Perceived cognitive fatigue has only marginal effects on static balance control in healthy young adults.

We examined the influence of perceived cognitive fatigue on static balance control in healthy young adults to gain greater clarity about this issue than provided in previous research. Based on the prevailing assumption in pertinent literature, we hypothesized that the influence of cognitive fatigue on balance control depends on the attentional effort required by the balance tasks being performed. To test this hypothesis, 44 young adults (24 women and 20 men) were alternately assigned to either the experimental group that was cognitively fatigued (using the 16-min TloadDback-task with individualized settings) or the control group (who watched a documentary). Before and after the intervention, the participants performed six balance tasks that differed in (attentional) control requirements, while recording the center of pressure (COP). From these time series, sway variability, mean speed, and sample entropy were calculated and analyzed statistically. Additionally, perceived cognitive fatigue was assessed using VAS scales. Statistical analyses confirmed that the balance tasks differed in control characteristics and that cognitive fatigue was elevated in the experimental group, but not in the control group. Nevertheless, no significant main effects of cognitive fatigue were found on any of the COP measures of interest, except for some non-robust interaction effects related primarily to sample entropy. These results suggest that, in young adults, postural control in static balance tasks is largely automatic and unaffected by task-induced state fatigue.

Being (un)moved by mental time travel.

Mental imagery of events in the past or future, and of unpleasant or pleasant events, has been found to lead to spontaneous backward/forward bodily motions. Both time and emotion are represented along a spatial continuum, and activation of these representations seems to be simulated in spontaneous changes in body posture. We performed a conceptual replication and extension of an earlier study by Miles, Nind, and Macrae (2010) who reported clear postural effects when thinking of the past and the future. We additionally tested whether changes in posture appear when thinking of an emotional event. Volunteers engaged in mental imagery, involving combinations of time intervals and emotions. We simultaneously recorded center-of-pressure (COP) changes. Results revealed neither an effect of imagery of time nor of emotion on body posture. We conclude that embodied effects of imagery of abstract items on body posture may be less robust than suggested by previous literature.

Size estimates of action-relevant space remain invariant in the face of systematic changes to postural stability and arousal.

Perceptual estimates of action-relevant space have been reported to vary dependent on postural stability and concomitant changes in arousal. These findings contribute to current theories proposing that perception may be embodied. However, systematic manipulations to postural stability have not been tested, and a causal relationship between postural stability and perceptual estimates remains to be proven. We manipulated postural stability by asking participants to stand in three differently stable postures on a force plate measuring postural sway. Participants looked at and imagined traversing wooden beams of different widths and then provided perceptual estimates of the beams' widths. They also rated their level of arousal. Manipulation checks revealed that the different postures resulted in systematic differences in body sway. This systematic variation in postural stability was accompanied by significant differences in self-reported arousal. Yet, despite systematic differences in postural stability and levels of arousal perceptual estimates of the beams' widths remained invariant.

Social embodiment in directional stepping behavior.

Embodiment theories emphasize the role played by sensory and motor processes in psychological states, such as social information processing. Motivated by this idea, we examined how whole-body postural behaviors couple to social affective cues, viz., pictures of smiling and angry faces. We adopted a Simon-like paradigm, whereby healthy female volunteers were asked to select and initiate a forward or backward step on a force plate in response to the gender of the poser (male/female), regardless of emotion. Detailed analysis of the spatiotemporal unfolding of the body center of pressure during the steps revealed that task-irrelevant emotion had no effect on the initiation times of the steps, i.e., there was no evidence of an affective Simon effect. An unexpected finding was that steps were initiated relatively slow in response to female angry faces. This Stroop-like effect suggests that postural behavior is influenced by whether certain stimulus features match or mismatch.

Gait-modifying effects of augmented-reality cueing in people with Parkinson's disease.

