Effects of Visual Tasks and Conversational Partner on Personal and Interpersonal Postural Activity

The control of stance is influenced by activities that are engaged in during stance. We investigated simultaneous constraints imposed by individual-specific factors (such as the distance of visual targets) and of interpersonal factors arising from dyadic conversation. Each member of participant pairs looked at targets (drawings) that were similar to, but differed from, that of a conversational partner. Conversational partners conversed to identify the differing elements. In Experiments 1 and 2, members of each dyad conversed with each other or separately conversed with a confederate (an experimenter). We varied the distance of targets (Experiment 1) and their size (Experiment 2). In Experiment 3, target size could be the same for both members of a dyad (i.e., small-small, large-large) or could differ (i.e., small-large, large-small). Interpersonal postural coordination was stronger when members of dyads conversed with each other, replicating earlier studies, but this manipulation also influenced parameters of individual sway. In Experiment 3, interpersonal postural coordination also was influenced by variation in the size of the partner's target. Analysis of the sway of individuals revealed influences of target distance and size, replicating previous effects; however, these manipulations also influenced interpersonal postural coordination. Overall, the results indicate that postural activity was modulated simultaneously with respect to individual and dyadic parameters of the task situation. We argue that it may be useful, both theoretically and empirically, to interpret the effects of conversation on postural activity within the broader context of relations between postural control and the performance of suprapostural tasks.     

Intersegmental strategies in frontal plane in moderately-skilled riders analyzed in ridden and un-mounted situations

The symmetry of the rider is highly relevant, and in the equestrian community it is generally thought that a symmetrical rider has a better possibility to influence the horse in an optimal way. The aim of the study was to analyse and compare frontal plane kinematics of the core body segments in ten riders while riding and while rocking a balance chair from side-to-side. It was hypothesized that the riders were asymmetrical in relation to their intersegmental strategies when comparing between left and right directions and that individual riders would display the same postural strategies when riding and when rocking the balance chair. Ten moderately-skilled riders wore a full-body marker set that was tracked by a motion capture system as they rocked a balance chair from side to side. Inertial measurement units attached to the head, trunk and pelvis were used to measure the segmental movements while riding in left and right directions. Roll rotation data for head, trunk and pelvis were averaged over available strides/cycles. Results from mixed models showed that the riders were asymmetric when comparing riding in left vs right directions, for example the trunk was rotated 19° to the right on the right circle and 14° to the left on the left circle, on average. Riders adopted the same asymmetrical posture whether they were riding in the left or right direction on straight lines, circles or leg yielding. A significant relationship was found between postural asymmetries when riding and when rocking the balance chair, one degree of pelvis or head roll asymmetry on the chair predicted 2.4 (SE 0.9) degrees of asymmetry while riding. Future studies may investigate the value of seated, off-horse postural training for improving rider symmetry and thereby equestrian performance.     

Torso movement constraint in stability of bimanual coordination

This study investigated the relation between postural movement and upper-limb coordination stability. Adults produced bimanual circles using in-phase and anti-phase coordination patterns in time to an increasing rate metronome (i.e., movement-time instruction) in the horizontal (e.g., tabletop) and vertical (e.g., "wall" perpendicular to body) planes. All participants produced the instructed in- and anti-phase patterns. Coordination stability (i.e., SD of relative phase) was larger for anti-phase than in-phase patterns in both planes; however, anti-phase coordination stability was lower in the vertical plane than in the horizontal plane. Torso movement was larger during anti-phase coordination patterns in the horizontal plane, whereas it was larger during in-phase coordination patterns in the vertical plane. These results indicate that different orientations of the same task can produce different results for stability of coordination. This information may be important for performing and learning complex motor-coordination movements (e.g., playing musical instruments).     

