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Playful approaches are recommended to enhance wheelchair skills training with young people. Inclusive dance allows participants to discover motor skills and improve social participation. Integrating wheelchair skills training into dance has not been evaluated. This study aimed to explore participants' experiences in dance while integrating wheelchair skills, and the influence of dance on wheelchair skills and wheelchair use confidence in young people. A convergent mixed-methods design was used during a one-week dance camp. Data collection combined observations, two focus groups (with young dancers who used manual wheelchairs and with professional dancers without disabilities), and evaluation of wheelchair skills and confidence. Data analyses included deductive thematic analysis guided by the Quality Parasport Participation Framework, merged with pre–post comparisons in wheelchair skills and confidence. Three young female dancers were 11, 12 and 15 years of age and three professional female dancers were 22, 27 and 27 years of age. Emergent themes included skill mastery, belongingness, and supportive environments. There were improvements in wheelchair skills and confidence (16.7%, 19.4%, 16.7%; 0.8%, 11.4%, 4.5%, respectively). Participants described overall positive experiences with the dance camp and perceived enhanced skills and confidence. This study advances knowledge about innovative approaches to integrate wheelchair skills training for young people. Future larger-scale controlled studies are needed to determine efficacy. [ABSTRACT FROM AUTHOR]

Situating prehistoric sites in their past environment helps us to understand their functionality and the organization of early sedentary human societies. However, this is a challenge as the natural environment constantly evolves through time and erases these constructions, especially along riverbanks, thus biasing the archaeological record. This study introduces a reassessment of the paleo-landscape evolution around the Neolithic enclosures at the Noyen-sur-Seine site based on new field observations as well as the synthesis of (un)published and new radiocarbon dating. Contrary to the initial hypothesis, our results show that the Noyen enclosures were not built along a Neolithic Seine River: the nearby channels were active in the Middle Age and Early Modern periods. Therefore, the results show that the enclosures were originally much larger: only a fraction that survived river erosion (lateral migration rates up to 2–3 m yr−1 estimated during the nineteenth century) has been preserved. Instead, an abandoned Mesolithic Seine River served as a natural delimitation of the SE part of the Neolithic enclosures. These results indicate that Neolithic enclosures in alluvial settings are often only partly preserved and that societies from that period lived farther away from active rivers than originally thought, where they were protected from floods. [ABSTRACT FROM AUTHOR]

Situating prehistoric sites in their past environment helps us to understand their functionality and the organization of early sedentary human societies. However, this is a challenge as the natural environment constantly evolves through time and erases these constructions, especially along riverbanks, thus biasing the archaeological record. This study introduces a reassessment of the paleo-landscape evolution around the Neolithic enclosures at the Noyen-sur-Seine site based on new field observations as well as the synthesis of (un)published and new radiocarbon dating. Contrary to the initial hypothesis, our results show that the Noyen enclosures were not built along a Neolithic Seine River: the nearby channels were active in the Middle Age and Early Modern periods. Therefore, the results show that the enclosures were originally much larger: only a fraction that survived river erosion (lateral migration rates up to 2–3 m yr−1 estimated during the nineteenth century) has been preserved. Instead, an abandoned Mesolithic Seine River served as a natural delimitation of the SE part of the Neolithic enclosures. These results indicate that Neolithic enclosures in alluvial settings are often only partly preserved and that societies from that period lived farther away from active rivers than originally thought, where they were protected from floods. [ABSTRACT FROM AUTHOR]