Introduction: External cueing can improve gait in people with Parkinson's disease (PD), but there is a need for wearable, personalized and flexible cueing techniques that can exploit the power of action-relevant visual cues. Augmented Reality (AR) involving headsets or glasses represents a promising technology in those regards. This study examines the gait-modifying effects of real-world and AR cueing in people with PD. Methods: 21 people with PD performed walking tasks augmented with either real-world or AR cues, imposing changes in gait speed, step length, crossing step length, and step height. Two different AR headsets, differing in AR field of view (AR-FOV) size, were used to evaluate potential AR-FOV-size effects on the gait-modifying effects of AR cues as well as on the head orientation required for interacting with them. Results: Participants modified their gait speed, step length, and crossing step length significantly to changes in both real-world and AR cues, with step lengths also being statistically equivalent to those imposed. Due to technical issues, step-height modulation could not be analyzed. AR-FOV size had no significant effect on gait modifications, although small differences in head orientation were observed when interacting with nearby objects between AR headsets. Conclusion: People with PD can modify their gait to AR cues as effectively as to real-world cues with state-of-the-art AR headsets, for which AR-FOV size is no longer a limiting factor. Future studies are warranted to explore the merit of a library of cue modalities and individually-tailored AR cueing for facilitating gait in real-world environments.

Cinerama sickness and postural instability.

Motion sickness symptoms and increased postural instability induced by motion pictures have been reported in a laboratory, but not in a real cinema. We, therefore, carried out an observational study recording sickness severity and postural instability in 19 subjects before, immediately and 45 min after watching a 1 h 3D aviation documentary in a cinema. Sickness was significantly larger right after the movie than before, and in a lesser extent still so after 45 min. The average standard deviation of the lateral centre of pressure excursions was significantly larger only right afterwards. When low-pass filtered at 0.1 Hz, lateral and for-aft excursions were both significantly larger right after the movie, while for-aft excursions then remained larger even after 45 min. Speculating on previous findings, we predict more sickness and postural instability in 3D than in 2D movies, also suggesting a possible, but yet unknown risk for work-related activities and vehicle operation. PRACTITIONER SUMMARY: Watching motion pictures may be sickening and posturally destabilising, but effects in a cinema are unknown. We, therefore, carried out an observational study showing that sickness then is mainly an issue during the exposure while postural instability is an issue afterwards.

Task-relevant social cues affect whole-body approach-avoidance behavior.

Positively evaluated stimuli facilitate approach and negatively evaluated stimuli prompt avoidance responses, as typically measured by reaction time differences when moving a joystick toward the own body or away from it. In this study, we explore whether a whole-body response (forward and backward leaning can serve as a better indicator of approach-avoidance behavior; AA). Thirty-two subjects were presented with pictures of males and females with angry or happy facial expressions. Subjects had to perform approach or avoidance responses by leaning forward or backward, either based on the facial expression of the stimulus or the gender of the stimulus. Leaning responses were sensitive to angry faces for explicit decision cues. Here, angry facial expressions facilitated backward leaning but not when responding to the gender of the stimulus. We compare this to the established manual measure of AA and discuss our results with regard to response coding.

A critical evaluation of the cognitive penetrability of posture.

UNLABELLED: BACKGROUND/STUDY CONTEXT: Interactions between postural control and cognitive activity as evidenced by dual-tasking studies are common, and especially pronounced in the elderly. Some authors have used this finding to suggest that posture is "cognitively penetrable." METHODS: The authors present a critical look at the "cognitive penetrability of posture" concept. The authors first trace the notion back to Pylyshyn ( 1980 , Behavioral and Brain Sciences, 3, 111-169) in the context of visual information processing. RESULTS: The authors then argue that dual-tasking interference effects do not prove that posture is penetrable by cognition. CONCLUSION: The authors conclude that it may be valid to study cognitive penetrability of posture, but that such an endeavor is served best by adopting a hierarchical model of action control.

Walk to me when I smile, step back when I'm angry: emotional faces modulate whole-body approach-avoidance behaviors.

Facial expressions are potent social cues that can induce behavioral dispositions, such as approach-avoidance tendencies. We studied these tendencies by asking participants to make whole-body forward (approach) or backward (avoidance) steps on a force plate in response to the valence of social cues (happy or angry faces) under affect-congruent and incongruent mappings. Posturographic parameters of the steps related to automatic stimulus evaluation, step initiation (reaction time), and step execution were determined and analyzed as a function of stimulus valence and stimulus-response mapping. The main result was that participants needed more time to initiate a forward step towards an angry face than towards a smiling face (which is evidence of a congruency effect), but with backward steps, this difference failed to reach significance. We also found a reduction in spontaneous body sway prior to the step with the incongruent mapping. The results provide a crucial empirical link between theories of socially induced action tendencies and theories of postural control and suggest a motoric basis for socially guided motivated behavior.

Theta-burst transcranial magnetic stimulation for the treatment of unilateral neglect in stroke patients: A systematic review and best evidence synthesis.

