Biomedical subjects

Harold Bekkering

Publications and source records attributed to Harold Bekkering.

At least 19 recordsLinked to original sources

PubMed2006

Impaired motor imagery in right hemiparetic cerebral palsy.

It is generally assumed that movements of a part of the body (e.g., hands) are simulated in motor imagery (MI) tasks. This is evidenced by a linear increase in reaction time as a function of the angular rotation of the stimulus. Under the assumption that MI plays a critical role for anticipatory motor planning, which is known to be impaired in individuals with right hemiparetic cerebral palsy (right HCP; left congenital brain damage), but to a lesser extent in individuals with left HCP, we hypothesized that MI is impaired in the participants with right HCP. In the present study, 8 participants with right and 11 participants with left congenital brain damage and 9 neurologically healthy controls were presented with two MI tasks to study this supposed relation between hemispheric processes and behaviour. Participants were instructed to make a laterality judgment on the basis of displayed pictures of hands (either holding a hammer or not) presented in different orientations. For both the control group and the left HCP group, a linear increase in reaction time as a function of angle of rotation was found. Interestingly, no such relationship was observed for the right HCP group, suggesting a disorder in MI for these participants. Collectively, these findings provide new insights into the cause of the anticipatory planning deficits in right HCP individuals.

Adolescent↗

PubMed2006

Visual search near threshold: Some features are more equal than others.

While searching for objects, we combine information from multiple visual modalities. Classical theories of visual search assume that features are processed independently prior to an integration stage. Based on this, one would predict that features that are equally discriminable in single feature search should remain so in conjunction search. We test this hypothesis by examining whether search accuracy in feature search predicts accuracy in conjunction search. Subjects searched for objects combining color and orientation or size; eye movements were recorded. Prior to the main experiment, we matched feature discriminability, making sure that in feature search, 70% of saccades were likely to go to the correct target stimulus. In contrast to this symmetric single feature discrimination performance, the conjunction search task showed an asymmetry in feature discrimination performance: In conjunction search, a similar percentage of saccades went to the correct color as in feature search but much less often to correct orientation or size. Therefore, accuracy in feature search is a good predictor of accuracy in conjunction search for color but not for size and orientation. We propose two explanations for the presence of such asymmetries in conjunction search: the use of conjunctively tuned channels and differential crowding effects for different features.

Adult↗

PubMed2006

Goals and means in action observation: a computational approach.

Many of our daily activities are supported by behavioural goals that guide the selection of actions, which allow us to reach these goals effectively. Goals are considered to be important for action observation since they allow the observer to copy the goal of the action without the need to use the exact same means. The importance of being able to use different action means becomes evident when the observer and observed actor have different bodies (robots and humans) or bodily measurements (parents and children), or when the environments of actor and observer differ substantially (when an obstacle is present or absent in either environment). A selective focus on the action goals instead of the action means furthermore circumvents the need to consider the vantage point of the actor, which is consistent with recent findings that people prefer to represent the actions of others from their own individual perspective. In this paper, we use a computational approach to investigate how knowledge about action goals and means are used in action observation. We hypothesise that in action observation human agents are primarily interested in identifying the goals of the observed actor's behaviour. Behavioural cues (e.g. the way an object is grasped) may help to disambiguate the goal of the actor (e.g. whether a cup is grasped for drinking or handing it over). Recent advances in cognitive neuroscience are cited in support of the model's architecture.

Attention↗

PubMed2006

Anticipatory planning deficits and task context effects in hemiparetic cerebral palsy.

Individuals with hemiparetic cerebral palsy (HCP) display deviant motor output, predominantly on one side of the body. The question pursued here is whether HCP participants have the ability to anticipate the forthcoming perceptual-motor demands of the goal of an action sequence. Such anticipatory planning was necessary to successfully perform the tasks that were studied. In experiment I, HCP participants had to grasp a hexagonal knob with their unimpaired hand by choosing one of five possible grasping patterns (free choice) and consequently rotate it 60 degrees, 120 degrees, or 180 degrees clockwise or counterclockwise. HCP participants showed a large amount of task failures that were persistent throughout the task. These findings suggest a deficit in anticipatory planning. No such task failures were observed for the control group. In addition, the instructed degree of rotation had less effect on the selected grasping pattern for the HCP participants than for the controls. In experiment II, we investigated if HCP participants are prone to use context information that is directly available in the task, instead of planning the forthcoming perceptual-motor demands. To that aim, an arrow was inserted at one of the sides of the hexagon in a position that had no relevance for the action to be planned and executed. The location of this arrow significantly affected the grip selected in the HCP participants, but not in controls. Overall, the results suggest an anticipatory planning deficit in HCP participants that may be caused by an impairment at the motor imagery level. Consequently, as an alternative strategy, performance in HCP participants was predominantly based on information directly available in the task context.