Power training (PT) is a promising training modality to improve functional abilities in children with cerebral palsy (CP). This study aimed to implement PT in an adapted school and to assess its effect on locomotion capacities in children with Gross Motor Function Classification System (GMFCS) level III–IV. Nine children with CP (GMFCS level III–IV) were trained three times/week for 12 weeks. The training sessions took place during the 50-minute physical activity classes and included high intensity exercise. The outcome measures were the performance on the 10-meter comfortable and fast walking tests, the 50-meter sprint test (50M-ST), and the energy expenditure index (EEI). Participants spent 12 ± 7 and 7 ± 9 min per session at an intensity superior to 40% and 60% of the heart rate reserve, respectively. Performance in the 10-meter walking test (13.5 ± 7.8 to 9.9 ± 4.6 s, p < 0.05), the 10-meter fast walking test (8.8 ± 3.1 to 7.0 ± 3.2 s, p < 0.05), the 6-minute walking exercise (199.0 ± 48.6 to 316.6 ± 107.2 m, p < 0.05), and in 50M-ST (53.8 ± 29.5 to 42.3 ± 16.2 s, p < 0.05) increased after training. The EEI was reduced after training (p = 0.01), resulting in a more efficient gait. PT was successfully implemented in children with CP with GMFCS level III–IV. Results suggest that PT increases walking capacities. Power training (PT) is feasible with children with bilateral cerebral palsy with GMFCS level III and IV. Physical education course in specialist school is a valuable environment to implement PT in children with poor gross motor function. Power training results in locomotion capacities improvement. [ABSTRACT FROM AUTHOR]

Evaluate the relationship between different walking capacities and muscle strength in children with bilateral cerebral palsy (BCP) and assess these relationships in stronger and weaker children. Thirty-two children with spastic BCP were included. All participants walked under three speed conditions: comfortable, fast, and for a longer period (6 min). Walking speeds, Energy Expenditure Index (EEI), and lower limb muscle strength were measured. A global strength index (GSI) was computed as the sum of each muscle group strength. Pearson's coefficient and regression models were computed between walking capacities and the GSI. GSI was correlated with the EEI and all walking speeds. Logarithmic regressions models explained between 24 and 34% of the variance of walking capacities. Then, the group was divided in two subgroups (weaker and stronger children). GSI was correlated with comfortable and endurance waking speed in weaker children, but not in stronger children. This study reports logarithmic relationship between muscle strength and walking capacities in children with BCP. The subgroup analysis implies that muscle strength has an impact on walking capacities solely in weaker children, suggesting that muscle strength must be preserved and reinforced in interventions targeting motor function in weaker children with BCP. In a sample of children with spastic bilateral cerebral palsy, this study shows that global muscle strength is associated with walking capacities and the relationship seems more complex than linear. Based on the results, interventions should focus on maintaining or improving muscle strength in weaker children as no association was observed between muscle strength and walking capacities in stronger children. In stronger children, intervention should focus on factors other than muscle strength as it does not influence walking capacities. Based on this study, a more accurate screening of children who could benefit from strength training could be completed by initial global muscle strength. [ABSTRACT FROM AUTHOR]

Assessing the contribution of geomorphic processes to the (non‐)preservation of sedimentary deposits is necessary to account for potential bias in measured accumulation rates in the stratigraphic record. In this study, a series of numerical simulations of fluvial meandering successions is performed using FLUMY, a model of channel motions and sedimentary facies deposition. We develop tools to measure non‐deposition (stasis S) and reworking (R) of previously deposited sediment between iterations, which are both generators of hiatuses in the sedimentary record. We then compare S and R with measurements of accumulation rates and completeness (C). Results show that combining measurements of both topographic and facies changes allows for a better record of surface evolution than measuring topographies only. Accumulation rate dependence on measurement time span allows distinguishing between two regimes. The first one (anti‐persistent) is characteristic of channel avulsion and compensational stacking until the whole domain is visited by overbank deposition, corresponding to the visitation timescale Tv. In the second regime (persistent), reworking by channel migration is the remaining active process until the whole system has aggraded one channel depth, corresponding to the compensation timescale Tc. Based on these results, we propose a new simple formulation based on stasis and reworking to estimate average completeness. Plain Language Summary: Sedimentary rocks contain a record of Earth's past environments and evolution, which has a lot of missing information. This is due to sedimentary processes dynamics. In the case of fluvial systems, deposition is limited to the area near rivers while the remaining landscape is "inactive." With time, rivers move to other locations, which accumulate sediment, whereas abandoned area do not anymore. In addition, river channels are erosive and can remove previously accumulated sediment: part of the record is then lost. The greater the recording time, the more information is missing. This study explores the factors that have an influence on time preservation in rocks in the case of meandering rivers deposits. To that purpose, we use a numerical model of a river‐swept alluvial plain. We track changes of the depositional record with time using several indicators: the sediment deposition rates, the fraction of inactive surface and the fraction of erased record. Compared to previous studies, we measure changes of the sediment record between iterations in addition to measures of topographic change, which gives better results to assess time preservation. This leads us to propose a new formulation for estimating the average time preservation in sedimentary records. Key Points: Fluvial meandering simulations used to track topographic and facies changes to resolve the influence of stasis and reworking on completenessTimescale for visiting the floodplain corresponds to the transition from anti‐persistent to persistent depositional regimesNew simple formulation to assess average completeness [ABSTRACT FROM AUTHOR]

