The end-state comfort effect facilitates joint action

Motor experts can accurately predict the future actions of others by observing their movements. This report describes three experiments that investigate such predictions in everyday object manipulations and test whether these predictions facilitate responses to the actions of others. Observing video excerpts showing an actor reaching for a vertically mounted dial, participants in Experiment 1 needed to predict how the actor would rotate it. Their predictions were specific to the direction and extent of the dial rotation and improved proportionate to the length of the video clip shown. Testing whether such predictions facilitate responses, in the subsequent experiments responders had to undo an actor's actions, back-rotating a dial (Exp 2) and a bar (Exp 3). The responders' actions were initiated faster when the actors' movements obeyed the so-called end-state comfort principle than when they did not. Our experiments show that humans exploit the end-state comfort effect to tweak their predictions of the future actions of others. The results moreover suggest that the precision of these predictions is mediated by perceptual learning rather than by motor simulation.     

The continuous end-state comfort effect: weighted integration of multiple biases

The grasp orientation when grasping an object is frequently aligned in anticipation of the intended rotation of the object (end-state comfort effect). We analyzed grasp orientation selection in a continuous task to determine the mechanisms underlying the end-state comfort effect. Participants had to grasp a box by a circular handle—which allowed for arbitrary grasp orientations—and then had to rotate the box by various angles. Experiments 1 and 2 revealed both that the rotation’s direction considerably determined grasp orientations and that end-postures varied considerably. Experiments 3 and 4 further showed that visual stimuli and initial arm postures biased grasp orientations if the intended rotation could be easily achieved. The data show that end-state comfort but also other factors determine grasp orientation selection. A simple mechanism that integrates multiple weighted biases can account for the data.     

An explanation of orthogonal S-R compatibility effects that vary with hand or response position: the end-state comfort hypothesis

This study presents an explanation of orthogonal stimulus-response compatibility (SRC) effects that vary with hand or response location: the end-state comfort hypothesis. It posits that responses are spatially transformed and cognitively mapped onto the stimulus dimension according to relative hand posture, thereby mediating the pattern of facilitation and interference in response selection. In the first three experiments, we investigated the eccentricity effect, finding that responses by the left hand in left hemispace are faster with up-left/down-right mapping while responses by the right hand in right hemispace are faster with up-right/down-left mapping (Michaels & Schilder, 1991, Experiment 1). The endstate comfort hypothesis correctly predicted that the eccentricity effect occurred irrespective of the relative position of the stimulus and response device in the sagittal plane (Experiments 1 and 2), and that it reversed when the stimulus-response set was reversed, regardless of the relative position of the stimulus and response device in the fronto-parallel plane (Experiments 2 and 3). Experiment 4 shows a new orthogonal SRC effect that was predicted by the end-state comfort hypothesis. Our results are inconsis tent with other explanations, such as the virtual-lines hypothesis and the salient-features hypothesis.     

Choice of end-state comfort is dependent upon the time spent at the beginning-state and the precision requirement of the end-state

Choice of posture while grasping an object typically depends upon several factors including the time spent in that posture, what postures were held prior to choosing that posture, and the precision required by the posture. The purpose of this study was to test choice of end-state thumb-up posture based on time spent at the beginning-state and the precision requirement of the end-state. To determine choice of thumb-up based on time or precision, we varied how long a subject had to hold the beginning state before moving an object to an end location. We made end-state precision either small or large and eliminated the precision needed to stand the object up at the end of the movement. A choice between “comfort” at the beginning or precision at the end-state would be demanded by the conditions with long beginning-state hold times and high precision demands. We aimed to determine which aspect of movement was of greater importance to individuals, overall “comfort” or precision. When the requirement was to hold the initial grasp longer, and the end-target was large, we predicted that we would see more thumb-up postures adopted at the beginning state. When the final placement was small and the initial posture was not constrained, we predicted we would see thumb-up postures adopted at the end state. On average, we found that, as beginning-state grasp time increased, more individuals chose beginning-state thumb-up postures. Perhaps, not surprisingly, we found distinct individual differences within our sample. Some individuals seemed to choose beginning-state thumb-up postures nearly 100% of the time, while other individuals chose end-state thumb-up postures nearly 100% of the time. Both the time spent in a posture and its precision requirements influenced planning, but not necessarily in a systematic way.     

