Externally guided control of static grip forces by visual feedback-age and task effects in 3-6-year old children and in adults

Tongue Strength in Children With and Without Speech Sound Disorders

Purpose The purpose of this cross-sectional investigation was to expand the comparative database of pediatric tongue strength for children and adolescents with typical development, ages 3-17 years, and compare tongue strength among children with typical development, speech sound delay/disorders (SD), and motor speech disorders (MSDs). Method Tongue strength was measured using the Iowa Oral Performance Instrument in a total of 286 children and adolescents, 228 with typical development, 16 with SD, and 42 with MSDs, including classic galactosemia, a known risk factor for MSD ( n = 33) and idiopathic MSD ( n = 9). Results For all groups, tongue strength increased rapidly from 3 to 6.5 years of age and then continued to increase with age at a slower rate until 17 years of age. Children with SD's tongue strength did not differ from their typically developing (TD) peers. Children and adolescents with MSDs had decreased tongue strength compared to children with typical development or SD. Tongue strength was not related to severity of speech sound disorders in SD or MSD. Conclusion Weak tongue strength does not appear to contribute to speech errors in children with speech sound delays but does appear to be related to speech sound disorders that are neurologic in origin (developmental MSD).

Improvements in force variability and structure from vision- to memory-guided submaximal isometric knee extension in subacute stroke

We examined changes in variability, accuracy, frequency composition, and temporal regularity of force signal from vision-guided to memory-guided force-matching tasks in 17 subacute stroke and 17 age-matched healthy subjects. Subjects performed a unilateral isometric knee extension at 10, 30, and 50% of peak torque [maximum voluntary contraction (MVC)] for 10 s (3 trials each). Visual feedback was removed at the 5-s mark in the first two trials (feedback withdrawal), and 30 s after the second trial the subjects were asked to produce the target force without visual feedback (force recall). The coefficient of variation and constant error were used to quantify force variability and accuracy. Force structure was assessed by the median frequency, relative spectral power in the 0-3-Hz band, and sample entropy of the force signal. At 10% MVC, the force signal in subacute stroke subjects became steadier, more broadband, and temporally more irregular after the withdrawal of visual feedback, with progressively larger error at higher contraction levels. Also, the lack of modulation in the spectral frequency at higher force levels with visual feedback persisted in both the withdrawal and recall conditions. In terms of changes from the visual feedback condition, the feedback withdrawal produced a greater difference between the paretic, nonparetic, and control legs than the force recall. The overall results suggest improvements in force variability and structure from vision- to memory-guided force control in subacute stroke despite decreased accuracy. Different sensory-motor memory retrieval mechanisms seem to be involved in the feedback withdrawal and force recall conditions, which deserves further study. NEW & NOTEWORTHY We demonstrate that in the subacute phase of stroke, force signals during a low-level isometric knee extension become steadier, more broadband in spectral power, and more complex after removal of visual feedback. Larger force errors are produced when recalling target forces than immediately after withdrawing visual feedback. Although visual feedback offers better accuracy, it worsens force variability and structure in subacute stroke. The feedback withdrawal and force recall conditions seem to involve different memory retrieval mechanisms.

Using Virtual Reality to Transfer Motor Skill Knowledge from One Hand to Another

As far as acquiring motor skills is concerned, training by voluntary physical movement is superior to all other forms of training (e.g. training by observation or passive movement of trainee's hands by a robotic device). This obviously presents a major challenge in the rehabilitation of a paretic limb since voluntary control of physical movement is limited. Here, we describe a novel training scheme we have developed that has the potential to circumvent this major challenge. We exploited the voluntary control of one hand and provided real-time movement-based manipulated sensory feedback as if the other hand is moving. Visual manipulation through virtual reality (VR) was combined with a device that yokes left-hand fingers to passively follow right-hand voluntary finger movements. In healthy subjects, we demonstrate enhanced within-session performance gains of a limb in the absence of voluntary physical training. Results in healthy subjects suggest that training with the unique VR setup might also be beneficial for patients with upper limb hemiparesis by exploiting the voluntary control of their healthy hand to improve rehabilitation of their affected hand.