Purpose: Cerebral palsy is a neurological disorder not only affecting motor functions but also cognitive and psychosocial dimension. Multispecialty therapies are needed to address these dimensions. Dance practice provides multidimensional benefits for people with various neurological disorders and may present a real potential for people with cerebral palsy. A scoping review is conducted to evaluate the impact of dance in children and adults with cerebral palsy, based on the Human Development Model–Disability Creation Process 2 and its three key concepts: personal factors, environmental factors and life habits. Materials and methods: Studies were selected based on a systematic search of published literature in the following databases PubMed, Medline, EBM Reviews, EMBASE and CINAHL. Studies addressing any concepts on the impact of dance training on motor, cognitive and psychosocial dimensions in people with cerebral palsy were included. Results: Seven studies representing 45 children and 12 adults with cerebral palsy were selected. They had heterogeneous populations, protocols and outcomes measures, but overall covered the three main concepts of the model. Dance may have both motor and social benefits although the evidence remains weak. Conclusions: Dance appears to be a promising activity for people with cerebral palsy. Recommendations are proposed for future studies. Cerebral palsy affects motor and cognitive functions and has social repercussions. Dance can be a promising activity for people with a cerebral palsy. Dance may have both motor and social benefits although the evidence remains weak. [ABSTRACT FROM AUTHOR]

Cerebral palsy (CP) impacts motor functions such as balance, limits of stability and walking, and may also affect other functions such as attention and rhythm production. Motor and non-motor deficits lead to difficulties in daily life activities. The main objective of this study was to evaluate the effects of a dance intervention on balance in adolescents with CP. The secondary objectives were to evaluate the effects of this intervention on walking speed, attention, and rhythm production. A pre-post design study with a double baseline was conducted on ten adolescents with CP in order to assess the effects of a 10-week dance intervention. The dance intervention focused on improving balance and limits of stability. Outcomes on static and dynamic balance were evaluated with clinical and laboratory tests before and after the intervention. Walking speed, attention, and rhythm production were also evaluated before and after the intervention. Balance improved after the dance intervention as assessed with both the clinical tests and a laboratory test. Rhythm production also improved after the dance intervention. Results suggest that a 10-week dance intervention is an effective activity to improve static and dynamic balance as well as rhythmic production in adolescents with CP. [ABSTRACT FROM AUTHOR]

Pointing to a visual target that disappears prior to movement requires the maintenance of a memory representation about the location of the target. It has been shown that a target can be stored egocentrically, allocentrically, or in both frames of reference simultaneously. The main goal of the present study was to compare the accuracy and kinematics of a pointing movement to a remembered target when egocentric, allocentric, or combined egocentric and allocentric coding was possible. The task was to localize, memorize, and reach to a remembered target. Condition 1 was the ‘no-context’ condition and involved presenting the target in a completely dark environment (egocentric condition). For 2 other conditions, the target was presented within a visual context provided by an illuminated square. Condition 2 was the ‘stationary-context’ condition and involved keeping the context at the same position during the whole trial (egocentric and/or allocentric coding). Condition 3 was a ‘moved-context’ condition that involved shifting the context to a different location during the recall delay (allocentric coding). Movement accuracy and kinematics results were strikingly similar for the moved-context and stationary-context conditions. These results suggest that when both allocentric and egocentric coding are possible, an allocentric strategy is used. [ABSTRACT FROM AUTHOR]

