Predictability shapes movement kinematics and grip force regulation in human object handovers.

In contrast to a self-generated action, a human-to-human object handover represents a semi-predictable task, due to a lack of exact knowledge about the partner's future movement behavior. Thus far, it has not been determined which behavioral characteristics result from dealing with this prevailing uncertainty, although this distinction would enhance the understanding of underlying motor control strategies in such semi-predictable situations. Behavioral effects of mutual interaction during object handovers were therefore investigated in the current study, by comparing grip force profiles and kinematic data from predictable solo-handovers (between the two hands of one person) with data from semi-predictable partner-handovers. There were significant decreases in passers' mean release rates as well as corresponding increases in handover durations in partner-handovers compared to solo-handovers. Likewise, receivers in partner-handovers employed lower mean grip force rates to take the object, which speaks for feedback reliance of both partners in the load transfer process of partner-handovers. Increased vertical object displacement in this phase might represent timing deficits due to the prediction uncertainties in partner-handovers. The data also provided first evidence that left-handed people serving as receivers in partner-handovers exhibit an altered take-over strategy compared to right-handed receivers.

Relevance of Predictive and Postdictive Error Information in the Course of Motor Learning.

The prediction of the sensory consequences of physical movements is a fundamental feature of the human brain. This function is attributed to a forward model, which generates predictions based on sensory and efferent information. The neural processes underlying such predictions have been studied using the error-related negativity (ERN) as a fronto-central event-related potential in electroencephalogram (EEG) tracings. In this experiment, 16 participants practiced a novel motor task for 4000 trials over ten sessions. Neural correlates of error processing were recorded in sessions one, five, and ten. Along with significant improvements in task performance, the ERN amplitude increased over the sessions. Simultaneously, the feedback-related negativity (FRN), a neural marker corresponding to the processing of movement-outcome feedback, attenuated with learning. The findings suggest that early in learning, the motor control system relies more on information from external feedback about terminal outcome. With increasing task performance, the forward model is able to generate more accurate outcome predictions, which, as a result, increasingly contributes to error processing. The data also suggests a complementary relationship between the ERN and the FRN over motor learning.

Focused Review on Neural Correlates of Different Types of Motor Errors and Related Terminological Issues.

The Error-related negativity (Ne/ERN) and the feedback-related negativity (FRN), two event-related potentials in electroencephalogram tracings, have been used to examine error processing in conscious actions. In the classical terminology the Ne/ERN and the FRN are differentiated with respect to whether internal (Ne/ERN) or external (FRN) error information is processed. In motor tasks, however, errors of different types can be made: A wrong action can be selected that is not adequate to achieve the task goal (or action effect), or the correctly selected action can be mis-performed such that the task goal might be missed (movement error). Depending on the motor task and the temporal sequences of these events, internal and external error information can coincide. Hence, a clear distinction of the information source is difficult, and the classical terminology that differentiates the Ne/ERN and the FRN with respect to internal and external error information becomes ambiguous. But, a stronger focus on the characteristics of the definition of "task" and the cause of "errors", as well as on temporal characteristics of event-related potentials with respect to the task action allows separate examination of the processing of movement errors, the processing of the prediction of action effect errors, or the processing of the detection of action effect errors. The present article gives an overview of example studies investigating the Ne/ERN and the FRN in motor tasks, classifies them with respect to action effect errors or movement errors, and proposes updated terminology.

Grip-force modulation in human-to-human object handovers: effects of sensory and kinematic manipulations.

From a motor control perspective, human-to-human object handovers can be described as coordinated joint-actions transferring the power over an object from a passer to a receiver. Although, human-to-human handovers are very reliable in terms of success, it is unclear how both actors plan and execute their actions independently while taking into account the partners behaviour. Here, we measured grip-forces of passer and receiver while handing over an object. In order to study mutual interaction in human-to-human handovers, we measured how changes in relevant features (sensory information available to the passer and receiver's reaching velocity) in one partner affect grip-force profiles not only at the manipulated side but also at the partner's side. The data reveals strong effects of sensory manipulations on time-related (duration and release delay) and dynamometric measures (force rates). Variation of reaching velocities had the largest impact on the receiver's force rates. Furthermore, there are first indications that the vertical object movement is used as an implicit cue to signal the start of the handover in situations where vision is restricted.

Predictive error processing distinguishes between relevant and irrelevant errors after visuomotor learning.

Error processing is an important aspect of learning. The detection and online correction of an error as well as error-based adaptation of subsequent movements enables humans to improve behavior. For this improvement, it is necessary to differentiate between relevant and irrelevant errors. Behavioral adaptations are only reasonable when an error is attributed to one's own behavior and therefore regarded as relevant for subsequent adjustments, whereas irrelevant errors caused by unsystematic external influences should be disregarded. Here, we ask whether error predictions as indexed by the error-related negativity (Ne/ERN) can be used to differentiate relevant and irrelevant errors in movements with a complex visuomotor mapping. Using event-related potentials, we compared the neural activation between relevant (self-induced/internal) errors and irrelevant (externally manipulated) errors in a virtual goal-oriented throwing task. Results show that the Ne/ERN responds more strongly to self-induced errors, while the feedback-related negativity (FRN) more strongly correlates with externally manipulated errors. Moreover, subsequent behavioral adjustments were larger in the relevant compared to the irrelevant error trials. We conclude that predictive processes, marked by the Ne/ERN, can subserve error attribution in naturalistic, complex visuomotor tasks like throwing.

Inference statistical analysis of continuous data based on confidence bands-Traditional and new approaches.