Does monopedal postural balance differ between the dominant leg and the non-dominant leg? A review

The interlimb postural comparison i.e., between the dominant leg and the non-dominant leg has been studied by numerous authors but their results are contradictory and do not lead to a consensus. Some studies showed no difference of postural balance between the dominant and the non-dominant leg whereas other studies concluded that the dominant and non-dominant leg exhibit different postural balance in healthy subjects and athletes. The aim was to analyse all these studies in order to identify the different factors that could facilitate or prevent the appearance of a postural difference between the dominant and non-dominant leg by means of a narrative review. Environmental and experimental conditions (e.g., difficulty and specificity of postural tasks; physiological state, expertise level and moment of season/period over career of subjects/athletes evaluated and nature of sport/physical activity practiced; techniques and methods used for measuring postural balance) in which postural balance is evaluated and intrinsic/individual factors (e.g., morphology, strength/power muscle, proprioception, hemispheric laterality) could influence the results. Thus, the influence of limb dominance on monopedal postural balance would probably be context-dependent. Mechanistic explanations are proposed to explain how each factor could act on the relationship between limb dominance and postural balance. However many mechanisms have not yet been explained and all the factors have not been identified, which suggests that further exploratory research is needed in order to understand this relationship.     

Self-sitting and reaching in 5- to 8-month-old infants: the impact of posture and its development on early eye-hand coordination

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.     

Postural orientation: age-related changes in variability and time-to-boundary

The relation between age-specific postural instability and the detection of stability boundaries was examined. Balance control was investigated under different visual conditions (eyes open/closed) and postural orientations (forward/backward lean) while standing on a force platform. Dependent variables included center of pressure variability and the time-to-contact of the center of pressure with the stability boundaries around the feet (i.e., time-to-boundary). While leaning maximally, older individuals (ages 55-69) showed increased center of pressure variability compared to no lean, while younger subjects (ages 24-38) showed a decrease. These significant differences were found only in anterior-posterior direction. No significant age-specific differences were found between eyes open and eyes closed conditions. Time-to-boundary analysis revealed reduced spatio-temporal stability margins in older individuals in both anterior-posterior and medio-lateral directions. Time-to-boundary variability, however, was not significantly different between the groups in both medio-lateral and anterior-posterior direction. These results show the importance of boundary relevant center of pressure measures in the study of postural control, especially concerning the lateral instability often observed in older adults.     

Self-Sitting and Reaching in 5- to 8-Month-Old Infants: The Impact of Posture and Its Development on Early Eye-Hand Coordination

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.     

No pain, no gain: Perceptions of calorie expenditures of exercise and daily activities

Reduction in physical activity is considered a major contributor to weight problems. Increasingly, people are expending less energy in household chores but joining fitness clubs. Do people perceive ordinary daily activities to expend less energy than exercise activities using similar amounts of calories? In the present study college students were asked to evaluate the calorie expenditure of 30 physical activities (i.e., exercises and household tasks). The household tasks were matched (in terms of caloric expenditure) to at least one exercise activity. When participants rated both exercise and daily activities, it appears that they focused on rate of caloric expenditure rather than type of activity (i.e., household task or exercise). In Study 2, college students evaluated the energy expenditure of light/leisure, moderate, and intense exercise. This emphasis concerning the benefit of intense physical activity was observed once again. College students appear to have assimilated the belief that intense physical activity expends more energy than longer sessions of lower intensity physical activity using similar amounts of calories. Perhaps one reason why people are not physically active is that they believe physical activities must be intense to be of benefit. At the same time they are automatizing household chores and, thus, become less active overall.     

Hierarchical control in redundant and non-redundant postural tasks

Prior studies of postural coordination have shown inconsistencies between hip-ankle coordination in redundant and non-redundant coordination tasks as well as predictions of the HKB model. These inconsistencies were investigated by testing the hypothesis that there are different hierarchical control structures for redundant (multiple potential task solutions) and non-redundant (a single task solution) coordination tasks (Bernstein, 1996). The transfer between a non-redundant postural tracking task and a redundant scanning task consisting of 16 hip-ankle relative phase patterns from 0° to 337.5° was investigated. The results showed that the transfer between the tasks was transitory, negative and occurred only from the non-redundant to the redundant task. This finding supports the hypothesis that inconsistencies between redundant and non-redundant coordination dynamics may be due to a hierarchical relation between control structures for the performance of these types of tasks.     

