Understanding other people's actions: intention and attention

This study investigated the extent to which observation of an action performed by a human actor or a robotic arm may kinematically prime the performance of an observer subsequently required to perform a similar action. In Experiment 1, an actor reached for a target presented in isolation or flanked by a distractor object. Subsequently, an observer was required to perform a similar action toward the target object, but always in the absence of the distractor. The kinematics of both the human actor and the observer were affected by the presence of the distractor. Unexpectedly, similar effects were found in the observer's kinematics during the trials in which the actor was seated in front of the observer but no action was demonstrated (catch trials). Results from 4 subsequent experiments suggest that the motor intentions of the actor can be inferred by monitoring his or her gaze. To support this conclusion, results are discussed in terms of recent work spanning many disciplines involved in combining gaze direction and body movements.     

Different action patterns for cooperative and competitive behaviour

The aim of the present study is to elucidate the influence of context on the kinematics of the reach-to-grasp movement. In particular, we consider two basic modes of social cognition, namely cooperation and competition. In two experiments kinematics of the very same action - reaching-to-grasp a wooden block - were analyzed in two different contexts provided by a cooperative task and competitive task. For the 'cooperation' tasks two participants were required to reach and grasp their respective objects and to cooperate to join the two objects in specific configurations in the middle of the working surface. For the 'competition' tasks, the two participants had to compete to place their own object first in the middle of the working surface. Results revealed specific kinematic patterns for cooperation and competition which were distinct from similar actions performed by each participant in isolation. Further, during the cooperation tasks, a high level of correlation between key kinematical parameters of the two participants was found. In accordance with evidence from neuroimaging, developmental and social psychology our results suggest the existence of motor patterns which reflect the intention to act in a social context.     

Corticospinal excitability during the observation of social behavior

Evidence suggests that the observation of an action induces in the observers an enhancement of motor evoked potentials (MEPs) recorded by the observer’s muscles corresponding to those involved in the observed action. Although this is a well-studied phenomenon, it remains still unclear how the viewer’s motor facilitation is influenced by the social content characterizing the observed scene. In the present study we investigated the facilitation of the corticospinal system during the observation of either an action that does not imply a social interaction (i.e., an actor throwing a ball against a wall), or an action which implies a social interaction (i.e., an actor passing a ball to a partner). Results indicate that MEPs amplitude is enhanced during the observation of a social rather than an individual action. We contend that the increase in MEPs activation might reflect an enhancement of the simulative activity stemming from the mirror system during the observation of social interactions. Altogether these findings show that the human corticospinal system is sensitive to social interactions and may support the role of the mirror neurons system in social cognition.     

Testing the effects of end-goal during reach-to-grasp movements in Parkinson’s disease

Previous evidence suggests that hand shaping during reaching is modulated by the presence and the nature of the end-goal following object’s grasp. Here we test whether such modulation is maintained in Parkinson’s disease (PD). Six participants with PD and six healthy participants took part in the study. Participants were requested to reach towards a bottle filled with water, and then: (1) grasp it without performing any subsequent action; (2) grasp it and place it accurately on a target area; (3) grasp it and pour its contents within a container. The results showed that participants shaped their hand differently depending on the presence or absence of an action following object’s grasp. However, the request to perform an action after grasp determined a modulation of hand kinematics which was delayed for PD than for control participants. Further, whereas for control participants the nature of the end-goal determined a modulation of hand shaping, for PD patients such modulation was not evident. Data are discussed in terms of the role played by basal ganglia in implementing anticipatory mechanisms for the control of manipulative activities. We contend that in PD patients these mechanisms are not totally compromised, but their implementation depends on the action information that has to be anticipated.     

Mirror neurons in humans: consisting or confounding evidence?

The widely known discovery of mirror neurons in macaques shows that premotor and parietal cortical areas are not only involved in executing one's own movement, but are also active when observing the action of others. The goal of this essay is to critically evaluate the substance of functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies whose aim has been to reveal the presence of a parallel system in humans. An inspection of this literature suggests that there is relatively weak evidence for the existence of a circuit with 'mirror' properties in humans, such as that described in monkeys.     