Purpose: Past research with JACO has principally focused on the short-term impacts on new users. Therefore, this study aims to document the long-term impacts of this assistive device on users and their family caregivers following prolonged use. Methods: Users' characteristics, caregivers' characteristics and expenses related to JACO were documented with questionnaires designed for this study. Upper extremity performance was measured with an adaptation of an upper extremity performance test, the TEMPA, and accomplishment of life habits was documented in an interview based on the LIFE-H questionnaire. Satisfaction with JACO and psychosocial impacts of its use were measured with validated questionnaires, namely the QUEST and the PIADS-10. Impacts of JACO on family caregivers were documented with a validated questionnaire, the CATOM. Descriptive statistics were used to report the results. Results: Seven users and five caregivers were recruited. One user had expenses related to JACO in the past two months. Users had a better upper extremity performance with JACO than without it and they used their robotic arm to accomplish certain life habits. Most users were satisfied with JACO and the psychosocial impacts were positive. Impacts on family caregivers were slight. Conclusions: JACO increased performance in manipulation and facilitated the accomplishment of certain life habits. Users' increased participation in their life habits may slightly decrease the amount of caregiver assistance required. Future studies are needed to clarify its economic potential, its impact on caregivers' burden, including paid caregivers, and the variability in the tasks performed using JACO. The use of JACO may have positive impacts on its users in terms of upper extremity performance, accomplishment of life habits, satisfaction with the device and psychosocial impacts. More research is needed to quantify more accurately the economic potential of the long-term use of JACO, to explore the factors related to the variability in the tasks performed using JACO, and to clarify the impact of JACO on caregivers' burden, including paid caregivers. [ABSTRACT FROM AUTHOR]

Purpose: To: 1) characterize the overall experience in using the McGill immersive wheelchair - community centre (miWe-CC) simulator; and 2) investigate the experience of presence (i.e., sense of being in the virtual rather than in the real, physical environment) while driving a PW in the miWe-CC. Method: A qualitative research design with structured interviews was used. Fifteen clinicians and 11 children were interviewed after driving a power wheelchair (PW) in the miWe-CC simulator. Data were analyzed using the conventional and directed content analysis approaches. Results: Overall, participants enjoyed using the simulator and experienced a sense of presence in the virtual space. They felt a sense of being in the virtual environment, involved and focused on driving the virtual PW rather than on the surroundings of the actual room where they were. Participants reported several similarities between the virtual community centre layout and activities of the miWe-CC and the day-to-day reality of paediatric PW users. Conclusion: The simulator replicated participants' expectations of real-life PW use and promises to have an effect on improving the driving skills of new PW users. Implications for rehabilitation: Among young users, the McGill immersive wheelchair (miWe) simulator provides an experience of presence within the virtual environment. This experience of presence is generated by a sense of being in the virtual scene, a sense of being involved, engaged, and focused on interacting within the virtual environment, and by the perception that the virtual environment is consistent with the real world. The miWe is a relevant and accessible approach, complementary to real world power wheelchair training for young users. [ABSTRACT FROM AUTHOR]

Background. Robotic arms may help users perform various activities. Even though robotic arms are commercially available, their impacts are still poorly understood. Purpose. This scoping review aimed to identify the potential impacts of using robotic arms for individuals with upper-extremity disabilities and appraise the scientific quality of the selected studies. Method. A search for studies published between 1970 and 2016 was conducted in PubMed, Embase, Compendex, and Scopus. The Canadian Model of Occupational Performance and Engagement was used to classify activities in which impacts were evaluated. The quality of each study was rated using McMaster University's critical review form for quantitative studies. Findings. Thirty-six studies were reviewed, which evaluated self-care (21), productivity (33), and leisure (8). The short-term impacts were more commonly documented than long-term impacts. The impacts identified were mostly positive. The studies' mean quality score was 8.8/15. Implications. Additional studies with more rigorous conditions are needed to produce higher-quality scientific evidence of the long-term impacts of robotic arm use. [ABSTRACT FROM AUTHOR]

