Does Parkinson’s disease affect judgement about another person’s action?

The lateralized effects of Parkinson's Disease on motor imagery: Evidence from mental chronometry

Alterations to the content of action representations may contribute to the movement challenges that characterize Parkinson's Disease (PD). One way to investigate action representations is through motor imagery. As PD motor symptoms typically have a unilateral onset, disease-related deficits related to action representations may follow a similarly lateralized pattern. The present study examined if temporal accuracy of motor imagery in individuals with PD differed according to the side of the body involved in the task. Thirty-eight participants with PD completed a mental chronometry task using their more affected and less affected side. Participants had significantly shorter mental versus physical movement times for the more affected. Higher imagery vividness in the kinaesthetic domain predicted shorter mental versus physical movement times for the more affected side, as did lower imagery vividness in the visual domain and poorer cognitive function. These results indicate that people with PD imagine movements differently when the target actions their more affected versus less affected side. It is additionally possible that side-specific deficits in the accurate processing of kinaesthetic information lead to an increased reliance on visual processes and cognitive resources to successfully execute motor imagery involving the more affected side.

Development of visual perception of others' actions: Children's judgment of lifted weight

Humans are excellent at perceiving different features of the actions performed by others. For instance, by viewing someone else manipulating an unknown object, one can infer its weight–an intrinsic feature otherwise not directly accessible through vision. How such perceptual skill develops during childhood remains unclear. To confront this gap, the current study had children (N:63, 6–10 years old) and adults (N:21) judge the weight of objects after observing videos of an actor lifting them. Although 6-year-olds could already discriminate different weights, judgment accuracy had not reached adult-like levels by 10 years of age. Additionally, children’s stature was a more reliable predictor of their ability to read others’ actions than was their chronological age. This paper discusses the results in light of a potential link between motor development and action perception.

Action observation produces motor resonance in Parkinson's disease

Observation of movement activates the observer's own motor system, influencing the performance of actions and facilitating social interaction. This motor resonance is demonstrated behaviourally through visuomotor priming, whereby response latencies are influenced by the compatibility between an intended action and an observed (task-irrelevant) action. The impact of movement disorders such as Parkinson's disease (PD) on motor resonance is unclear, as previous studies of visuomotor priming have not separated imitative compatibility (specific to human movement) from general stimulus-response compatibility effects. We examined visuomotor priming in 23 participants with mild-to-moderate PD and 24 healthy older adults, using a task that pitted imitative compatibility against general stimulus-response compatibility. Participants made a key press after observing a task-irrelevant moving human finger or rectangle that was either compatible or incompatible with their response. Imitative compatibility effects, rather than general stimulus-response compatibility effects, were found specifically for the human finger. Moreover, imitative compatibility effects did not differ between groups, indicating intact motor resonance in the PD group. These findings constitute the first unambiguous demonstration of imitative priming in both PD and healthy ageing, and have implications for therapeutic techniques to facilitate action, as well as the understanding of social cognition in PD.

Probing links between action perception and action production in Parkinson's disease using Fitts' law

Information on how the subcortical brain encodes information required to execute actions or to evaluate others' actions remains scanty. To clarify this link, Fitts'-law tasks for perception and execution were tested in patients with Parkinson's disease (PD). For the perception task, participants were shown apparent motion displays of a person moving their arm between two identical targets and reported whether they judged that the person could realistically move at the perceived speed without missing the targets. For the motor task, participants were required to touch the two targets as quickly and accurately as possible, similarly to the person observed in the perception task. In both tasks, the PD group exhibited, or imputed to others, significantly slower performances than those of the control group. However, in both groups, the relationships of perception and execution with task difficulty were exactly those predicted by Fitts' law. This suggests that despite dysfunction of the subcortical region, motor simulation abilities reflected mechanisms of compensation in the PD group. Moreover, we found that patients with PD had difficulty in switching their strategy for estimating others' actions when asked to do so.

Are Older Adults Less Embodied? A Review of Age Effects through the Lens of Embodied Cognition

Embodied cognition is a theoretical framework which posits that cognitive function is intimately intertwined with the body and physical actions. Although the field of psychology is increasingly accepting embodied cognition as a viable theory, it has rarely been employed in the gerontological literature. However, embodied cognition would appear to have explanatory power for aging research given that older adults typically manifest concurrent physical and mental changes, and that research has indicated a correlative relationship between such changes. The current paper reviews age-related changes in sensory processing, mental representation, and the action-perception relationship, exploring how each can be understood through the lens of embodied cognition. Compared to younger adults, older adults exhibit across all three domains an increased tendency to favor visual processing over bodily factors, leading to the conclusion that older adults are less embodied than young adults. We explore the significance of this finding in light of existing theoretical models of aging and argue that embodied cognition can benefit gerontological research by identifying further factors that can explain the cause of age-related declines.