Object-centred orienting of attention

Abstract

In the present study two experiments are reported in which the subjects were presented on a computer screen with a two-dimensional line drawing that is perceived as a three-dimensionalobject (i.e. a cube). The cube could be seen as stationary, as rotating about the y-axis (Experiment 1A), or as rotating about the x-axis (Experiment 1B). The subject's attention was directed by a visual precue to a vertex of the cube. As the cube rotated, the precued location moved in viewer-centred co-ordinatesm, but the local feature of the cube that had been precued (i.e. a given vertex) did not move in object-centred co-ordinates. The imperative stimulus was presented at the precued location (valid trials) or at an uncued location (invalid trials). Precued and uncued locations were determined in object-centred coordinates. The subjects were required to signal detection of the imperative stimulus by pressing the space bar on the computer keyboard. There were also control conditions in which the procedure was identical, but the cube was not visible. When the cube was visible, valid trials were faster than invalid trials, regardless of whether it was seen as stationary or rotating. It was concluded that the subjects could allocate spatial attention in object-centred co-ordinates. There wer also indications that responses for invalid trials were faster when the imperative stimulus was presented on the same face as the precue than when it was presented on the opposite face.     

The Simon Effect in Action: Planning and/or On‐Line Control Effects?

Choice reaction tasks are performed faster when stimulus location corresponds to response location (Simon effect). This spatial stimulus–response compatibility effect affects performance at the level of action planning and execution. However, when response selection is completed before movement initiation, the Simon effect arises only at the planning level. The aim of this study was to ascertain whether when a precocious response selection is requested, the Simon effect can be detected on the kinematics characterizing the online control phase of a non‐ballistic movement. Participants were presented with red or green colored squares, which could appear on the right, left, above, or below a central cross. Depending on the square's color, participants had to release one of two buttons (right/left), then reach toward and press a corresponding lateral pad. We found evidence of the Simon effect on both action planning and on‐line control. Moreover, the investigation of response conflict at the level of previous trials (i.e., n?1), a factor that might determine interference at the level of the current response, revealed a conflict adaptation process across trials. Results are discussed in terms of current theories concerned with the Simon effect and the distinction between action planning and control.     

The effects of abrupt onset of 2-D and 3-D distractors on prehension movements

This article includes two experiments aimed at investigating how two-dimensional (2-D) and threedimensional (3-D) distractors affect the kinematics of prehension and aiming movements in order to understand the attentional processes involved in visuomotor control. In Experiment 1, subjects grasped large targets in the presence of both large and small 3-D distractors and their corresponding 2-D photographs. The distractors appeared for either 10 sec or appeared simultaneously with the target presentation. It was found that reach and grasp kinematics were influenced primarily by the small, suddenly appearing 3-D distractors. In Experiment 2, the purpose was to examine the conclusion that competition between objects (target and distractor) is related to the behavioral goal of the task. Experiment 2 is a replication of Experiment 1, with the exception that pointing movements were made instead of grasping movements. Results show that both 3-D and 2-D distractors interfered with pointing kinematics, supporting the hypothesis that attentional mechanisms are related to the goal of the task.     

Orienting the Finger Opposition Space during Prehension Movements

Two experiments are reported that examined the act of prehension when subjects were asked to grasp with their thumb and index finger pads an elongated object resting horizontally on a surface and placed at different orientations with respect to the subject. In Experiment 1, the pad opposition preferences were determined for the six angles of orientation examined. For angles of 90° (object parallel to frontal plane) or less, no rotation of the wrist (pronation) was used; for angles 110° or greater, pronation was systematically employed to reorient the finger opposition space. Only one angle, 100°, produced any evidence of ambiguity in how to grasp the object: Approximately 60% of these grasps involved pronation and 40% did not.

Using the foregoing grasp preference data, in Experiment 2 we examined the kinematics of the wrist and elbow trajectories during prehension movements directed at an object in different orientations. Movement time, time to peak acceleration, velocity, and deceleration were measured. No kinematic differences were observed when the object orientation either required (110°) or did not require (80°) a pronation. By contrast, if the orientation was changed at the onset of the movement, such that an unpredicted pronation had to be introduced to achieve the grasp, kinematics were affected: Movement time was increased, and the time devoted to deceleration was lengthened.

These data are interpreted as evidence that when natural prehension occurs, pronation can be included in the motor plan without affecting the movement kinematics. When constraints are imposed on the movement execution as a consequence of a perturbation, however, the introduction of a pronation component requires kinematic rearrangement.