Adolescent↗

PubMed2006

Joint action: bodies and minds moving together.

The ability to coordinate our actions with those of others is crucial for our success as individuals and as a species. Progress in understanding the cognitive and neural processes involved in joint action has been slow and sparse, because cognitive neuroscientists have predominantly studied individual minds and brains in isolation. However, in recent years, major advances have been made by investigating perception and action in social context. In this article we outline how studies on joint attention, action observation, task sharing, action coordination and agency contribute to the understanding of the cognitive and neural processes supporting joint action. Several mechanisms are proposed that allow individuals to share representations, to predict actions, and to integrate predicted effects of own and others' actions.

Attention↗

PubMed2006

Comparable mechanisms for action and language: neural systems behind intentions, goals, and means.

In this position paper we explore correspondence between neural systems for language and action starting from recent electrophysiological findings on the roles of posterior and frontal areas in goal-directed grasping actions. The paper compares the perceptual and motor organization for action and language, and discusses similarities between the impairments of apraxic and aphasic patients. Furthermore, based on the anatomical connectivity of Brodmann areas (BA) 44 and 45 separate functional roles are proposed for the two constituent parts of Broca's area. The final part of the paper includes a discussion on the role of BA 44 and neighboring areas in sequential processing for action and language.

Brain↗

PubMed2006

Semantic activation in action planning.

Four experiments investigated activation of semantic information in action preparation. Participants either prepared to grasp and use an object (e.g., to drink from a cup) or to lift a finger in association with the object's position following a go/no-go lexical-decision task. Word stimuli were consistent to the action goals of the object use (Experiment 1) or to the finger lifting (Experiment 2). Movement onset times yielded a double dissociation of consistency effects between action preparation and word processing. This effect was also present for semantic categorizations (Experiment 3), but disappeared when introducing a letter identification task (Experiment 4). In sum, our findings indicate that action semantics are activated selectively in accordance with the specific action intention of an actor.

Analysis of Variance↗

PubMed2005

Anticipatory planning of movement sequences in hemiparetic cerebral palsy.

Anticipatory planning was examined in detail for a complex object manipulation task by capitalizing on both the complexity and the number of elements in the movement sequences in seven individuals with hemiparetic cerebral palsy (HCP) and seven left-handed control participants. Participants had to grasp a hexagonal knob using one of five possible grasping patterns as quickly as possible following a starting cue (condition I), and sometimes, they had to rotate it subsequently either 60 degrees or 120 degrees clockwise or counterclockwise (condition II). In the first condition, the HCP participants appear to anticipate the comfort of the different grasping patterns before movement onset, as controls did. However, when the task consisted of more than one movement part, HCP participants did not complete their planning processes before movement onset, which was contrary to controls. Instead, the results suggest that they use a step-by-step planning strategy, that is, they planned the latter parts of a movement sequence as the movement unfolds. The results are discussed in the light of possible capacity limitations of an internal model for grip selection, and a recent model on the planning and on-line control of movement performance.

Adolescent↗

PubMed2004

Selection-for-action in visual search.

Grasping an object rather than pointing to it enhances processing of its orientation but not its color. Apparently, visual discrimination is selectively enhanced for a behaviorally relevant feature. In two experiments we investigated the limitations and targets of this bias. Specifically, in Experiment 1 we were interested to find out whether the effect is capacity demanding, therefore we manipulated the set-size of the display. The results indicated a clear cognitive processing capacity requirement, i.e. the magnitude of the effect decreased for a larger set size. Consequently, in Experiment 2, we investigated if the enhancement effect occurs only at the level of behaviorally relevant feature or at a level common to different features. Therefore we manipulated the discriminability of the behaviorally neutral feature (color). Again, results showed that this manipulation influenced the action enhancement of the behaviorally relevant feature. Particularly, the effect of the color manipulation on the action enhancement suggests that the action effect is more likely to bias the competition between different visual features rather than to enhance the processing of the relevant feature. We offer a theoretical account that integrates the action-intention effect within the biased competition model of visual selective attention.