Weight shifting is a key ability to both train and monitor in rehabilitation processes. In the last decade, active video game consoles (AVGC) have been viewed as a promising and appealing way to facilitate weight shifting ability. However, to date, no commercially available AVGC have been specifically developed for balance and postural control throughout rehabilitation processes. The present study aims to establish a proof of concept about the possibility to integrate into a unique AVGC, a board, monitoring the player centre of pressure, and a Kinect, which takes into account the postural movement and player motor function capacity. [ABSTRACT FROM AUTHOR]

Background: Joint torques are generally of primary importance for clinicians to analyze the effect of a surgery and to obtain an indicator of functional capability to perform a motion. Given the current need to standardize the functional evaluation of the upper limb, the aim of this paper is to assess (1) the variability of the calculated maximal elbow joint torque during cyclic elbow flexion-extension movements and (2) participant test-retest repeatability in healthy young adults. Calculations were based on an existing non-invasive method including kinematic identification and inverse dynamics processes. Methods: Twelve healthy young adults (male n = 6) performed 10 elbow flexion-extension movement carrying five different dumbbells (0, 1, 2, 3 and 4 kg) with several flexion-extension frequencies (½, 1/3, ¼ Hz) to evaluate peak elbow joint torques. Results: Whatever the condition, the variability coefficient of trial peak torques remained under 4 %. Bland and Altman plot also showed good test-retest, whatever the frequency conditions for the 0, 1, 2, and 3 kg conditions. Conclusion: The good repeatability of the flexion-extension peak torques represents a key step to standardize the functional evaluation of the upper limb. [ABSTRACT FROM AUTHOR]

The goal of this study was to determine the repeatability of gait parameters measured by a force plate gait analysis system (Leonardo Mechanograph®GW) in healthy children. Nineteen healthy children and adolescents (age range: 7–17 years) walked at a self-selected speed on an 11-m-long walkway. Vertical ground reaction forces were measured in the central 6 m of the walkway. Each participant performed three blocks of three trials while walking barefoot and three blocks of three trials while wearing shoes. There were no differences between trials within each condition. All force and spatiotemporal parameters had intraclass correlation coefficients above 0.87 and coefficients of variation in the order of 1–6%. In this group of healthy children and adolescents, gait analysis with a force plate system produced repeatable intra-day results. [ABSTRACT FROM AUTHOR]

Background. Children with cerebral palsy (CP) are prone to secondary complications related to physical inactivity and poor cardiorespiratory capacity. This problem could be greatly attenuated through the use of video games that incorporate physical activity for 2 reasons: Video games already represent an important component of leisure time in younger people, and such games can lead to a high level of exercise intensity in people who are healthy. Objective. The study objective was to evaluate exercise intensity in children with spastic diplegic CP and children who were typically developing while playing with an active video game console. Design. This was a cross-sectional study. Methods. Ten children (7–12 years old) with spastic diplegic CP (Gross Motor Function Classification System level I or II) and 10 children who were age matched and typically developing were evaluated in a movement analysis laboratory. Four games were played with the active video game console (jogging, bicycling, snowboarding, and skiing) for 40 minutes. Heart rate was recorded during the entire playing period with a heart rate belt monitor. Exercise intensity was defined as the percentage of heart rate reserve (HRR). In addition, lower extremity motion analysis was carried out during the final minute of the playing period for the jogging and bicycling games. Results. No difference between groups was observed for any variables. A main effect of games was observed for the amount of time spent at an intensity greater than 40% of HRR. Specifically, more than 50% of the playing time for the jogging game and more than 30% of the playing time for the bicycling game were spent at an intensity greater than 40% of HRR. In addition, the jogging game produced a larger range of motion than the bicycling game. Limitations. A limitation of this study was the relatively small and heterogeneous sample. Conclusions. For all 4 games, similar exercise intensity levels were observed for children who were typically developing and children with CP, suggesting that children with CP could obtain exercise-related benefits similar to those obtained by children without CP while playing with an active video game console. INSET: The Bottom Line. [ABSTRACT FROM AUTHOR]