Improving manual skills in persons with disabilities (PWD) through a multimodal assistance system

In this research work, we present a Multimodal Guidance System (MGS) whose aim is to provide dynamic assistance to persons with disabilities (PWD) while performing manual activities such as drawing, coloring in and foam-cutting tasks. The MGS provides robotic assistance in the execution of 2D tasks through haptic and sound interactions. Haptic technology provides the virtual path of 2D shapes through the point-based approach, while sound technology provides audio feedback inputs related to the hand's velocity while sketching and filling or cutting operations. By combining this Multimodal System with the haptic assistance, we have created a new approach with possible applications to such diverse fields as physical rehabilitation, scientific investigation of sensorimotor learning and assessment of hand movements in PWD. The MGS has been tested by people with specific disorders affecting coordination, such as Down syndrome and developmental disabilities, under the supervision of their teachers and care assistants inside their learning environment. A Graphic User Interface has been designed for teachers and care assistants in order to provide training during the test sessions. Our results provide conclusive evidence that the effect of using the MGS increases the accuracy in the tasks operations.

IMPLICATIONS FOR REHABILITATION

The Multimodal Guidance System (MGS) is an interface that offers haptic and sound feedback while performing manual tasks. Several studies demonstrated that the haptic guidance systems can help people in recovering cognitive function at different levels of complexity and impairment. The applications supported by our device could also have an important role in supporting physical therapist and cognitive psychologist in helping patients to recover motor and visuo-spatial abilities.

Using the "visual target grip test" to identify sincerity of effort during grip strength testing

We devised a sincerity of effort assessment based on "tricking" a person into exerting maximal effort by providing incorrect visual feedback. The assessment involves deriving a target line from nonvisual peak gripping force, instructing participants to reach it with each grip repetition, and then secretly changing its position, which requires doubling the force necessary to reach it. Accordingly, participants are tricked into exerting more force than intended to reach the deceptive target line. We examined the validity of this test by comparing force values between "trick" and "non-trick" trials in 30 healthy participants. The study design used was a prospective cohort. Providing incorrect visual feedback caused significantly greater increases in force during submaximal effort (69%) than during maximal effort (28%). This test effectively detected submaximal effort (sensitivity=0.83 and specificity=0.93). Although this test is not safe for patients during initial therapy, it may be appropriate for patients who can safely exert maximal grip force.

LEVEL OF EVIDENCE

Not applicable.

Low-frequency fluctuation in continuous real-time feedback of finger force: a new paradigm for sustained attention

OBJECTIVE

Behavioral studies have suggested a low-frequency (0.05 Hz) fluctuation of sustained attention on the basis of the intra-individual variability of reaction-time. Conventional task designs for functional magnetic resonance imaging (fMRI) studies are not appropriate for frequency analysis. The present study aimed to propose a new paradigm, real-time finger force feedback (RT-FFF), to study the brain mechanisms of sustained attention and neurofeedback.

METHODS

We compared the low-frequency fluctuations in both behavioral and fMRI data from 38 healthy adults (19 males; mean age, 22.3 years). Two fMRI sessions, in RT-FFF and sham finger force feedback (S-FFF) states, were acquired (TR 2 s, Siemens Trio 3-Tesla scanner, 8 min each, counter-balanced). Behavioral data of finger force were obtained simultaneously at a sampling rate of 250 Hz.

RESULTS

Frequency analysis of the behavioral data showed lower amplitude in the low-frequency band (0.004-0.104 Hz) but higher amplitude in the high-frequency band (27.02-125 Hz) in the RT-FFF than the S-FFF states. The mean finger force was not significantly different between the two states. fMRI data analysis showed higher fractional amplitude of low-frequency fluctuation (fALFF) in the S-FFF than in the RT-FFF state in the visual cortex, but higher fALFF in RT-FFF than S-FFF in the middle frontal gyrus, the superior frontal gyrus, and the default mode network.

CONCLUSION

The behavioral results suggest that the proposed paradigm may provide a new approach to studies of sustained attention. The fMRI results suggest that a distributed network including visual, motor, attentional, and default mode networks may be involved in sustained attention and/or real-time feedback. This paradigm may be helpful for future studies on deficits of attention, such as attention deficit hyperactivity disorder and mild traumatic brain injury.

Verbal Regulation of Grip Force in Preschoolers

The purpose of this study was to clarify the developmental processes in verbal regulation by preschool children. Participants were 152 typically developing children (74 boys, 78 girls) between 4 and 6 years of age ( M = 5.3, SD =.8), and 30 healthy adults (15 men, 15 women) between 19 and 26 years of age ( M = 20.8, SD = 1.4). In Exp. 1, the task was to regulate grip force based on quantitative instruction which implies using a scale for regulation. Participants were required to produce a half-grip force of the maximum (Task 1). In Exp. 2, the task was grip-force regulation based on nonquantitative instruction. The participants were asked to respond with a slightly weaker grip force than the maximum (Task 2) and then a further weaker grip force (Task 3) than that used on Task 2. The regulation rates produced the extent of regulation and suggest regulation by quantitative instruction may develop earlier than by nonquantitative instruction. Also, precise grip-force regulation based on the semantic aspect of instruction may be difficult for young children. The developmental changes in the rate of performance especially observed in children of 4 to 6 years indicate that the tendency to use too much grip force disappears during this preschool period. In addition, too little grip force in regulation may reflect the developmental process toward fine grasping movements.

