Kinematics fingerprints of leader and follower role-taking during cooperative joint actions

n/

Brain Dynamics of Action Monitoring in Higher-Order Motor Control Disorders: The Case of Apraxia

Limb apraxia (LA) refers to a high-order motor disorder characterized by the inability to reproduce transitive actions on commands or after observation. Studies demonstrate that action observation and action execution activate the same networks in the human brain, and provides an onlooker’s motor system with appropriate cognitive, motor and sensory-motor cues to flexibly implementing action-sequences and gestures. Tellingly, the temporal dynamics of action monitoring has never been explored in people suffering from LA. To fill this gap, we studied the electro-cortical signatures of error observation in human participants suffering from acquired left-brain lesions with (LA+) and without (LA–) LA, and in a group of healthy controls (H). EEG was acquired while participants observed from a first-person perspective (1PP) an avatar performing correct or incorrect reach-to-grasp a glass action in an immersive-virtual environment. Alterations of typical EEG signatures of error observation in time (early error positivity; Pe) and time-frequency domain (theta band-power) were found reduced in LA+ compared with H. Connectivity analyses showed that LA+ exhibited a decreased theta phase synchronization of both the frontoparietal and frontofrontal network, compared with H and LA–. Moreover, linear regression analysis revealed that the severity of LA [test of upper LA (TULIA) scores] was predicted by mid-frontal error-related theta activity, suggesting a link between error monitoring capacity and apraxic phenotypes. These results provide novel neurophysiological evidence of altered neurophysiological dynamics of action monitoring in individuals with LA and shed light on the performance monitoring changes occurring in this disorder

Long-latency modulation of motor cortex excitability by ipsilateral posterior inferior frontal gyrus and pre-supplementary motor area

The primary motor cortex (M1) is strongly influenced by several frontal regions. Dual-site transcranial magnetic stimulation (dsTMS) has highlighted the timing of early (<40 ms) prefrontal/premotor influences over M1. Here we used dsTMS to investigate, for the first time, longer-latency causal interactions of the posterior inferior frontal gyrus (pIFG) and pre-supplementary motor area (pre-SMA) with M1 at rest. A suprathreshold test stimulus (TS) was applied over M1 producing a motor-evoked potential (MEP) in the relaxed hand. Either a subthreshold or a suprathreshold conditioning stimulus (CS) was administered over ipsilateral pIFG/pre-SMA sites before the TS at different CS-TS inter-stimulus intervals (ISIs: 40-150 ms). Independently of intensity, CS over pIFG and pre-SMA (but not over a control site) inhibited MEPs at an ISI of 40 ms. The CS over pIFG produced a second peak of inhibition at an ISI of 150 ms. Additionally, facilitatory modulations were found at an ISI of 60 ms, with supra-but not subthreshold CS intensities. These findings suggest differential modulatory roles of pIFG and pre-SMA in M1 excitability. In particular, the pIFG-but not the pre-SMA-exerts intensity-dependent modulatory influences over M1 within the explored time window of 40-150 ms, evidencing fine-tuned control of M1 output

Reliability and Feasibility of Linear Mixed Models in Fully Crossed Experimental Designs

The use of linear mixed models (LMMs) is increasing in psychology and neuroscience research In this article, we focus on the implementation of LMMs in fully crossed experimental designs. A key aspect of LMMs is choosing a random-effects structure according to the experimental needs. To date, opposite suggestions are present in the literature, spanning from keeping all random effects (maximal models), which produces several singularity and convergence issues, to removing random effects until the best fit is found, with the risk of inflating Type I error (reduced models). However, defining the random structure to fit a nonsingular and convergent model is not straightforward. Moreover, the lack of a standard approach may lead the researcher to make decisions that potentially inflate Type I errors. After reviewing LMMs, we introduce a step-by-step approach to avoid convergence and singularity issues and control for Type I error inflation during model reduction of fully crossed experimental designs. Specifically, we propose the use of complex random intercepts (CRIs) when maximal models are overparametrized. CRIs are multiple random intercepts that represent the residual variance of categorical fixed effects within a given grouping factor. We validated CRIs and the proposed procedure by extensive simulations and a real-case application. We demonstrate that CRIs can produce reliable results and require less computational resources. Moreover, we outline a few criteria and recommendations on how and when scholars should reduce overparametrized models. Overall, the proposed procedure provides clear solutions to avoid overinflated results using LMMs in psychology and neuroscience

EEG indices of performance monitoring activity and error predictability: embodying the actions of an avatar in immersive virtual reality

Electro-cortical signatures of performance errors are thought to indicate the need for top-down control. Mid-frontal Theta oscillatory activity (4-8Hz) is a well-established marker of committed or observed errors. By combining EEG and immersive virtual reality, we reported that observing errors in reach-to-grasp actions of an avatar seen from a first-person perspective elicited greater theta oscillations over fronto-central electrodes (Pavone et al., 2016). Previous studies on committed or observed errors used sequences of trials were erroneous actions were less frequent than correct actions (e.g. 30% vs 70%). Therefore, it was not possible to disentangle whether the activation of the performance system was due to error per se or to surprise/novelty effect associated with rare and less predictable events. To address this issue, we recorded the EEG signal of 20 participants observing correct or erroneous actions performed by an avatar. Importantly, at variance with Pavone et al, (2016) the proportion of erroneous vs correct actions was 70% vs 30%. The results show that observation of erroneous actions enhanced Theta power compared to correct actions. Our data suggest that error per se, and not its percentage of occurrence, triggered the activity of the performance monitoring system, likely with the aim of flexibly adapting actions to the challenges of the external environment