Objective: To evaluate sustained attention in adolescents with cerebral palsy (CP). CP affects motor control as well as certain cognitive processes such as attention, but its influence on the latter remains largely unexplored. Methods: Manual (Experiment 1) and oculomotor (Experiment 2) versions of the Continuous Performance Test were performed by adolescents with spastic CP and healthy age-matched controls ( n = 10 per group in each experiment). Results: In both experiments, patients with CP showed more omissions and their reaction time was more variable than controls. In Experiment 2, patients also showed more commissions. This problem was not observed in Experiment 1, possibly because of the presence of a hand movement deficit in CP. Conclusion: Taken together, the results show that sustained attention and inhibition capabilities are affected in CP. The present study also proposes that eye movements could constitute an interesting alternative for measuring sustained attention when hand movement is affected. [ABSTRACT FROM AUTHOR]

Purpose. To evaluate the effect and feasibility of a 10-week group aquatic training programme on gait efficiency in adolescents with cerebral palsy (CP). The secondary purpose was to determine the exercise intensity during aquatic training in a heterogeneous group of adolescents with CP and to investigate the impact of the training programme on the musculoskeletal system. Method. Twelve ambulatory adolescents with spastic CP were recruited. They participated in 20 aquatic training sessions (45 min twice a week). Three physical therapists and a sports teacher supervised the training sessions. Participants wore a heart rate monitor to assess sessions' intensity and a floatation device as appropriate. The primary outcome measure was gait efficiency as measured by the gait energy expenditure index (EEI). The secondary measures were (1) gait spatiotemporal parameters, (2) maximal isometric knee strength and (3) gross motor function. Results. Ten adolescents completed the training programme. No adverse effect was reported. Average exercise intensity was mild to moderate for more than half of the training session. A significant reduction of the EEI and the heart rate during walking was observed following the training programme. No significant change was observed on secondary outcome measures. Conclusions. Group aquatic training increases gait efficiency in adolescents with CP. This improvement is related to systemic cardiorespiratory adaptations. Group aquatic training programme is feasible in adolescents presenting CP at different levels of severity. [ABSTRACT FROM AUTHOR]

Chunking of single movements into integrated sequences has been described during motor learning, and we have recently demonstrated that this process involves a dopamine-dependant mechanism in animal (Levesque et al. in Exp Brain Res 182:499–508, ; Tremblay et al. in Behav Brain Res 198:231–239, ). However, there is no such evidence in human. The aim of the present study was to assess this question in Parkinson’s disease (PD), a neurological condition known for its dopamine depletion in the striatum. Eleven PD patients were tested under their usual levodopa medication (ON state), and following a 12-h levodopa withdrawal (OFF state). Patients were compared with 12 healthy participants on a motor learning sequencing task, requiring pressing fourteen buttons in the correct order, which was determined by visual stimuli presented on a computer screen. Learning was assessed from three blocks of 20 trials administered successively. Chunks of movements were intrinsically created by each participant during this learning period. Then, the sequence was shuffled according to the participant’s own chunks, generating two new sequences, with either preserved or broken chunks. Those new motor sequences had to be performed separately in a fourth and fifth blocks of 20 trials. Results showed that execution time improved in every group during the learning period (from blocks 1 to 3). However, while motor chunking occurred in healthy controls and ON-PD patients, it did not in OFF-PD patients. In the shuffling conditions, a significant difference was seen between the preserved and the broken chunks conditions for both healthy participants and ON-PD patients, but not for OFF-PD patients. These results suggest that movement chunking during motor sequence learning is a dopamine-dependent process in human. [ABSTRACT FROM AUTHOR]