Basic motor capacity in relation to object manipulation and general manual ability in young children with spastic cerebral palsy

OBJECTIVE

Limited resources in terms of elementary functions may be a limiting factor for functional activities. The objective of the study was to examine basic hand motor capacities in young children with bilateral spastic cerebral palsy (BSCP) and to compare with deficits in functional activities.

METHOD

Eighty-eight children with BSCP, 3-6 years of age, manipulated a grip object (200g) equipped with a uniaxial force sensor. Basic motor capacity was assessed based upon (1) maximal grip strength and (2) production of fast repetitive grip force changes (FFC) while holding the object on the table. Subjects' performance on this task was compared to the grip force amplitude and force rate assessed while the subject was lifting the same object. Results were compared between different degrees of manual ability according to the Manual Ability Classification System (MACS).

RESULTS

In children with BSCP, even in high-functioning children with MACS 1, fast grip force changes and grip strength were 2 SDs and more below the mean of controls. Differences increased from MACS 2 to 4 but not between MACS 1 and 2. During lifting children with BSCP used considerable proportions of their maximum grip strength (40-90%) and of their grip force rates during 70% vs. 86%. In some children with low manual abilities (MACS 3/4), grip force rates during lifting were higher than during FFC.

CONCLUSION

In children with BSCP, basic motor capacity may influence manual ability, particularly in children with MACS 3 and 4. In some of these children, the underlying processes during lifting may also differ qualitatively.

Adolescent development of motor imagery in a visually guided pointing task

The development of action representation during adolescence was investigated using a visually guided pointing motor task (VGPT) to test motor imagery. Forty adolescents (24 males; mean age 13.1 years) and 33 adults (15 males; mean age 27.5 years) were instructed to both execute and imagine hand movements from a starting point to a target of varying size. Reaction time (RT) was measured for both Execution (E) and Imagery (I) conditions. There is typically a close association between time taken to execute and image actions in adults because action execution and action simulation rely on overlapping neural circuitry. Further, representations of actions are governed by the same speed-accuracy trade-off as real actions, as expressed by Fitts' Law. In the current study, performance on the VGPT in both adolescents and adults conformed to Fitts' Law in E and I conditions. However, the strength of association between E and I significantly increased with age, reflecting a refinement in action representation between adolescence and adulthood.

Task-dependent organization of pinch grip forces

The organization of thumb and index finger forces in a pinch formation was investigated under conditions where kinetic constraints on interdigit force coupling were removed. Two visually guided isometric force tasks at submaximal levels were used to characterize the spatial and temporal aspects of interdigit force coupling. Task 1 provided an initial characterization of interdigit force coordination when the force relationship between the digits was not specified. Task 2 probed the extent to which a preferred coordination of the thumb and index finger could be decoupled, both temporally and with respect to force magnitude, by specifying the coordination between the digit forces. Digit forces were measured using a pinch apparatus that was instrumented to record the magnitude and direction of the thumb (F(t)) and index finger (F(i)) forces, independently. Two apparatus conditions allowed further examination of interdigit force coordination when the relationship between digit forces was mechanically constrained (pivot condition), and when the relationship between digit forces was not constrained, allowing the neuromotor system to select a preferred pattern of interdigit coordination (fixed condition). Sixteen right-handed adults exerted a pinch force against the apparatus to match a single-cycle sine wave that varied between 15 and 35% of each participant's maximal voluntary pinch force. The target was presented with positive or negative target sense, to vary the order of force level and direction of force change across the trials. When the mechanical constraints allowed selection of a preferred coordination pattern, F(t) = F(i) was a robust result. In contrast, when the coordination between the digit forces was specified by the requirement to simultaneously produce and control independent thumb and index finger forces while acting on a stable object, subjects were able to produce forces that markedly deviated from the F(t) = F(i) coordination. The organization of pinch is characterized by a preferred, tight coupling of digit forces, which can be modified based on task demands.