End in view: Joint end-state comfort depends on gaze and extraversion

This study investigated how humans adapt to a partner's movement in a joint pick-and-place task and examined the role of gaze behavior and personality traits in adapting to a partner. Two participants sitting side-by-side transported a cup from one end of a table to the other. The participant sitting on the left (the agent) moved the cup to an intermediate position from where the participant sitting on the right (the partner) transported it to a goal position with varying orientations. Hand, finger, cup movements and gaze behavior were recorded synchronously via motion tracking and portable eye tracking devices. Results showed interindividual differences in the extent of the agents' motor adaptation to the joint action goal, which were accompanied by differences in gaze patterns. The longer agents directed their gaze to a cue indicating the goal orientation, the more they adapted the rotation of the cup's handle when placing it at the intermediate position. Personality trait assessment showed that higher extraverted tendencies to strive for social potency went along with more adaptation to the joint goal. These results indicate that agents who consider their partner's end-state comfort use their gaze to gather more information about the joint action goal compared to agents who do not. Moreover, the disposition to enjoy leadership and make decisions in interpersonal situations seems to play a role in determining who adapts to a partner's task in joint action.     

Optimal versus heuristic planning of object manipulations: A review and a computational model of the continuous end-state comfort effect

Human beings select actions that facilitate the execution of later actions. For example, humans tend to select grasps that ensure that forthcoming object manipulations end in a comfortable posture (“end-state comfort effect”). Basic experimental results and their explanation within the optimal control framework are reviewed. I conclude that the discrete grasp selection tasks, which are commonly used to study anticipatory planning, leave room for alternative explanations. Moreover, the results of seven experiments employing a continuous grasp selection task seem incompatible with the optimal control (of end-state comfort) account. I introduce the weighted integration of multiple biases (WIMB) model, which accounts for many aspects of the selection of human grasp orientations in continuous tasks. Additionally, it accounts for the precision effect and hysteresis effect. The model shows that the brain may rely on a simple heuristic and does not actually has to anticipate the end-state of a movement to select effective grasps for object manipulations.     

The influence of time constraints on posture choices during an end-state comfort task

People adopt comfortable postures for the end states of motor actions (end-state comfort; Rosenbaum & Jorgensen, 1992). The choice to end comfortably often elicits adoption of uncomfortable beginning states, demonstrating that a sequence of movement is planned in advance of movement onset. Many factors influence the choice of comfortable end-state postures including the greater precision and speed afforded by postures at joint angle mid-ranges (Short & Cauraugh, 1999). To date, there has been little evaluation of the hypothesis that postures are chosen based on minimizing the time spent in uncomfortable postures. The aim of this experiment was to examine how the relative time required to hold beginning and end-state postures influenced the choice of posture. Participants moved a two-toned wooden dowel from one location to another with the requirement to grasp the object and place a specified color down. Participants completed four conditions where no postures were held, only one posture was held, or both postures were held. We predicted more thumb-up postures for positions held longer regardless of whether these postures were at the end or beginning state. Results verified that the constraint of holding the initial posture led to decreased end-state comfort supporting the hypothesis that estimation of time spent in postures is an important constraint in planning. We also note marked individual differences in posture choices, particularly when the object was moved to the left.     

Monkey see, monkey plan, monkey do: the end-state comfort effect in cotton-top tamarins (Saguinus oedipus)

The way human adults grasp objects is typically influenced by their knowledge of what they intend to do with the objects. This influence is reflected in the end-state comfort effect: Actors adopt initially uncomfortable postures to accommodate later task demands. Although many experiments have demonstrated this effect, to the best of our knowledge its phylogenetic roots have not been investigated. In two experiments, we tested whether 9 cotton-top tamarin monkeys would show the end-state comfort effect. We did so by presenting the monkeys with a small cup containing a marshmallow. The cup was suspended in different orientations. The monkeys inhibited their natural grasping tendencies and adopted unusual grasping postures to accommodate subsequent task requirements, thus demonstrating the end-state comfort effect. This outcome provides evidence for more sophisticated motor planning than has previously been ascribed to this and related species.     