The present project was aimed at investigating how two distinct and important difficulties (coordination difficulty and pronounced dependency on visual feedback) in Parkinson’s disease (PD) affect each other for the coordination between hand transport toward an object and the initiation of finger closure during reach-to-grasp movement. Subjects with PD and age-matched healthy subjects made reach-to-grasp movements to a dowel under conditions in which the target object and/or the hand were either visible or not visible. The involvement of the trunk in task performance was manipulated by positioning the target object within or beyond the participant’s outstretched arm to evaluate the effects of increasing the complexity of intersegmental coordination under different conditions related to the availability of visual feedback in subjects with PD. General kinematic characteristics of the reach-to-grasp movements of the subjects with PD were altered substantially by the removal of target object visibility. Compared with the controls, the subjects with PD considerably lengthened transport time, especially during the aperture closure period, and decreased peak velocity of wrist and trunk movement without target object visibility. Most of these differences were accentuated when the trunk was involved. In contrast, these kinematic parameters did not change depending on the visibility of the hand for both groups. The transport-aperture coordination was assessed in terms of the control law according to which the initiation of aperture closure during the reach occurred when the hand distance-to-target crossed a hand-target distance threshold for grasp initiation that is a function of peak aperture, hand velocity and acceleration, trunk velocity and acceleration, and trunk-target distance at the time of aperture closure initiation. When the hand or the target object was not visible, both groups increased the hand-target distance threshold for grasp initiation compared to its value under full visibility, implying an increase in the hand-target distance-related safety margin for grasping. The increase in the safety margin due to the absence of target object vision or the absence of hand vision was accentuated in the subjects with PD compared to that in the controls. The pronounced increase in the safety margin due to absence of target object vision for the subjects with PD was further accentuated when the trunk was involved compared to when it was not involved. The results imply that individuals with PD have significant limitations regarding neural computations required for efficient utilization of internal representations of target object location and hand motion as well as proprioceptive information about the hand to compensate for the lack of visual information during the performance of complex multisegment movements. [ABSTRACT FROM AUTHOR]

We have previously shown that the distance from the hand to the target at which finger closure is initiated during the reach (aperture closure distance) depends on the amplitude of peak aperture, as well as hand velocity and acceleration. This dependence suggests the existence of a control law according to which a decision to initiate finger closure during the reach is made when the hand distance to target crosses a threshold that is a function of the above movement-related parameters. The present study examined whether the control law is affected by manipulating the visibility of the hand and the target. Young adults made reach-to-grasp movements to a dowel under conditions in which the target or the hand or both were either visible or not visible. Reaching for and grasping a target when the hand and/or target were not visible significantly increased transport time and widened peak aperture. Aperture closure distance was significantly lengthened and wrist peak velocity was decreased only when the target was not visible. Further analysis showed that the control law was significantly different between the visibility-related conditions. When either the hand or target was not visible, the aperture closure distance systematically increased compared to its value for the same amplitude of peak aperture, hand velocity, and acceleration under full visibility. This implies an increase in the distance-related safety margin for grasping when the hand or target is not visible. It has been also found that the same control law can be applied to all conditions, if variables describing hand and target visibility were included in the control law model, as the parameters of the task-related environmental context, in addition to the above movement-related parameters. This suggests that that the CNS utilizes those variables for controlling grasp initiation based on a general control law. [ABSTRACT FROM AUTHOR]