BACKGROUND: Unilateral neglect (UN) is a common and disabling disorder after stroke. UN is a strong and negative predictor of functional rehabilitative outcome. Non-invasive brain stimulation, such as theta-burst transcranial magnetic stimulation (TBS), is a promising rehabilitation technique for treating stroke-induced UN. OBJECTIVE: To systematically review the available literature, researching whether TBS of the contra-lesional hemisphere is more effective than standard rehabilitation in improving symptoms of UN in patients with right hemisphere stroke. REVIEW METHODS: A systematic review was conducted to retrieve randomized controlled trials (RCTs) that were relevant to the objective of this review. PubMed, Ovid and Cochrane Library electronic databases were comprehensively searched from inception up to February 2021. Of the included studies, methodological quality was assessed using the PEDro scale, whereafter a best evidence synthesis (BES) was conducted to summarize the results. RESULTS: Nine RCTs investigating the effects of TBS on stroke-induced UN symptoms were included in this review. Seven studies assessing continuous TBS (cTBS) found significantly greater amelioration of UN symptoms in the TBS intervention group when compared to the control group; one study assessing cTBS found no such significant difference. One study assessing intermittent TBS (iTBS) found significant between-group differences in favor of the intervention. The BES yielded strong evidence in favor of cTBS, and limited evidence in favor of iTBS. CONCLUSIONS: The included studies in the present review allow the conclusion that TBS can have favorable effects on UN recovery in stroke patients. Its clinical use is recommended in conjunction with cognitive rehabilitation and occupational or physical rehabilitation as needed. However, many aspects for optimal usage of TBS therapy in clinical settings, such as exact TBS protocols, number of sessions, and treatment duration, are not clear.

On the physiology of interruption after unexpectedness.

We tested whether surprise elicits similar physiological changes as those associated with orienting and freezing after threat, as surprise also involves a state of interruption and attention for effective action. Moreover, because surprise is primarily driven by the unexpectedness of an event, initial physiological responses were predicted to be similar for positive, neutral, and negative surprises. Results of repetition-change studies (4 + 1 in Supplemental Materials) showed that surprise lowers heart rate (Experiments 1-4) and increases blood pressure (Experiment 4). No effects on body movement (Experiment 2) or finger temperature (Experiment 4) were found. When unexpected stimuli were presented more often (making them less surprising) heart rate returned to baseline, while blood pressure remained high (Experiment 4). These effects were not influenced by stimulus valence. However, second-to-second analyses within the first (surprising) block showed a tendency for a stronger increase in systolic blood pressure after negative vs. positive surprise.

Facing freeze: social threat induces bodily freeze in humans.

Freezing is a common defensive response in animals threatened by predators. It is characterized by reduced body motion and decreased heart rate (bradycardia). However, despite the relevance of animal defense models in human stress research, studies have not shown whether social threat cues elicit similar freeze-like responses in humans. We investigated body sway and heart rate in 50 female participants while they were standing on a stabilometric force platform and viewing cues that were socially threatening, socially neutral, and socially affiliative (angry, neutral, and happy faces, respectively). Posturographic analyses showed that angry faces (compared with neutral faces and happy faces) induced significant reductions in body sway. In addition, the reduced body sway for angry faces was accompanied by bradycardia and correlated significantly with subjective anxiety. Together, these findings indicate that spontaneous body responses to social threat cues involve freeze-like behavior in humans that mimics animal freeze responses. These findings open avenues for studying human freeze responses in relation to various sociobiological markers and social-affective disorders.

Patterns of postural sway in high anxious children.

BACKGROUND: Current research suggests that elevated levels of anxiety have a negative impact on the regulation of balance. However, most studies to date examined only global balance performance, with little attention to the way body posture is organized in space and time. The aim of this study is to examine whether posturographic measures can reveal (sub)clinical balance deficits in children with high levels of anxiety. METHODS: We examined the spatio-temporal structure of the centre-of-pressure (COP) fluctuations in children with elevated levels of anxiety and a group of typically developing children while maintaining quiet stance on a force plate in various balance challenging conditions. Balance was challenged by adopting sensory manipulations (standing with eyes closed and/or standing on a foam surface) and using a cognitive manipulation (dual-tasking). RESULTS: Across groups, postural performance was strongly influenced by the sensory manipulations, and hardly by the cognitive manipulation. We also found that children with anxiety had overall more postural sway, and that their postural sway was overall less complex than sway of typically developing children. The postural differences between groups were present even in the simple baseline condition, and the group differences became larger with increasing task difficulty. CONCLUSION: The pattern of postural sway suggests that balance is overall less stable and more attention demanding in children with anxiety than typically developing children. The findings provide further evidence for a neuro-behavioral link between psychopathology and the effectiveness of postural control.

