Ada Kritikos

Placing actions in context: motor facilitation following observation of identical and non-identical manual acts.

It has been argued that through a process of internal ‘simulation’, we automatically map observed actions directly onto our motor system to facilitate imitation. Instead, here we show that observed actions influence the kinematic parameters of manual responses in a dynamic, context-dependent fashion. Participants observed object-directed hand actions in imitative and complementary action contexts, and performed identical (same grip-type) and non-identical (opposite grip-type) responses to a similar object, respectively. In imitative contexts, identical actions were performed optimally. In complementary contexts, however, non-identical actions were enhanced relative to identical actions. A further experiment using arrow cues instead of hand actions confirmed that these results were specific to action observation. Our findings demonstrate that action context plays a critical role in determining the relationship between action observation and execution. Crucially, this relationship is not fixed, but depends on an agent’s goal when observing others act.

Grasping the concept of personal property

The concept of property is integral to personal and societal development, yet understanding of the cognitive basis of ownership is limited. Objects are the most basic form of property, so our physical interactions with owned objects may elucidate nuanced aspects of ownership. We gave participants a coffee mug to decorate, use and keep. The experimenter also designed a mug of her own. In Experiment 1, participants performed natural lifting actions with each mug. Participants lifted the Experimenters mug with greater care, and moved it slightly more towards the Experimenter, while they lifted their own mug more forcefully and drew it closer to their own body. In Experiment 2, participants responded to stimuli presented on the mug handles in a computer-based stimulus-response compatibility task. Overall, participants were faster to respond in trials in which the handles were facing in the same direction as the response location compared to when the handles were facing away. The compatibility effect was abolished, however, for the Experimenters mug--as if the action system is blind to the potential for action towards another persons property. These findings demonstrate that knowledge of the ownership status of objects influences visuomotor processing in subtle and revealing ways.

Interference from Distractors in Reach-to-grasp Movements

Descriptions of interference effects from non-relevant stimuli are extensive in visual target detection and identification paradigms. To explore the influence of features of non-relevant objects on reach-to-grasp movements, we instructed healthy normal controls to reach for and pick up a cylinder (target) placed midsagittally 30 cm from the starting position of the hand. In Experiment 1, the target was presented alone, or accompanied by a narrower, wider, or same-size distractor positioned to the left or right of the target. In Experiment 2, the target was presented alone or accompanied by a distractor, which was slanted at a different orientation to the target. Reflective markers were placed on the wrist, thumb, and index finger of the right hand, and infra-red light-detecting cameras recorded their displacement through a calibrated 3-dimensional working space. Kinematic parameters were derived and analysed. Consistent changes in the expression of peak velocity, acceleration, and deceleration were evident when the distractor was narrower or wider than the target. The impact of the orientation of the distractor, conversely, was not marked. We discuss the results in the context of physiological findings and models of selective attention.

Human inferior parietal cortex 'programs' the action class of grasping

If one writes with a pen grasped between the toes, or a pencil held in the mouth, the handwriting style may be of poor quality but can be identified as belonging to a particular individual. Like other actions, such as grasping or pointing, different body parts can be used to produce the movement. These findings, of reasonably consistent spatial and temporal productions by different effectors, have been used to argue for the concept of motor equivalence and the existence of motor programs abstracted from particular effectors. In this study subjects were required to perform an action (grasping a sweet) with different effectors (the mouth or the hand) while the brain was scanned. Activation of the inferior parietal lobe during real and imagined mouth grasping, and during real hand grasping actions was demonstrated. Primate neurophysiological research has implicated this region in a movement-planning role. Our results confirm the importance of the inferior parietal lobe in integrating converging multimodal sensory information for coding of general action patterns in humans.

How frontoparietal brain regions mediate imitative and complementary actions: An FMRI study

The ‘mirror neuron system’ (MNS), located within inferior parietal lobe (IPL) and inferior frontal gyrus (IFG), creates an internal motor representation of the actions we see and has been implicated in imitation. Recently, the MNS has been implicated in non-identical responses: when the actions we must execute do not match those that we observe. However, in such conflicting situations non action-specific cognitive control networks also located in frontoparietal regions may be involved. In the present functional magnetic resonance imaging (fMRI) study participants made both similar and dissimilar actions within two action contexts: imitative and complementary. We aimed to determine whether activity within IPL/IFG depends on (i) responding under an imitative versus complementary context (ii) responding with similar versus dissimilar responses, and (iii) observing hand actions versus symbolic arrow cue stimuli. Activity within rIPL/rIFG regions was largest during observation of hand actions compared with arrow cues. Specifically, rIPL/rIFG were recruited only during the imitative context, when participants responded with similar actions. When responding to symbolic arrow cues, rIPL/rIFG activity increased during dissimilar responses, reflecting increased demands placed on general cognitive control mechanisms. These results suggest a specific role of rIPL/rIFG during imitation of hand actions, and also a general role of frontoparietal areas in mediating dissimilar responses to both hand actions and symbolic stimuli. We discuss our findings in relation to recent work that has examined the role of frontoparietal brain structures in joint-actions and inter-actor cooperation. We conclude that the specific brain regions identified here to show increased activation during action observation conditions are likely to form part of a mechanism specifically involved in matching observed actions directly with internal motor plans. Conversely, observation of arrow cues recruited part of a wider cognitive control network involved in the rapid remapping of stimulus-response associations.