Pointing with an unseen hand to a visual target that disappears prior to movement requires maintaining a memory representation about the target location. The target location can be transformed either into a hand-centered frame of reference during target presentation and remembered under that form, or remembered in terms of retinal and extra-retinal cues and transformed into a body-centered frame of reference before movement initiation. The main goal of the present study was to investigate whether the target is stored in memory in an eye-centered frame, a hand-centered frame or in both frames of reference concomitantly. The task was to locate, memorize, and point to a target in a dark environment. Hand movement was not visible. During the recall delay, participants were asked to move their hand or their eyes in order to disrupt the memory representation of the target. Movement of the eyes during the recall delay was expected to disrupt an eye-centered memory representation whereas movement of the hand was expected to disrupt a hand-centered memory representation by increasing movement variability to the target. Variability of movement amplitude and direction was examined. Results showed that participants were more variable on the directional component of the movement when required to move their hand during recall delay. On the contrary, moving the eyes caused an increase in variability only in the amplitude component of the pointing movement. Taken together, these results suggest that the direction of the movement is coded and remembered in a frame of reference linked to the arm, whereas the amplitude of the movement is remembered in an eye-centered frame of reference. [ABSTRACT FROM AUTHOR]

Previous reports have shown that older adults have difficulties in maintaining allocentric information in memory but not egocentric information. The present study evaluated pointing accuracy in younger and older adults for egocentric and allocentric task. The task was to localize and maintain one, two, or four target locations. Target(s) were presented with or without a surrounding white square in a dimly lit environment. Despite previous postulations, the results of the present study revealed that older adults were able to point to remembered egocentric and allocentric targets as accurately as younger adults regardless of task difficulty. However, older adults took more time pointing to allocentric targets as compared to younger adults. The longer movement time was caused by a lengthening of the deceleration phase, suggesting that during pointing, older adults rely more on visual information surrounding the target than younger adults. [ABSTRACT FROM AUTHOR]

The goal of the present study was to determine whether aging influences aiming performance to a remembered target encoded in an allocentric frame of reference. We presented four targets simultaneously. The targets were then withdrawn from the screen. Following a recall delay, only three of the targets were presented on the screen in the same configuration as before but at a different location from their first presentation. We asked younger ( M =21.9 years) and older participants ( M =73.8 years) to point first to the missing target. Because participants did not know where on the computer screen the targets would be presented at the end of the recall delay, they had no choice but to use an allocentric frame of reference to encode its location when the targets were first presented. The results indicate that older participants were significantly more variable when pointing to the remembered target than their younger counterparts, suggesting a decline of allocentric spatial memory with aging. [ABSTRACT FROM AUTHOR]

ABSTRACT. The issues addressed in 2 experiments in which 10 younger and 10 older adults participated were (a) whether the reten-tion of a target location in memory for motor control purposes would be facilitated by an increase in target presentation time; (b) whether increasing the recall delay since the last exposure to the tar-get would have deleterious effects on aiming accuracy or variability, or both; and (c) whether those effects would be mediated by aging. The results revealed that there is a short-lived (< 1 s) visual representation of target location. In addition, the results suggested that the nature of that representation dictates a movement strategy favoring higher peak movement velocity. None of the effects reported in the present study was affected by age, suggesting that the cod-ing and retrieving processes of target location in memory for motor control purposes are not affected by age. Key words: aging, iconic memory, manual pointing, movement control. [ABSTRACT FROM AUTHOR]

It has been noted that manual aiming error and variability when pointing to remembered targets increase as a function of target eccentricity. In the present study we evaluated which one of three hypotheses (target localization, motor, or movement duration) best explains this 'distance effect'. In experiment 1, older and younger participants aimed with their unseen hand at the remembered location of targets distributed between 129 and 309 mm from the starting base. Target presentation time was of either 50 or 500 ms and aiming movements could be initiated following either a 100- or a 10,000-ms recall delay. Participants had either no constraints concerning movement time or were asked to reach the near target in a longer movement time than the farther targets. The results revealed a significant distance effect when no time constraints were imposed but showed a significantly reversed distance effect when the instructions were to reach the near targets in a longer movement time than the far targets. The same results were obtained regardless of target presentation time, recall delay, or age of the participants. These results supported a movement duration interpretation of the distance effect. In experiment 2, a distance effect was replicated when pointing with one's unseen hand toward a remembered target but did not take place when pointing to visible targets. Taken together these results suggest that prolonged movement execution interferes with the stored egocentric target representation. [ABSTRACT FROM AUTHOR]