Adult↗

PubMed2004

Modulation of activity in medial frontal and motor cortices during error observation.

We used measures of the human event-related brain potential (ERP) to investigate the neural mechanisms underlying error processing during action observation. Participants took part in two conditions, a task execution condition and a task observation condition. We found that activity in both the medial frontal cortex and the motor cortices, as measured via the error-related negativity and the lateralized readiness potential, respectively, was modulated by the correctness of observed behavior. These data suggest that similar neural mechanisms are involved in monitoring one's own actions and the actions of others.

Adult↗

PubMed2004

Object-based processes in the planning of goal-directed hand movements.

Theories in motor control suggest that the parameters specified during the planning of goal-directed hand movements to a visual target are defined in spatial parameters like direction and amplitude. Recent findings in the visual attention literature, however, argue widely for early object-based selection processes. The present experiments were designed to examine the contributions of object-based and space-based selection processes to the preparation time of goal-directed pointing movements. Therefore, a cue was presented at a specific location. The question addressed was whether the initiation of responses to uncued target stimuli could benefit from being either within the same object (object based) or presented at the same direction (space based). Experiment 1 replicated earlier findings of object-based benefits for non-goal-directed responses. Experiment 2 confirmed earlier findings of space-based benefits for goal-directed hand pointing movements. In Experiments 3 and 4, space-based and object-based manipulations were combined while requiring goal-directed hand pointing movements. The results clearly favour the notion that the selection processes for goal-directed pointing movements are primarily object based. Implications for theories on selective attention and action planning are discussed.

Attention↗

PubMed2003

Altered aiming movements in Parkinson's disease patients and elderly adults as a function of delays in movement onset.

This study investigated the effect of lengthening the time the hand remains immobilized on an aiming movement performed by Parkinson's disease (PD) patients and elderly adults, and whether visual information could compensate for the effects of delay. In Experiment One, PD patients and elderly adults kept the limb in a static position for 1, 6, or 10 s prior to movement initiation, both with and without vision of the initial limb position and the movement trajectory. Compared to elderly adults, PD patients had increased movement times and jerk scores, and exhibited shorter primary submovements that erred in initial movement direction. Lengthening the time delay increased movement time, decreased mean acceleration, and decreased the distance covered in the primary submovement for both groups. Parkinsonian patients, however, exhibited reduced length of the primary submovement across delay compared to elderly adults. Occluding vision caused the movements of PD patients to deteriorate on all measures. Although the performance of both groups was enhanced when vision was available, vision was not able to fully counteract the effects of delay in either group. In Experiment Two, participants moved to a previously viewed target to examine movement accuracy. Systematic undershooting of the target as a function of delay was found for both groups. Parkinsonian patients exhibited greater undershooting of the target after the primary submovement both with and without vision. Visual feedback reduced the effects of delay for both the elderly and PD patients. It can be inferred from the results that the decay in position sense as a function of time produces impairments in incorporating the initial limb position in motor planning process.

Aged↗

PubMed2003

Action generation and action perception in imitation: an instance of the ideomotor principle.

We review a series of behavioural experiments on imitation in children and adults that test the predictions of a new theory of imitation. Most of the recent theories of imitation assume a direct visual-to-motor mapping between perceived and imitated movements. Based on our findings of systematic errors in imitation, the new theory of goal-directed imitation (GOADI) instead assumes that imitation is guided by cognitively specified goals. According to GOADI, the imitator does not imitate the observed movement as a whole, but rather decomposes it into its separate aspects. These aspects are hierarchically ordered, and the highest aspect becomes the imitator's main goal. Other aspects become sub-goals. In accordance with the ideomotor principle, the main goal activates the motor programme that is most strongly associated with the achievement of that goal. When executed, this motor programme sometimes matches, and sometimes does not, the model's movement. However, the main goal extracted from the model movement is almost always imitated correctly.

Adult↗

PubMed2003

Time delays prior to movement alter the drawing kinematics of elderly adults.

