Computing the COM from the COP in postural sway movements

A method is described for computing the centre of mass (COM) from empirical estimates of the centre of pressure (COP) obtained by means of a force platform. The method is based on a biomechanical model of sway movements in quiet standing, according to which the horizontal acceleration of the COM is approximately proportional to the COM–COP difference. The equations are solved by approximating the solution with best fitting spline functions. The implications for movement control are discussed.     

Vis‐à‐vis the Couch: Where is Psychoanalysis?

The author discusses ways in which the couch or chair (lying down versus sitting up) may be used to maintain safety and defend against perceived dangers in the analytic process. Several dialectics are relevant as they intersect with that of danger and safety, including engagement/privacy, interiority/exteriority and subject/object. The author discusses these dialectics in terms of the ways in which the analyst is used at different points in time, i.e. as an objectifi ed other, a subjective object or part-object, or as a subject with an internal world. The therapeutic action associated with sitting up (versus lying down on the couch) has been undertheorized, despite the fact that many, if not most, analysands sit up for some portion of their analysis. Through the use of a heuristic visual-spatial metaphor as represented by the use of the couch or chair, the author discusses the signifi cance of lying down and sitting up for therapeutic action.     

姿势干扰强度的心理预期效应

本研究基于经典快速举臂试验与落球试验范式, 采用表面肌电信号分析技术, 研究内、外姿势干扰强度的心理预期对腰部姿势肌肉和上肢动作肌肉预期姿势调节(APAs)和补偿姿势调节(CPAs)的影响, 探讨中枢神经系统(CNS)对内、外姿势干扰的控制策略。20名健康受试者先后完成不同负荷强度的快速举臂试验和落球试验, 同步采集腰部竖脊肌、腰部多裂肌和上肢肱二头肌的表面肌电信号, 计算肌肉预激活时间和APAs与CPAs积分肌电值, 观察内、外姿势干扰强度的心理预期对中枢APAs和CPAs控制机制的影响。结果显示内部姿势干扰条件下, 干扰强度的心理预期对腰部多裂肌、腰部竖脊肌和上肢肱二头肌的APAs强度有显著影响, 而对预激活时间和CPAs强度无显著影响; 外部姿势干扰条件下, 干扰强度的心理预期对腰部多裂肌、腰部竖脊肌和肱二头肌的APAs强度有显著影响, 对肱二头肌和腰部多裂肌预激活时间有显著影响, 而对CPAs强度无显著影响。突发可预期姿势干扰条件下姿势的快速反应是一个由CNS主导的神经肌肉运动控制过程。受姿势干扰强度心理预期的影响, CNS对内、外突发姿势干扰条件下腰部姿势肌肉的活动采取了不同的控制策略。在内部姿势干扰条件下, 干扰刺激发生时间明确, CNS主要通过对APAs强度的调节来实现姿势肌肉的优化控制; 而在外部姿势干扰条件下, 干扰刺激时间不明确, CNS则通过对局部稳定肌APAs预激活时间以及局部稳定肌和整体稳定肌APAs强度的双重调节实现姿势肌肉的优化控制。干扰强度的心理预期对姿势肌肉APAs和CPAs的作用表明, 心理预期效应主要源自于CNS对局部和整体稳定肌APAs控制机制的调制。     

Short-Term Repeatability of Stabilometric Assessments

The authors evaluated the short-term (within-day, between-days) repeatability of center of pressure (COP) displacements. COP sway area and speed were obtained in the morning and afternoon of two separate days, both with open (EO) and closed (EC) eyes, in 10 healthy adults. Agreement and variability among conditions were tested by ANOVA and Bland-Altman plots. Mode (EO/EC, area: p = .032; speed: p < .004), and day (day1/day2, area: p = .006; speed: p = .02) showed significant differences. The EC condition and the second test day showed the largest values, with medium-large effect sizes. Time-of-day did not influence COP displacements. Speed had better agreement than area (Bland-Altman plots). COP displacements were well reproducible within-day, but had significant between-days variations. COP assessments should be performed in the same session.     

A Cognitive-Behavioral Model of Persistent Postural-Perceptual Dizziness

Persistent postural-perceptual dizziness (PPPD; previously termed “chronic subjective dizziness”) is a frequently observed disorder in patients who present with dizziness to audiology; ear, nose, and throat; or neurology clinics. The primary symptoms are persistent nonvertiginous dizziness, and hypersensitivity to motion and visual stimuli. These occur either in the absence of any active neuro-otologic illness or, where an episodic vestibular disorder exists, symptoms cannot be fully explained by the disorder alone. Diagnosis is necessarily multidisciplinary and proceeds by identification of primary symptoms and exclusion of other neurological or active medical disorders requiring treatment. Psychological processes are implicated in the development and maintenance of PPPD, with similarities to cognitive models of health anxiety and panic disorder, and there is evidence that cognitive-behavioral therapy is an effective treatment. A cognitive-behavioral model of PPPD is presented along with a case example. It is suggested that dizziness becomes persistent when it is processed as a threat, and that it is maintained by (a) unhelpful appraisals, (b) avoidance and safety behaviors, and (c) attentional strategies including selective attention to body sensations associated with dizziness. Once PPPD is identified techniques for its effective treatment fall within the skills mix of qualified cognitive-behavioral therapists or vestibular clinical scientists who have received additional training in cognitive and behavioral treatment.     