In the analysis of continuous data, researchers are often faced with the problem that statistical methods developed for single-point data (e.g., t test, analysis of variance) are not always appropriate for their purposes. Either methodological adaptations of single-point methods will need to be made, or confidence bands are the method of choice. In this article, we compare three prominent techniques to analyze continuous data (single-point methods, Gaussian confidence bands, and function-based resampling methods to construct confidence bands) with regard to their testing principles, prerequisites, and outputs in the analysis of continuous data. In addition, we introduce a new technique that combines the advantages of the existing methods and can be applied to a wide range of data. Furthermore, we introduce a method enabling a priori and a posteriori power analyses for experiments with continuous data.

Specificity of Postural Control: Comparing Expert and Intermediate Dancers.

The expert-novice approach is inappropriate for studying postural control in sport and dance when novices are completely unable to perform relevant postural tasks and experts cannot demonstrate specific skills on everyday postural tasks. We tested expertise-specific differences on 6 static everyday and 5 dynamic dance-like postural tasks of varying difficulty in 13 professional and 12 intermediate nonprofessional dancers. Results showed a clear expert advantage on sway area for dance-like postural tasks, but not for static everyday tasks. This effect was also found for the control parameter of root mean square (RMS) velocity and partly for RMS amplitude of the difference signal between CoP and CoG line location. Results indicate that the expert advantage is task-specific and deliver new insights into the specificity of experts' postural performance.

Accuracy of Motor Error Predictions for Different Sensory Signals.

Detecting and evaluating errors in action execution is essential for learning. Through complex interactions of the inverse and the forward model, the human motor system can predict and subsequently adjust ongoing or subsequent actions. Inputs to such a prediction are efferent and afferent signals from various sources. The aim of the current study was to examine the impact of visual as well as a combination of efferent and proprioceptive input signals to error prediction in a complex motor task. Predicting motor errors has been shown to be correlated with a neural signal known as the error-related negativity (Ne/ERN). Here, we tested how the Ne/ERN amplitude was modulated by the availability of different sensory signals in a semi-virtual throwing task where the action outcome (hit or miss of the target) was temporally delayed relative to movement execution allowing participants to form predictions about the outcome prior to the availability of knowledge of results. 19 participants practiced the task and electroencephalogram was recorded in two test conditions. In the Visual condition, participants received only visual input by passively observing the throwing movement. In the EffProp condition, participants actively executed the task while visual information about the real and the virtual effector was occluded. Hence, only efferent and proprioceptive signals were available. Results show a significant modulation of the Ne/ERN in the Visual condition while no effect could be observed in the EffProp condition. In addition, amplitudes of the feedback-related negativity in response to the actual outcome feedback were found to be inversely related to the Ne/ERN amplitudes. Our findings indicate that error prediction is modulated by the availability of input signals to the forward model. The observed amplitudes were found to be attenuated in comparison to previous studies, in which all efferent and sensory inputs were present. Furthermore, we assume that visual signals are weighted higher than proprioceptive signals, at least in goal-oriented tasks with visual targets.

Brain negativity as an indicator of predictive error processing: the contribution of visual action effect monitoring.

The error (related) negativity (Ne/ERN) is an event-related potential in the electroencephalogram (EEG) correlating with error processing. Its conditions of appearance before terminal external error information suggest that the Ne/ERN is indicative of predictive processes in the evaluation of errors. The aim of the present study was to specifically examine the Ne/ERN in a complex motor task and to particularly rule out other explaining sources of the Ne/ERN aside from error prediction processes. To this end, we focused on the dependency of the Ne/ERN on visual monitoring about the action outcome after movement termination but before result feedback (action effect monitoring). Participants performed a semi-virtual throwing task by using a manipulandum to throw a virtual ball displayed on a computer screen to hit a target object. Visual feedback about the ball flying to the target was masked to prevent action effect monitoring. Participants received a static feedback about the action outcome (850 ms) after each trial. We found a significant negative deflection in the average EEG curves of the error trials peaking at ~250 ms after ball release, i.e., before error feedback. Furthermore, this Ne/ERN signal did not depend on visual ball-flight monitoring after release. We conclude that the Ne/ERN has the potential to indicate error prediction in motor tasks and that it exists even in the absence of action effect monitoring.NEW & NOTEWORTHY In this study, we are separating different kinds of possible contributors to an electroencephalogram (EEG) error correlate (Ne/ERN) in a throwing task. We tested the influence of action effect monitoring on the Ne/ERN amplitude in the EEG. We used a task that allows us to restrict movement correction and action effect monitoring and to control the onset of result feedback. We ascribe the Ne/ERN to predictive error processing where a conscious feeling of failure is not a prerequisite.

No transfer between conditions in balance training regimes relying on tasks with different postural demands: Specificity effects of two different serious games.

Despite the increasing use of video games involving whole body movements to enhance postural control in health prevention and rehabilitation, there is no consistent proof that training effects actually transfer to other balance tasks. The present study aimed to determine whether training effects on two different video-game-based training devices were task-specific or could be transferred to either postural control in quiet stance or to performance on the other device. 37 young healthy adults were split into three groups: two intervention groups that trained for 30min on either the Nintendo(®) Wii Fit Balance Board or the MFT Challenge Disc(®) three times per week for 4 weeks and a control group that received no training. All games require participants to control virtual avatars by shifting the center of mass in different directions. Both devices differ in their physical properties. The Balance Board provides a stable surface, whereas the Challenge Disc can be tilted in all directions. Dependent variables were the game scores on both devices and the center of pressure (COP) displacements measured via force plate. At posttest, both intervention groups showed significant increases in performance on the trained games compared to controls. However, there were no relevant transfer effects to performance on the untrained device and no changes in COP path length in quiet stance. These results suggest that training effects on both devices are highly specific and do not transfer to tasks with different postural demands.