Position sense has been found to decay as a function of the time delay the limb remains in a static position prior to movement onset. Position sense has also been found to deteriorate as a function of aging, with increased reliance on vision by the elderly. This study investigated whether the pointing kinematics of elderly adults were differentially affected by delay compared to young adults, and whether visual information could compensate for the effects of delay. Young and elderly adults kept the limb in a static position for 1, 6, or 10 s prior to movement onset, both with and without vision of the limb, initial position, and the movement trajectory. Across groups, delay resulted in increased overall movement duration, decreased peak velocity including a shorter relative time to peak velocity, with decreased distance and duration of the primary submovement. Delay and lack of vision differentially decreased distance of the primary submovement for elderly adults. Vision was able to compensate to some degree for the effects of delay across age groups. The findings provide evidence that decays in position sense as a function of time create difficulties in incorporating the initial limb position in motor planning process in elderly adults.

Adult↗

PubMed2003

To imitate or not to imitate? How the brain can do it, that is the question!

In this paper the authors discuss the most prominent views addressing the issue of how we imitate actions. It is argued that the existing theories lay along a continuum, with the direct mapping approach at one end (Butterworth, 1990; Gray, Neisser, Shapiro, & Kouns, 1991) the Active Intermodal Matching approach (Melzoff & Moore, 1997) in the middle, and the goal-directed theory (Bekkering, Wohlshäger, & Gattis, 2000) and the dual route theory (Rumiati & Tessari, 2002) at the opposite end. Interestingly the latter views can account for behaviors that cannot be explained by invoking the direct mapping or the Active Intermodal Matching approach.

Humans↗

PubMed2002

Rational imitation in preverbal infants.

Here we show that if an adult demonstrates a new way to execute a task to a group of infants aged 14 months, the children will use this action to achieve the same goal only if they consider it to be the most rational alternative. Our results indicate that imitation of goal-directed action by preverbal infants is a selective, interpretative process, rather than a simple re-enactment of the means used by a demonstrator, as was previously thought.

Adult↗

PubMed2002

Is human imitation based on a mirror-neurone system? Some behavioural evidence.

Recently, a population of neurones was discovered in the monkey's ( Macaca nemestrina) ventrolateral part of the pre-motor cortex (area F5). It is specialised for recognising object-oriented actions, regardless of whether these actions are performed or observed by the monkey. The latter observation led to the term mirror-neurones, and because these cells respond to both observed and executed actions, it seems likely that neurones of that type became co-opted during hominid evolution to serve the imitative behaviours that are so prevalent in our species. There is recent physiological evidence that Broca's area, the human ( Homo sapiens) homologue of monkey's area F5, is involved in the imitation of finger movements. However, concluding that human imitation is based on a mirror-neurone system is premature, because: (1) imitation in monkeys does not reach the same level as in humans or apes and (2) monkeys' mirror-neurones are specialised for object-oriented actions. This specialisation has not yet been demonstrated in adult humans. We investigated the role of objects in human imitation behaviour in a response time experiment. Subjects had to imitate downward movements of an index finger. In one condition, the observed finger touched one of two dots either ipsi- or contralaterally. In the other condition, the very same movements had to be imitated. However, there were no dots on the table. The presence of dots had a decisive influence on error patterns and on response times, but did not influence the movement proper. Dots specifically reduced the onset latency of ipsilateral finger movements and they specifically increased the use of the wrong finger, when contralateral movements were required. In general, results showed that objects also drive human imitation behaviour. Hence, it is very likely that imitation emerged from the mirror-neurone system of the common ancestor of monkeys and humans.

Adult↗

PubMed2002

Commentary: coordination of eye and hand in time and space.

Every day of our lives starts with a succession of actions that require eye-hand coordination. From the time we try to turn off the alarm clock and get dressed, to putting toothpaste on the brush and preparing coffee: all these goal-directed hand movements need to be coordinated with the information from the eye. When performing such simultaneous goal-directed eye and hand movements, both the time and location at which eye and hand land on the object need to be harmonized. For better localizing the alarm clock, we need to see it before we hit it. In order to use this visual information for an accurate hand movement, we need the eye to land on the same position, i.e. eye and hand both need to be on the alarm clock instead of the water glass. These two aspects, temporal and spatial coordination, have encouraged a great deal of research. On the following pages, we will summarize a number of findings on how this coordination could be achieved.

Animals↗