Age-related Changes in Postural Sway During Sit-to-stand in Typical Children and Children with Cerebral Palsy

Objective: To assess age-related changes in postural sway during sit-to-stand (STS) in typical children (TC) and children with mild cerebral palsy (CP). Methods: Thirty-five TC and 23 children with mild CP were allocated in four different age groups: 5–6, 7–9, 10–12, and 13–15 years; they all performed STS movements over a force plate. Anterior-posterior and medial-lateral amplitude of center of pressure (CoP) displacement, area and velocity of CoP sway were analyzed and compared between the age groups for TC and children with CP. Results: TC at 5 to 6 years of age showed higher values of anterior-posterior CoP displacement and Area of CoP sway than at 10–12 years, during the stabilization phase. There were no age-related changes for CP. Conclusion: TC change their postural sway during the last STS phase over the years, reducing their body sway. Children with CP did not show age-related changes in sway during STS, reflecting a distinct rhythm of postural control development in this population.     

The Influence of Motor Imagery on Postural Sway: Differential Effects of Type of Body Movement and Person Perspective

The present study examined the differential effects of kinesthetic imagery (first person perspective) and visual imagery (third person perspective) on postural sway during quiet standing. Based on an embodied cognition perspective, the authors predicted that kinesthetic imagery would lead to activations in movement-relevant motor systems to a greater degree than visual imagery. This prediction was tested among 30 participants who imagined various motor activities from different visual perspectives while standing on a strain gauge plate. The results showed that kinesthetic imagery of lower body movements, but not of upper body movements, had clear effects on postural parameters (sway path length and frequency contents of sway). Visual imagery, in contrast, had no reliable effects on postural activity. We also found that postural effects were not affected by the vividness of imagery. The results suggest that during kinesthetic motor imagery participants partially simulated (re-activated) the imagined movements, leading to unintentional postural adjustments. These findings are consistent with an embodied cognition perspective on motor imagery.     

Study of a cognitive effects model in Dohsa‐hou for the elderly

This study investigates the primary factors responsible for cognitive performance improvements as a result of dohsa‐hou (Japanese body‐oriented psychotherapy) for the elderly. The study divided participants into two homogeneous groups: an experimental group that attempted to improve upright balance by performing dohsa‐hou, and a control group to establish the drop‐off period for the effect of performing the given activities. The task processing time of Stroop Test and body sway and the situational anxiety during task processing of Stroop Tests were measured before and after the dohsa‐hou and drop‐off period. The results confirm that only the experimental group improved in body sway, had a shorter Stroop Color Test processing time and lower situational anxiety. From this study, it has been identified that: (a) information‐processing capacities spared for posture control are affected by distribution of processing resources towards solving other cognitive tasks; and (b) the effect of the release of attention from threat‐related information due to a decrease in attentional bias, which accompanied the decrease in situational anxiety, are primary factors in improving cognitive task performance.     

The Influence of an Acute Bout of Whole Body Vibration on Human Postural Control Responses

The use of vibrating platforms has become increasingly available, and popular at sports and rehabilitation institutes. Given the discrepancies in the literature regarding whole body vibration (WBV) and human reflexive responses, the purpose of this study was to examine the acute effects of WBV on postural response latencies, as well as associated electromyography measures of the lower extremities during balance perturbations. Reflexive responses during backward and forward balance perturbations were examined before, after, and 10 min after a bout of WBV. The findings suggest that following an acute bout of whole body vibration, muscle activity of the lower extremities is decreased during a reflexive response to an unexpected perturbation, and may be associated with faster reaction time.     

Effects of Visual Manipulation in Sit-to-Stand Movement in Children With Cerebral Palsy

The authors sought to verify the effects of vision on sit-to-stand (STS) movement performance by means of postural sway in children with cerebral palsy (CP) and typical children (TC). Participants were 42 TC and 21 children with CP. STS movement was assessed with eyes open and with eyes closed. Area and velocity of center of pressure sway were analyzed in each of the 3 STS phases. We observed greater postural sway during STS movement with eyes closed. Children with CP presented greater postural sway than TC did. Both groups exhibited greater postural instability with absence of vision expressing the role of vision to keep postural stability. Moreover, the greater postural instability was observed in children with CP.