Re-establishing the disrupted sensorimotor loop in deafferented and deefferented people: The case of spinal cord injuries

Acting efficiently in the world depends on the activity of motor and somatosensory systems, the integration of which is necessary for the proper functioning of the sensorimotor loop (SL). Profound alterations of SL functioning follow spinal cord injury (SCI), a condition that brings about a disconnection of the body from the brain. Such disconnection creates a substantial deprivation of somatosensorial inputs and motor outputs. Consequent somatic deficits and motor paralysis affect the body below the lesion level. A complete restoration of normal functions of the SL cannot be expected until basic neuroscience has found a way to re-establish the interrupted neural connectivity. Meanwhile, studies should focus on the development of technical solutions for dealing with the disruption of the sensorimotor loop. This review discusses the structural and functional adaptive reorganization of the brain after SCI, and the maladaptive mechanisms that impact on the processing of body related information, which alter motor imagery strategies and EEG signals. Studies that show how residual functions (e.g. face tactile sensitivity) may help people to restore a normal body image are also reviewed. Finally, data on how brain and residual body signals may be used to improve brain computer interface systems is discussed in relation to the issue of how such systems may help SCI people to re-enter the world and interact with objects and other individuals

Mere observation of body discontinuity affects perceived ownership and vicarious agency over a virtual hand

The mental representation of one’s body typically implies the continuity of its parts. Here, we used immersive virtual reality to explore whether mere observation of visual discontinuity between the hand and limb of an avatar could influence a person’s sense of ownership of the virtual body (feeling of ownership, FO) and being the agent of its actions (vicarious agency, VA). In experiment 1, we tested whether placing different amounts of visual discontinuity between a virtual hand and limb differently modulate the perceived FO and VA. Participants passively observed from a first-person perspective four different versions of a virtual limb: (1) a full limb; a hand detached from the proximal part of the limb because of deletion of (2) the wrist; (3) the wrist and forearm; (4) and the wrist, forearm and elbow. After observing the static or moving virtual limb, participants reported their feeling of ownership (FO) and vicarious agency (VA) over the hand. We found that even a small visual discontinuity between the virtual hand and arm significantly decreased participants’ FO over the hand during observation of the static limb. Moreover, in the same condition, we found that passive observation of the avatar’s actions induced a decrease in both FO and VA. We replicated the same results in a second study (experiment 2) where we investigated the modulation of FO and VA by comparing the visual body discontinuity with a condition in which the virtual limb was partially occluded. Our data show that mere observation of limb discontinuity can change a person’s ownership and agency over a virtual body observed from a first-person perspective, even in the absence of any multisensory stimulation of the real body. These results shed new light on the role of body visual continuity in modulating self-awareness and agency in immersive virtual reality

Body Form Modulates the Prediction of Human and Artificial Behaviour from Gaze Observation

The future of human-robot collaboration relies on people's ability to understand and predict robots' actions. The machine-like appearance of robots, as well as contextual information, may influence people's ability to anticipate the behaviour of robots. We conducted six separate experiments to investigate how spatial cues and task instructions modulate people's ability to understand what a robot is doing. Participants observed goal-directed and non-goal directed gaze shifts made by human and robot agents, as well as directional cues displayed by a triangle. We report that biasing an observer's attention, by showing just one object an agent can interact with, can improve people's ability to understand what humanoid robots will do. Crucially, this cue had no impact on people's ability to predict the upcoming behaviour of the triangle. Moreover, task instructions that focus on the visual and motor consequences of the observed gaze were found to influence mentalising abilities. We suggest that the human-like shape of an agent and its physical capabilities facilitate the prediction of an upcoming action. The reported findings expand current models of gaze perception and may have important implications for human-human and human-robot collaboration

Action simulation plays a critical role in deceptive action recognition

The ability to infer deception from nonverbal behavior is critical for social interactions. By combining single-pulse and repetitive transcranial magnetic stimulation (TMS), we provide correlational and causative evidence that action simulation is actively involved in the ability to detect deceptive behavior. We recorded motor-evoked potentials during a faked-action discrimination (FAD) task: participants watched videos of actors lifting a cube and judged whether the actors were trying to deceive them concerning the real weight of the cube. Seeing deceptive actions facilitated the observers\u2019 motor system more than truthful actions, suggesting that motor resonance was sensitive to perceived deceits. Furthermore, we found that TMS disruption of inferior frontal cortex (IFC) but not of temporo-parietal junction (TPJ, control site) reduced perceptual sensitivity in the FAD-task. These findings indicate that IFC is necessary for inferring deceits from observed actions and suggest that FAD relies on the simulation of subtle changes in action kinematics