Establishing consciousness in non-communicative patients: a modern-day version of the Turing test.

In a recent study of a patient in a persistent vegetative state, [Owen, A. M., Coleman, M. R., Boly, M., Davis, M. H., Laureys, S., & Pickard, J. D. (2006). Detecting awareness in the vegetative state. Science, 313, 1402] claimed that they had demonstrated the presence of consciousness in this patient. This bold conclusion was based on the isomorphy between brain activity in this patient and a set of conscious control subjects, obtained in various imagery tasks. However, establishing consciousness in unresponsive patients is fraught with methodological and conceptual difficulties. The aim of this paper is to demonstrate that the current debate surrounding consciousness in VS patients has parallels in the artificial intelligence (AI) debate as to whether machines can think. Basically, (Owen et al., 2006) used a method analogous to the Turing test to reveal the presence of consciousness, whereas their adversaries adopted a line of reasoning akin to Searle's Chinese room argument. Highlighting the correspondence between these two debates can help to clarify the issues surrounding consciousness in non-communicative agents.

Postural responses to emotional visual stimuli.

Postural control is a motor skill that allows individuals to interact with their environment. Indeed, in all species, development of postural control is a prerequisite for acquiring further motor abilities. In humans, the maintenance of a bipedal posture plays an important role in interaction with the environment, as it provides a stable postural basis allowing upper limbs and hands to be used to manipulate objects. On the other hand, this bipedal posture induces a constraint in terms of balance, as individuals have to deal with a relatively small base of support enclosed by the surface of the two feet. Biomechanical principles underlying postural control have been studied in great depth, but the effect of emotion on postural control seems to be an emergent topic. Over the last two decades, an exponential number of studies have been published at the interface of affective and social neurosciences. Moreover, the interactions between motor and affective processes are increasingly documented in the scientific literature. In this article, we try to synthetize main recent empirical results that have allowed exploration of the link between body posture and emotional processing.

Effects of attention on the control of locomotion in individuals with chronic low back pain.

BACKGROUND: People who suffer from low back pain (LBP) exhibit an abnormal gait pattern, characterized by shorter stride length, greater step width, and an impaired thorax-pelvis coordination which may undermine functional walking. As a result, gait in LBP may require stronger cognitive regulation compared to pain free subjects thereby affecting the degree of automaticity of gait control. Conversely, because chronic pain has a strong attentional component, diverting attention away from the pain might facilitate a more efficient walking pattern. METHODS: Twelve individuals with LBP and fourteen controls participated. Subjects walked on a treadmill at comfortable speed, under varying conditions of attentional load: (a) no secondary task, (b) naming the colors of squares on a screen, (c) naming the colors of color words ("color Stroop task"), and (d) naming the colors of words depicting motor activities. Markers were attached to the thorax, pelvis and feet. Motion was recorded using a three-camera SIMI system with a sample frequency of 100 Hz. To examine the effects of health status and attention on gait, mean and variability of stride parameters were calculated. The coordination between thoracic and pelvic rotations was quantified through the mean and variability of the relative phase between those oscillations. RESULTS: LBP sufferers had a lower walking speed, and consequently a smaller stride length and lower mean thorax-pelvis relative phase. Stride length variability was significantly lower in the LBP group but no significant effect of attention was observed. In both groups gait adaptations were found under performance of an attention demanding task, but significantly more so in individuals with LBP as indicated by an interaction effect on relative phase variability. CONCLUSION: Gait in LBP sufferers was characterized by less variable upper body movements. The diminished flexibility in trunk coordination was aggravated under the influence of an attention demanding task. This provides further evidence that individuals with LBP tighten their gait control, and this suggests a stronger cognitive regulation of gait coordination in LBP. These changes in gait coordination reduce the capability to deal with unexpected perturbations, and are therefore maladaptive.

Unveiling Intermittency in the Control of Quiet Upright Standing: Beyond Automatic Behavior.