The influence of initial and final precision on motor planning: individual differences in end-state comfort during unimanual grasping and placing

People will often grasp an object with an uncomfortable initial grasp if this affords more comfort at the end of the movement. The authors' primary objective was to examine whether grasp planning is influenced by precision demands at the start and end of the movement. Twenty right-handed individuals performed a unimanual grasping and placing task in which the precision requirements at the start and end of the movement were either identical (low initial and final precision, high initial and final precision) or different (low initial and high final precision, high initial and low final precision). The major finding to emerge was the presence of individual differences. 50% of participants changed their initial grasps based on the precision requirements of the task, and were more likely to satisfy end-state comfort when the final precision requirements were high than when they were low. In contrast, 50% of participants generally planned their movements to satisfy end-state comfort (regardless of precision requirements). The authors hypothesized that the former group of participants was sensitive to the precision demands of the task, and participants planned their grips in accordance with these demands. In contrast, the latter group of participants reduced the cognitive costs by using previously successful grasp plans.     

The differentiation hypothesis and the Flynn effect

Many studies have shown that IQs have been increasing over the last half century. These increases have come to be known as "the Flynn effect". The "Flynn effect" represents a difference on ability-level between groups of the same age but different cohort. The ability-level differentiation hypothesis represents a difference on the relevance of cognitive factors between groups of high and low ability. Hence, it should be possible to imitate the ability-level differentiation effect by comparing groups of the same age but different cohort. The indifferentiation hypothesis represents no differences on the relevance of cognitive abilities in all age groups within the same cohort. The aim of the present study is to test the relationships between these phenomena. For this purpose we analyzed the American standardisation samples of the WISC, WISC-R and WISC-III. Results support the link between the Flynn effect and the differentiation hypothesis. Also, reported evidence replicate previous findings supporting the indifferentiation hypothesis. Implications for the assessment of the intelligence are discussed.     

The partial-reinforcement extinction effect and the contingent-sampling hypothesis

The partial-reinforcement extinction effect (PREE) implies that learning under partial reinforcements is more robust than learning under full reinforcements. While the advantages of partial reinforcements have been well-documented in laboratory studies, field research has failed to support this prediction. In the present study, we aimed to clarify this pattern. Experiment 1 showed that partial reinforcements increase the tendency to select the promoted option during extinction; however, this effect is much smaller than the negative effect of partial reinforcements on the tendency to select the promoted option during the training phase. Experiment 2 demonstrated that the overall effect of partial reinforcements varies inversely with the attractiveness of the alternative to the promoted behavior: The overall effect is negative when the alternative is relatively attractive, and positive when the alternative is relatively unattractive. These results can be captured with a contingent-sampling model assuming that people select options that provided the best payoff in similar past experiences. The best fit was obtained under the assumption that similarity is defined by the sequence of the last four outcomes.     

Evaluation apprehension,hypothesis awareness,and the weapons effect

The present study was designed to extend Turner and Simons' (1974) investigation of possible experimental artifacts in aggression research. Employing a 2 × 2 × 2 factorial design, 60 male subjects were given either a low or high evaluation apprehension treatment, and then were either exposed or not exposed to weapons in an otherwise close replication of the seven shock-unassociated weapons condition of Berkowitz and LePage (1967). Based on an objectively worded postexperimental questionnaire, subjects were classified as being aware or not aware that the procedures were designed to make them give more shock to their partners. The findings, which were consistent with the analysis of Berkowitz (1974) and Turner and Simons (1974), indicated that the weapons-no weapons comparison was significant only for non-apprehensive, nonaware subjects. The results were interpreted as suggesting that evaluation apprehension, hypothesis awareness, and sophistication in aggression experiments may produce inhibitions which can modify the effects of experimental manipulations.     