Motor-Evoked Potentials in the Lower Back Are Modulated by Visual Perception of Lifted Weight

Facilitation of the primary motor cortex (M1) during the mere observation of an action is highly congruent with the observed action itself. This congruency comprises several features of the executed action such as somatotopy and temporal coding. Studies using reach-grasp-lift paradigms showed that the muscle-specific facilitation of the observer’s motor system reflects the degree of grip force exerted in an observed hand action. The weight judgment of a lifted object during action observation is an easy task which is the case for hand actions as well as for lifting boxes from the ground. Here we investigated whether the cortical representation in M1 for lumbar back muscles is modulated due to the observation of a whole-body lifting movement as it was shown for hand action. We used transcranial magnetic stimulation (TMS) to measure the corticospinal excitability of the m. erector spinae (ES) while subjects visually observed the recorded sequences of a person lifting boxes of different weights from the floor. Consistent with the results regarding hand action the present study reveals a differential modulation of corticospinal excitability despite the relatively small M1 representation of the back also for lifting actions that mainly involve the lower back musculature.

A third-person perspective on co-speech action gestures in Parkinson's disease

A combination of impaired motor and cognitive function in Parkinson's disease (PD) can impact on language and communication, with patients exhibiting a particular difficulty processing action verbs. Co-speech gestures embody a link between action and language and contribute significantly to communication in healthy people. Here, we investigated how co-speech gestures depicting actions are affected in PD, in particular with respect to the visual perspective—or the viewpoint – they depict. Gestures are closely related to mental imagery and motor simulations, but people with PD may be impaired in the way they simulate actions from a first-person perspective and may compensate for this by relying more on third-person visual features. We analysed the action-depicting gestures produced by mild-moderate PD patients and age-matched controls on an action description task and examined the relationship between gesture viewpoint, action naming, and performance on an action observation task (weight judgement). Healthy controls produced the majority of their action gestures from a first-person perspective, whereas PD patients produced a greater proportion of gestures produced from a third-person perspective. We propose that this reflects a compensatory reliance on third-person visual features in the simulation of actions in PD. Performance was also impaired in action naming and weight judgement, although this was unrelated to gesture viewpoint. Our findings provide a more comprehensive understanding of how action-language impairments in PD impact on action communication, on the cognitive underpinnings of this impairment, as well as elucidating the role of action simulation in gesture production.

Embodied cognition of aging

Embodiment is revolutionizing the way we consider cognition by incorporating the influence of our body and of the current context within cognitive processing. A growing number of studies which support this view of cognition in young adults stands in stark contrast with the lack of evidence in favor of this view in the field of normal aging and neurocognitive disorders. Nonetheless, the validation of embodiment assumptions on the whole spectrum of cognition is a mandatory step in order for embodied cognition theories to become theories of human cognition. More pragmatically, aging populations represent a perfect target to test embodied cognition theories due to concomitant changes in sensory, motor and cognitive functioning that occur in aging, since these theories predict direct interactions between them. Finally, the new perspectives on cognition provided by these theories might also open new research avenues and new clinical applications in the field of aging. The present article aims at showing the value and interest to explore embodiment in normal and abnormal aging as well as introducing some potential theoretical and clinical applications.

Auditory Clicks Distort Perceived Velocity but Only When the System has to Rely on Extraretinal Signals

Previous work has found that repetitive auditory stimulation (click trains) increases the subjective velocity of subsequently presented moving stimuli. We ask whether the effect of click trains is stronger for retinal velocity signals (produced when the target moves across the retina) or for extraretinal velocity signals (produced during smooth pursuit eye movements, when target motion across the retina is limited). In Experiment 1, participants viewed leftward or rightward moving single dot targets, travelling at speeds from 7.5 to 17.5 deg/s. They estimated velocity at the end of each trial. Prior presentation of auditory click trains increased estimated velocity, but only in the pursuit condition, where estimates were based on extraretinal velocity signals. Experiment 2 generalized this result to vertical motion. Experiment 3 found that the effect of clicks during pursuit disappeared when participants tracked across a visually textured background that provided strong local motion cues. Together these results suggest that auditory click trains selectively affect extraretinal velocity signals. This novel finding suggests that the cross-modal integration required for auditory click trains to influence subjective velocity operates at later stages of processing.