No pain, no gain: Perceptions of calorie expenditures of exercise and daily activities

Reduction in physical activity is considered a major contributor to weight problems. Increasingly, people are expending less energy in household chores but joining fitness clubs. Do people perceive ordinary daily activities to expend less energy than exercise activities using similar amounts of calories? In the present study college students were asked to evaluate the calorie expenditure of 30 physical activities (i.e., exercises and household tasks). The household tasks were matched (in terms of caloric expenditure) to at least one exercise activity. When participants rated both exercise and daily activities, it appears that they focused on rate of caloric expenditure rather than type of activity (i.e., household task or exercise). In Study 2, college students evaluated the energy expenditure of light/leisure, moderate, and intense exercise. This emphasis concerning the benefit of intense physical activity was observed once again. College students appear to have assimilated the belief that intense physical activity expends more energy than longer sessions of lower intensity physical activity using similar amounts of calories. Perhaps one reason why people are not physically active is that they believe physical activities must be intense to be of benefit. At the same time they are automatizing household chores and, thus, become less active overall.     

Effects of increasing expenditure of energy during exercise on psychological well-being in older adults

The purpose of present study was to examine the effects on psychological well-being of energy expended as a result of the exercise intervention. 33 older adults (M age=68.6 yr., SD=4.7) participated in three supervised water-based exercise sessions per week for 12 wk. Based on the relative changes in daily energy expenditure as measured by questionnaire between pre- and posttraining, the subjects were split into three groups. This classified each subject as either having experienced a relatively low change (n=11), moderate change (n= 11), or high change (n= 11) in daily energy expenditure. Our data showed that the group with the greater increase in energy expenditure as a result of exercise, when compared pre- and posttraining, improved only on Depression-Dejection on the Profile of Mood States more than did the group with low change. Consequently, we concluded that the amount of energy expended was partially related to improvement in psychological well-being.     

Coordination of complex bimanual multijoint movements under increasing cycling frequencies: The prevalence of mirror-image and translational symmetry

The present study examined the principles underlying inter and intralimb coordination constraints during performance of bimanual elbow–wrist movements at different cycling frequencies (from 0.75 Hz to 2.50 Hz). Participants performed eight coordination tasks that consisted of a combination of in-phase (IN) and/or anti-phase (AN) coordination modes between both elbows and wrists (interlimb), with isodirectional (Iso) or non-isodirectional (NonI) coordination modes within each limb (intralimb). As expected, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the mid-sagittal plane, had a powerful influence on the quality of global coordinative behavior both between and within limbs. When this principle was violated (i.e., when the anti-phase mode was introduced in one or both joint pairs), the non-isodirectional intralimb mode exhibited a (de)stabilizing role in coordination, which became more pronounced at higher cycling frequencies. However, pattern loss with increasing cycling frequency resulted not only in convergence toward the more stable in-phase patterns with the elbows and wrists but also to the anti-phase patterns (which were associated with directional compatibility of within-limb motions). Moreover, participants generally preserved their initial mode of coordination (either in-phase or anti-phase) in the proximal joints (i.e., elbows) while shifting from anti-phase to in-phase (or vice versa) with their distal joint pair (i.e., wrists). Taken together, these findings reflect the impact of two immanent types of symmetry in bimanual coordination: mirror-image and translational symmetry.     

