily by coherence when causal links were deterministic (Experiment 1) but showed additional influences of causal status when links were probabilistic (Experiment 2). Children's classification was based primarily on causal coherence in both cases. There was no effect of relational centrality in either age group. These results suggest that the generative model (Rehder, 2003a) provides a good account of causal categorization in children as well as adults.     

Children's representation of symbolic and nonsymbolic magnitude examined with the priming paradigm

How people process and represent magnitude has often been studied using number comparison tasks. From the results of these tasks, a comparison distance effect (CDE) is generated, showing that it is easier to discriminate two numbers that are numerically further apart (e.g., 2 and 8) compared with numerically closer numbers (e.g., 6 and 8). However, it has been suggested that the CDE reflects decisional processes rather than magnitude representation. In this study, therefore, we investigated the development of symbolic and nonsymbolic number processes in kindergartners and first, second, and sixth graders using the priming paradigm. This task has been shown to measure magnitude and not decisional processes. Our findings revealed that a priming distance effect (PDE) is already present in kindergartners and that it remains stable across development. This suggests that formal schooling does not affect magnitude representation. No differences were found between the symbolic and nonsymbolic PDE, indicating that both notations are processed with comparable precision. Finally, a poorer performance on a standardized mathematics test seemed to be associated with a smaller PDE for both notations, possibly suggesting that children with lower mathematics scores have a less precise coding of magnitude. This supports the defective number module hypothesis, which assumes an impairment of number sense.     

Constraints on arm selection processes when reaching: degrees of freedom and joint amplitudes interact to influence limb selection

With an interest in identifying the variables that constrain arm choice when reaching, the authors had 11 right-handed participants perform free-choice and assigned-limb reaches at 9 object positions. The right arm was freely selected 100% of the time when reaching to positions at 30° and 40° into right hemispace. However, the left arm was freely selected to reach to positions at -30° and -40° in left hemispace 85% of the time. A comparison between free- and assigned-limb reaching kinematics revealed that free limb selection when reaching to the farthest positions was constrained by joint amplitude requirements and the time devoted to limb deceleration. Differences between free- and assigned-arm reaches were not evident when reaching to the midline and positions of ±10°, even though the right arm was freely selected most often for these positions. Different factors contribute to limb selection as a function of distance into a specific hemispace.     

Modulation of afterhyperpolarization evoked by doublets and increasing number of stimuli in rat motoneurons

The authors studied the influence of variable stimulation patterns on parameters of afterhyperpolarization (AHP) in rat spinal motoneurons using intracellular recording of antidromic action potentials. The action potentials analyzed were evoked by either (a) a single stimulus or pair of stimuli with gradually increasing interpulse intervals (IPI) of 5-20 ms or (b) an increasing number of stimulus pulses, from 1 to 4, at a constant IPI. It was demonstrated that modulations of AHP parameters after 2 pulses depended on the IPI, whereas the most significant changes in these parameters were found after the application of 2 or 3 stimuli in a series. The authors propose that changes in the AHP parameters have functional significance for motoneuronal firing pattern and therefore for motor unit force development during tetanic contractions.     

‘There is a Time to be Born and a Time to Die’ (Ecclesiastes 3:2a): Jewish Perspectives on Euthanasia

Reviewing the publications of prominent American rabbis who have (extensively) published on Jewish biomedical ethics, this article highlights Orthodox, Conservative and Reform opinions on a most pressing contemporary bioethical issue: euthanasia. Reviewing their opinions against the background of the halachic character of Jewish (biomedical) ethics, this article shows how from one traditional Jewish textual source diverse, even contradictory, opinions emerge through different interpretations. In this way, in the Jewish debate on euthanasia the specific methodology of Jewish (bio)ethical reasoning comes forward as well as a diversity of opinion within Judaism and its branches.     

Children's time production for concurrent nontemporal motor tasks

An internal clock model has often been used to explain disruptions in timing production that occur when temporal and nontemporal tasks are performed simultaneously. In this study, participants' ability to walk 8 m in 8 sec. while executing various secondary concurrent nontemporal tasks was assessed for 16 children enrolled in sports at school. Children participated in six trials under five randomized task conditions involving different coordinative and cognitive workloads. The duration of timing production increased as the attention requirements or cognitive demands placed upon the completion of the task increased. However, participants also showed learning of timing over the six trials. Significant differences were found between the timing task and the concurrent nontemporal tasks depending on the difficulty and cognitive load of the secondary tasks. Results are discussed using attention models of time estimation and production.