Object ownership and action: The influence of social context and choice on the physical manipulation of personal property

Abstract Understanding who owns what is important for guiding appropriate action in a social context. Previously, we demonstrated that ownership influences our kinematic patterns associated with hand–object interactions (Constable et al. in Cognition 119(3):430–437, 2011). Here, we present a series of experiments aimed at determining the underlying mechanisms associated with this effect. We asked participants to lift mugs that differed in terms of ownership status (Experiments 1 and 2) and personal preference (Experiment 3) while recording spatial and acceleration measures. In Experiment 1, participants lifted their own mug with greater acceleration and drew it closer to themselves than they did the experimenter’s mug. They also lifted the experimenter’s mug further to the right compared with other mugs. In Experiment 2, spatial trajectory effects were preserved, but the acceleration effect abolished, when the owner of the ‘other-owned’ mug was a known—but absent—confederate. Experiment 3 demonstrated that merely choosing to use a mug was not sufficient to elicit rightward drift or acceleration effects. We suggest that these findings reflect separate and distinct mechanisms associated with socially related visuomotor processing.

Modulation of reach-to-grasp parameters: semantic category, volumetric properties and distractor interference?

Abstract. In the two experiments of this study, we assessed the influence of target size and semantic category on the expression of reach-to-grasp kinematic parameters. Moreover, we investigated the influence of size and semantic category of distractors on reaches to the target. The experimental objects represented living and non-living categories and wide and narrow grasp sizes. Participants reached for and picked up mid-sagittally placed targets, which were either alone or flanked by distractors congruent or incongruent to semantic category and size of the target. In experiment 1, movement duration was faster to living objects. We could not replicate this, however, in experiment 2. Conversely, significant and reliable Category × Size interactions for grasp were obtained in experiment 1 and replicated in experiment 2. The pattern of the means in these interactions coincided with the absolute volumetric properties of the stimuli, indicating that the size of the stimuli was the main determinant of the expression of kinematic parameters. We conclude that volumetric properties such as size, rather than semantic category, are the crucial features in the programming and execution of movement to targets. As regards the category and size of the distractor, interference effects were evident: both category and size exerted a comparable influence on reaches to the target. The direction of interference, however, was not systematic. The interference effects are discussed in the context of visual search models of attention.

Mountain high, valley low: direction-specific effects of articulation on reaching.

Representations underpinning action and language overlap and interact very closely. There are bidirectional interactions between word and action comprehension, semantic processing of language, and response selection. This study extends our understanding of the influence of speech on concurrent motor execution. Participants reached-to-grasp the top or bottom of a vertically oriented bar in response to the location of a word on a computer screen (top/bottom). Words were synonyms for “up” or “down”, and participants were required to articulate the word during movement. We were particularly interested in the influence of articulated word semantics on the transport component of the reach. Using motion capture to analyse action kinematics, we show that irrespective of reach direction, saying “up” synonyms led to greater height of the hand, while saying “down” synonyms was associated with reduced height. This direction-specific influence of articulation on the spatial parameters of the hand supports the idea that linguistic systems are tightly integrated and influence each other.

Tactile interference in visually guided reach-to-grasp movements

This study addresses the issue of cross-modal links in goal-directed actions and specifically the influence of non-relevant tactile information on visually guided reach-to-grasp movements. Right-handed participants reached for and grasped with either their left or right hand a visually presented, midsagitally placed target. The target was presented alone, or was accompanied by an unseen, tactile distractor placed in the non-reaching hand. The tactile distractor was either smaller than, the same size as or larger than the target. Significant alterations in kinematic parameterisation were restricted to the grasp component of the movement, and specifically to the reaching right hand. More importantly, the size of the unseen tactile distractors in the left hand altered the grasp parameterisation of the right hand. These findings are discussed in the context of current theories of the control of action by perceptual processes.

Pictures of disgusting foods and disgusted facial expressions suppress the tongue motor cortex

Abstract The tongue holds a unique role in gustatory disgust. However, it is unclear whether the tongue representation in the motor cortex (tM1) is affected by the sight of distaste-related stimuli. Using transcranial magnetic stimulation (TMS) in healthy humans, we recorded tongue motor-evoked potentials (MEPs) as an index of tM1 cortico-hypoglossal excitability. MEPs were recorded while participants viewed pictures associated with gustatory disgust and revulsion (i.e. rotten foods and faces expressing distaste), non-oral-related disgusting stimuli (i.e. invertebrates like worms) and control stimuli. We found that oral-related disgust pictures suppressed tM1 cortico-hypoglossal output. This tM1 suppression was predicted by interindividual differences in disgust sensitivity. No similar suppression was found for disgusting invertebrates or when MEPs were recorded from a control muscle. These findings suggest that revulsion-eliciting food pictures trigger anticipatory inhibition mechanisms, possibly preventing toxin swallowing and contamination. A similar suppression is elicited when viewing distaste expressions, suggesting vicarious motor inhibition during social perception of disgust. Our study suggests an avoidant-defensive mechanism in human cortico-hypoglossal circuits and its ‘resonant’ activation in the vicarious experience of others’ distaste. These findings support a role for the motor system in emotion-driven motor anticipation and social cognition.