The control of posture, as in quiet upright standing, is distributed among postural reflexes and higher (cortical) centers. According to the theory of "intermittent control," the control of posture involves a rapid succession of brief periods of postural stability, during which the body dwells relatively motionless in a particular posture, and postural instability, during which the body rapidly transits to a new stable point. This theory assumes a combination of stiffness control, keeping the body in the same position, and top-down ballistic control, moving the body to a new reference position. We tested the prediction that exerting ballistic control consumes more attention, relative to stiffness control, using variations in reaction time as our index of attention load. Slower reactions to external stimulus events were expected if these events happen to coincide with ballistic control regimes compared to stiffness regimes, as unveiled from local features of the posturogram. Thirty-two participants stood on a force plate, and were instructed to press a hand-held button as soon as they heard a stimulus tone. About 40 stimuli were presented at random instances during a 3-min trial. Postural control regimes were characterized using sway-density analysis for each stimulus-response interval, by computing local dwell times from the corresponding center-of-pressure samples. We correlated stimulus-response durations with the corresponding local dwell times, and also with local velocity and local eccentricity (distance from the origin). As predicted, an overall negative correlation was observed, meaning that shorter dwell times are associated with longer stimulus-response intervals, as well as a positive correlation with local center-of-pressure velocity. The correlation between reaction times and local eccentricity was not significant. Thus, by mapping stimulus-response intervals to local center-of-pressure features we demonstrated attentional fluctuations in the control of quiet upright standing, thereby validating a core assumption underlying the notion of intermittent postural control.

Back off! The effect of emotion on backward step initiation.

The distance regulation (DR) hypothesis states that actors are inclined to increase their distance from an unpleasant stimulus. The current study investigated the relation between emotion and its effect on the control of backward step initiation, which constitutes an avoidance-like behavior. Participants stepped backward on a force plate in response to neutral, high-arousing pleasant and high-arousing unpleasant visual emotional stimuli. Gait initiation parameters and the results of an exploratory analysis of postural sway were compared across the emotion categories using significance testing and Bayesian statistics. Evidence was found that gait initiation parameters were largely unaffected by emotional conditions. In contrast, the exploratory analysis of postural immobility showed a significant effect: highly arousing stimuli (pleasant and unpleasant) resulted in more postural sway immediately preceding gait initiation compared to neutral stimuli. This suggests that arousal, rather than valence, affects pre-step sway. These results contradict the DR hypothesis, since avoidance gait-initiation in response to unpleasant stimuli was no different compared to pleasant stimuli.

Balance Performance in Autism: A Brief Overview.

Children with autism not only have limited social and communicative skills but also have motor abnormalities, such as poor timing and coordination of balance. Moreover, impaired gross motor skills hamper participation with peers. Balance control is interesting from a cognitive science perspective, since it involves a complex interplay between information processing, motor planning, and timing and sequencing of muscle movements. In this paper, we discuss the background of motor problems in children with autism, focusing on how posture is informed by sensory information processing. We also discuss the neurobiological basis of balance problems, and how this is related to anxiety in this group. We then discuss possible avenues for treatment of autism spectrum disorder (ASD) symptoms, especially as regards movement-related interventions. Finally, we present a theoretical outlook and discuss whether some of the symptoms in ASD can be understood from an embodied cognition perspective.

Evidence for Sequential Performance Effects in Professional Darts.

Objectives: The study of sequential effects in aiming tasks might shed light on the organization of repetitive motor performances over time. To date, investigations of such effects in sports have been limited and yielded mixed results. Given the relatively short time intervals between successive attempts, and the absence of defensive interventions, dart throwing provides a potentially fruitful testing ground for examining the presence of sequential performance effects in the motor domain. Methods and Results: A total of 80 competitive darts matches of 10 of the world's best players were scored from publicly available video footage in terms of sequences of hits and misses of triple 20. In darts, throws are organized in legs, i.e., a rapid succession of three throws by the same player, allowing us to investigate various transitions in performance (throw 1 → 2, 2 → 3, and 3 → 1). The resulting binary sequences were analyzed statistically in terms of independence and stationarity. Across players significant statistical evidence was found for sequential dependence from the first throw in a leg to the second throw, but not for the other transitions. As regards to stationarity, a significant decline in performance was observed in the course of the match. Conclusions: In professional darts, evidence can be found for both sequential dependence as well as for non-stationarity, implying that performance does not, or at least not always, constitute a stationary random independent process. More research is needed on the motor control mechanisms underlying the observed carry-over effects within triplets as well as the possible causes of non-stationarity.