The word frequency effect for recognition memory and the elevated-attention hypothesis

Empirical tests were conducted on the elevated-attention hypothesis that low-frequency (LF) words are better recognized than high-frequency (HF) words because LF words attract more attention than do HF words (e.g., Glanzer & Adams, 1990). The elevated-attention hypothesis predicts that the hit rate advantage for LF words should be reduced by increases in attentional strain at study. We first tested this prediction in two experiments by varying the amount of experimenter-controlled study time (on the basis of the assumption that a decrease in study time would reduce the amount of resources available for studying a word). The elevated-attention hypothesis was confirmed, but only when words were studied for relatively short durations. This finding led us to formulate an early-phase elevated-attention hypothesis that proposes that more attentional resources are allocated to LF words than to HF words only during the early phase of encoding (which produces the LF hit rate advantage in subsequent recognition) and that the allocation of attentional resources during the late phase of encoding is not greater for LF words than for HF words. An additional empirical test of this revised hypothesis was conducted: Experimenter-controlled study time and the composition of the to-be-remembered pairs of words were varied orthogonally. The results confirmed the early-phase elevated-attention hypothesis.     

On the Bradley hypothesis concerning agrammatism: the nonword-interference effect

In 1980, D. C. Bradley, M. F. Garrett, and E. B. Zurif (in D. Caplan (Ed.), Biological studies of mental processes, Cambridge, MA: MIT Press) have proposed a lexical hypothesis on agrammatism. The theoretical background of this hypothesis is described. Then two experiments are reported with normal speakers on the so-called nonword-interference effect that has been one of the two major sources of experimental evidence for this hypothesis. The first experiment replicates the original finding that the interference effect is found when the nonword starts with a content word but not when it starts with a function word. In the second experiment, it is shown that this contrast is due to an artifact of the composition of the word list. When this list contains both content and function words, rather than only content words--as in Bradley's experiments and our Experiment I--both content and function nonwords show an equally sized interference effect. The consequences for the lexical hypothesis are discussed.     

Design controversies and the generation effect: Support for an item-order hypothesis

We performed three experiments to investigate an earlier finding of Nairne, Riegler, and Serra (1991) that item generation disrupts the long-term retention of serial order. Experiment 1 demonstrated a clear advantage of reading over generating on a reconstruction test when reading and generating occurred in pure, but not mixed, lists. Experiment 2 showed that the standard generate advantage is seen in free recall of mixed, but not pure, lists, even when recall is immediately followed by reconstruction of serial order of the same items. Experiment 3 replicated Experiment 1, but with the use of an incidental learning procedure. The results of all three experiments are consistent with the claim that generation has dissociative effects on item and order memory; moreover, these dissociative effects help to explain design controversies-in the -generation effect literature.     

The bigram trough hypothesis and the syllable number effect in lexical decision

There has been an increasing volume of evidence supporting the role of the syllable in various word processing tasks. It has, however, been suggested that syllable effects may be caused by orthographic redundancy. In particular, it has been proposed that the presence of bigram troughs at syllable boundaries cause what are seen as syllable effects. We investigated the bigram trough hypothesis as an explanation of the number of syllables effect for lexical decision in five-letter words and nonwords from the British Lexicon Project. The number of syllables made a significant contribution to prediction of lexical decision times along with word frequency and orthographic similarity. The presence of a bigram trough did not. For nonwords, the number of syllables made a significant contribution to prediction of lexical decision times only for nonwords with relatively long decision times. The presence of a bigram trough made no contribution. The evidence presented suggests that the bigram trough cannot be an explanation of the syllable number effect in lexical decision. A comparison of the results from words and nonwords is interpreted as providing some support for dual-route models of reading.     

The action effect: Support for the biased competition hypothesis

The action effect refers to the finding that faster response times are found when a previously responded to stimulus contains a target item than when it serves as a distracting item in a visual search. The action effect has proven robust to a number of perceptual and attentional manipulations, but the mechanisms underlying it remain unclear. In the current study, we present two experiments investigating a possible underlying mechanism of the action effect; that responding to a stimulus increases its attentional weight causing the system to prioritize it in the visual search. In Experiment 1, we presented the search stimulus in isolation and found no evidence of an action effect. Thus, when there was no requirement for prioritization, there was no action effect. In Experiment 2, we tested whether stimulus-based priming (rather than the action) can account for the observed validity effects. We found no evidence of a priming effect when there were never any actions. These findings are consistent with the biased competition hypothesis and provide a framework for explaining the action effect while also ruling out other potential explanations such as event file updating.