Does that look heavy to you? Perceived weight judgment in lifting actions in younger and older adults

When interpreting other people's movements or actions, observers may not only rely on the visual cues available in the observed movement, but they may also be able to "put themselves in the other person's shoes" by engaging brain systems involved in both "mentalizing" and motor simulation. The ageing process brings changes in both perceptual and motor abilities, yet little is known about how these changes may affect the ability to accurately interpret other people's actions. Here we investigated the effect of ageing on the ability to discriminate the weight of objects based on the movements of actors lifting these objects. Stimuli consisted of videos of an actor lifting a small box weighing 0.05-0.9 kg or a large box weighting 3-18 kg. In a four-alternative forced-choice task, younger and older participants reported the perceived weight of the box in each video. Overall, older participants were less sensitive than younger participants in discriminating the perceived weight of lifted boxes, an effect that was especially pronounced in the small box condition. Weight discrimination performance was better for the large box compared to the small box in both groups, due to greater saliency of the visual cues in this condition. These results suggest that older adults may require more salient visual cues to interpret the actions of others accurately. We discuss the potential contribution of age-related changes in visual and motor function on the observed effects and suggest that older adults' decline in the sensitivity to subtle visual cues may lead to greater reliance on visual analysis of the observed scene and its semantic context.

Impaired visual perception of hurtful actions in patients with chronic low back pain

Visually presented biological motion stimuli activate regions in the brain that are also related to musculo-skeletal pain. We therefore hypothesized that chronic pain impairs the perception of visually presented actions that involve body parts that hurt. In the first experiment, chronic back pain (CLBP) patients and healthy controls judged the lifted weight from point-light biological motion displays. An actor either lifted an invisible container (5, 10, or 15 kg) from the floor, or lifted and manipulated it from the right to the left. The latter involved twisting of the lower back and would be very painful for CLBP patients. All participants recognized the displayed actions, but CLBP patients were impaired in judging the difference in handled weights, especially for the trunk rotation. The second experiment involved discrimination between forward and backward walking. Here the patients were just as good as the controls, showing that the main result of the first experiment was indeed specific to the sensory aspects of the task, and not to general impairments or attentional deficits. The results thus indicate that the judgment of sensorimotor aspects of a visually displayed movement is specifically affected by chronic low back pain.

Representation of action in Parkinson's disease: imagining, observing, and naming actions

People with Parkinson's disease (PD) exhibit slowed movements and difficulty in initiating movements. This review addresses the issue of whether or not cognitive representations of actions in PD are affected, alongside these motor problems. In healthy people, the motor system can be involved in tasks such as observing a graspable object or another person's action, or imagining and naming actions, in the absence of overt movement. As described in this review, the fact that the slowed real movements exhibited by PD patients are coupled with slower motor imagery and verb processing provides additional evidence for the involvement of the motor system in these processes. On the other hand, PD patients can still engage in motor imagery and action observation to some extent, which is encouraging for the use of these processes in rehabilitation. Findings across the different domains of action-representation reveal several important factors. First, the nature of action is critical: patients' performance in observation and naming tasks is influenced by whether or not the action is in their repertoire and by the extent of motion required to execute the action. Second, people with PD may use alternative or compensatory mechanisms to represent actions, such as relying more on a third-person perspective or a visual strategy. Third, people with PD show a lack of specificity, responding as strongly to stimuli related and unrelated to actions. Investigating action-representation in PD has implications for our understanding of both the symptoms of PD and the cognitive representation of actions in the healthy system.

Kids observing other kids' hands: visuomotor priming in children

We investigated motor resonance in children using a priming paradigm. Participants were asked to judge the weight of an object shortly primed by a hand in an action-related posture (grasp) or a non action-related one (fist). The hand prime could belong to a child or to an adult. We found faster response times when the object was preceded by a grasp hand posture (motor resonance effect). More crucially, participants were faster when the prime was a child's hand, suggesting that it could belong to their body schema, particularly when the child's hand was followed by a light object (motor simulation effect). A control experiment helped us to clarify the role of the hand prime. To our knowledge this is the first behavioral evidence of motor simulation and motor resonance in children. Implications of the results for the development of the sense of body ownership and for conceptual development are discussed.