The postural control can be optimized by the first movement initiation condition encountered when submitted to muscle fatigue

We investigated whether and how the movement initiation condition (IC) encountered during the early movements performed following focal muscle fatigue affects the postural control of discrete ballistic movements. For this purpose, subjects performed shoulder flexions in a standing posture at maximal velocity under two movement IC, i.e., in self-paced conditions and submitted to a Stroop-like task in which participants had to trigger fast shoulder flexions at the presentation of incongruent colors. Shoulder flexion kinematics, surface muscle activity of focal and postural muscles as well as center-of-pressure kinematics were recorded. The initial IC and the order in which subjects were submitted to these two conditions were varied within two separate experimental sessions. IC schedule was repeated before and after fatigue protocols involving shoulder flexors. The aim of this fatigue procedure was to affect acceleration-generating capacities of focal muscles. In such conditions, the postural muscle activity preceding and accompanying movement execution is expected to decrease. Following fatigue, when subjects initially moved in self-paced conditions, postural muscle activity decreased and scaled to the lower focal peak acceleration. This postural strategy then transferred to the Stroop-like task. In contrast, when subjects initially moved submitted to the Stroop-like task, postural muscle activity did not decrease and this transferred to self-paced movements. Regarding the center-of-pressure peak velocity, which is indicative of the efficiency of the postural actions generated in stabilizing posture, no difference appeared between the two sessions post-fatigue. This highlights an optimization of the postural actions when subjects first moved in self-paced conditions, smaller postural muscle activation levels resulting in similar postural consequences. In conclusion, the level of neuromuscular activity associated with the postural control is affected and can be optimized by the initial movement IC experienced post-fatigue. Beyond the fundamental contributions arising from these results, we point out potential applications for trainers and sports instructors.     

Relationship between extremities in motor performance

The purpose of the study was to examine the relationship between the extremities in different aspects of motor performance, including simple reaction time, choice reaction time, speed of movement, tapping speed, and coordination, i.e., speed of movement/accuracy. 186 healthy randomly selected right-handed subjects (93 men, 93 women; aged 21-70 years) were measured on a test battery of five tests for both hands and feet. Correlations between the extremities in motor performance were highest between hands (r=.71-.80, p<.001) or between feet (r=.57-.88, p<.001) depending on the complexity of response for all subjects. These relations remained at almost the same magnitude even when age was eliminated. Correlations between the upper and lower extremities were lower (r = .40-.62). Correlations between extremities were lower for one age group (21-30 years) than for all subjects (21-70 years). These results showed that the motor performance for the hands is not a very good indicator of the motor performance of the lower extremities, especially in a homogeneous age group, and it seems that the lower extremities should be studied with specific motor performance tests.     

Coordination dynamics of the horse-rider system

The authors studied the interaction between rider and horse by measuring their ensemble motions in a trot sequence, comparing 1 expert and 1 novice rider. Whereas the novice's movements displayed transient departures from phase synchrony, the expert's motions were continuously phase-matched with those of the horse. The tight ensemble synchrony between the expert and the horse was accompanied by an increase in the temporal regularity of the oscillations of the trunk of the horse. Observed differences between expert and novice riders indicated that phase synchronization is by no means perfect but requires extended practice. Points of contact between horse and rider may haptically convey effective communication between them.     

Multisensory postural control in adults: Variation in visual,haptic, and proprioceptive inputs

Maintaining balance is fundamentally a multisensory process, with visual, haptic, and proprioceptive information all playing an important role in postural control. The current project examined the interaction between such sensory inputs, manipulating visual (presence versus absence), haptic (presence versus absence of contact with a stable or unstable finger support surface), and proprioceptive (varying stance widths, including shoulder width stance, Chaplin [heels together, feet splayed at approximately 60°] stance, feet together stance, and tandem stance) information. Analyses of mean velocity of the Centre of Pressure (CoP) revealed significant interactions between these factors, with stability gains observed as a function of increasing sensory information (e.g., visual, haptic, visual + haptic), although the nature of these gains was modulated by the proprioceptive information and the reliability of the haptic support surface (i.e., unstable versus stable finger supports). Subsequent analyses on individual difference parameters (e.g., height, leg length, weight, and areas of base of support) revealed that these variables were significantly related to postural measures across experimental conditions. These findings are discussed relative to their implications for multisensory postural control, and with respect to inverted pendulum models of balance. (185 words).     

Anxiety, learning, and memory: A reconceptualization

A new theoretical framework for work on anxiety and memory is proposed. Anxious subjects engage in task-irrelevant processing which preempts processing resources and some of the available capacity of working memory. They typically attempt to compensate for the adverse effects of this task-irrelevent processing on task performance by increased effort. It follows from these theoretical assumptions that anxiety will have differential effects on performance efficiency (i.e., the quality of performance) and on processing effectiveness (i.e., performance efficiency/effort). Anxiety will always reduce processing effectiveness, but will not impair performance efficiency if there is sufficient effort expenditure. Consequently, reliance on measures of performance efficiency will often obscure the detrimental effects of anxiety on processing effectiveness.     

Linear versus Hierarchical Agreement Feature Processing in Comprehension

Two experiments examined whether syntactic number features are tracked during comprehension with a linear slot-based memory system or with a hierarchical feature-passing system. In a construction such as The pond near the trail(s) for the horse(s) was ¨, a linear account of subject-number tracking predicts greater interference from horses (N3), whereas a hierarchical account predicts greater interference from trails (N2). Experiment 1 used singular-head subject noun phrases (e.g., pond) and showed equal interference from N2 and N3, failing to differentiate between linear and hierarchical accounts. Experiment 2 used plural-head subjects and revealed more interference from N2 than N3. The pattern across the experiments accords with the ideas that (1) feature-tracking is hierarchical (e.g., Vigliocco & Nicol, 1997), (2) plurals are marked (e.g., Eberhard, 1997), and (3) subject-number information decays across intervening number-marked elements.     

Predictors of perceived road collision/incident risk among horse users: A survey study from Norway

Although horse users in traffic are a vulnerable road user group, traffic safety problems among them are scantly examined by previous research. The main aim of the present study was to examine the role of some demographic variables, traffic safety attitudes, and level of knowledge about rules and regulations applying to horse use in traffic for predicting perceived road collision/incident risk in a sample of horse users in Norway. An online survey was conducted to collect data from a total of 1733 horse users including horse riders and drivers of horse-drawn sulky, wagon or sled. The respondents accessed the survey via a link put to the website of the Norwegian Horse Centre, which is in contact with many different horse user environments in Norway. The majority of the respondents were female and between the ages of 18–30. A multiple regression analysis was conducted to examine the predictors of the perceived collision/incident risk involving other motor vehicles. Results showed that traffic safety attitudes among horse users were the strongest predictor of the perceived collision/incident risk. In particular, horse users reported a negative attitude towards the other road users (e.g. drivers) indicating that they perceive the other road users’ actions and approaches as the biggest source of risk in road traffic. The level of knowledge about the rules and regulations applying to horse use, especially in walking and cycling lane, was relatively low among the respondents. However, knowledge about rules and regulations did not appear as a strong predictor of the perceived collision/incident risk. Results indicate the need to increase road users, especially drivers’, awareness about the problems and needs of horse users in traffic.     

Attentional load associated with performing and stabilizing a between-persons coordination of rhythmic limb movements

This study addressed the issue of intentional stabilization of between-persons coordination patterns (in-phase/isodirectional and anti-phase/non-isodirectional) and the attentional cost incurred by the nervous system in maintaining and further stabilizing these coordination patterns. Five pairs of participants performed in-phase and anti-phase interpersonal coordination patterns in dual-task conditions (coordination+RT task). Results showed that: (1) isodirectional pattern (in-phase) was more stable than non-isodirectional pattern (anti-phase), (2) both iso- and non-isodirectional pattern were stabilized intentionally, (3) RT was lower for the isodirectional pattern (i.e., the most stable), and (4) attentional manipulation led to a trade-off between pattern stability and RT performance. These results suggest that performing between-persons coordination patterns incurs a central cost that depends on the coupling strength between the limbs. These findings are consistent with the previous studies in intrapersonal coordination.