Electrophysiological and hemodynamic evidence for late maturation of hand power grip and force control under visual feedback

Several human imaging studies have described the neural network involved in power grip under visual control and the subset of cortical areas within this network that are sensitive to force modulation. As there is behavioral evidence for late maturation in even simple hand motor tasks involving visual feedback, we aimed at identifying the neural correlates of these developmental changes. Subjects from three developmental age groups (9-11, 15-17, and adults) performed the same power grip task in both a functional magnetic resonance imaging and an event-related potential (ERP) session. Trials started with a visual target indicating whether to squeeze at 20%, 40%, or 75% of their maximum and online visual feedback on the actual amount of force was provided. Longer reaction times and more shallow slopes of the force curve characterized the behavior of the younger age groups, especially the children. Both neurophysiological methods detected both general as well as force modulation-specific maturational changes. General development was characterized by decreasing ERP amplitudes and increasing deactivation of an extended network, closely resembling the so-called "default" network. The most pronounced developmental changes specific for force control were observed in an ERP component and brain regions involved in feedback processing. In contrast to adult subjects, we found evidence for a stronger dependency on visual feedback information in the younger age groups. Our results also suggest that the ability to deactivate task-irrelevant networks might be a late developmental achievement.

Development of action representation during adolescence

During adolescence the body undergoes many physical changes. These changes necessitate an updating of internal models of action. Here, we tested the hypothesis that internal models undergo refinement between adolescence and adulthood. We investigated the chronometry of executed and imagined hand actions, which relies on internal models, in 40 adolescents (24 males; mean age 13.1 years) and 33 adults (15 males; mean age 27.5 years). In two different motor imagery tasks, the time it took each participant to execute a hand movement was compared with the time it took them to imagine making that movement. For all participants, movement execution time significantly correlated with movement imagery time. However, there was a significant increase in the execution-imagery time correlation between adolescence and adulthood. Cognitive-motor efficiency per se did not change as indexed by both similar execution and imagery times on both tasks for the adolescents and adults. That it was only the correlation between imagined and executed actions that changed with age suggests that the developmental change was specific to generating accurate motor images and not a result of general cognitive improvement with age. The results support the notion that aspects of internal models are refined during adolescence. We suggest that this refinement may be facilitated by the development of parietal cortex during adolescence.

Age-related differences in inter-digit coupling during finger pinching

The present study was designed to examine the finger-pinch force control, digit force sharing and digit coupling relations of 13 young and 14 older adults. Subjects performed four isometric tri-digit finger-pinch force production conditions reflecting all combinations of mean force level (20 and 40% MVC) and target shape (constant and sinusoidal). Older adults had significantly reduced force control, as indicated by their greater levels of absolute and relative force variability and targeting error than young adults. The age-related loss of relative force control was more pronounced at low (20% MVC) than high (40% MVC) forces, and to a lesser extent, in sinusoidal than constant force conditions. Older adults had significantly greater peak and proportional power below 1.5 Hz than young adults, with this especially pronounced in constant force conditions. Digit force sharing results indicated that the index finger's contribution to total force was increased and the middle finger's contribution reduced in older than young adults. The results of the cross-correlation analyses revealed that older subjects had a significantly reduced level of coupling between the middle finger and the target force, thumb force and EMG signals, with longer time lags in comparison to young adults. These differences in force sharing and middle finger force coupling were more pronounced in sinusoidal than constant force conditions. Overall, these results suggest that the older adults' reduced force control reflected age-related differences in the sharing and coupling of the finger forces. The results also highlighted that tasks of this nature display a degree of task-dependency, with these overall differences in digit force output and coupling not consistently observed across all force conditions.

Power and precision grip force control in three-to-five-year-old children: velocity control precedes amplitude control in development

The aim of this study was to examine the development of underlying motor control strategies in young children by characterizing the changes in performance of a visually guided force regulation task using two different grip formations; a whole-hand power grip (developmentally easier) and a thumb-index finger precision grip (developmentally more advanced). Typically developing preschool children (n=50, 3.0-5.5 years) used precision and power grips to perform a ramp and hold task with their dominant and non-dominant hands. Participants performed five trials with each hand and grip holding the force at 30% of their maximum volitional contraction for 3 s. The data were examined for both age-related and performance-related changes in motor performance. Across ages, children increased in strength, decreased in initial overshoot of the target force level, and decreased in rate of force release. Results of a cluster analysis suggest non-linear changes in the development of force control in preschool children, with a plateau in (or maturation of) velocity measures (rate of force increase and force decrease) earlier than in amplitude-related measures (initial force overshoot and force variability).

Children with spastic hemiplegia are equally able as controls in maintaining a precise percentage of maximum force without visually monitoring their performance

In this study the hypothesis was tested that children with spastic hemiplegia rely more on externally guided visual feedback when trying to keep force constant with their affected hand (AH) as compared to their non-affected hand (NAH) and as compared to controls. An isometric force task in which a cursor had to be moved to a visually specified target that disappeared half way the task, was performed by 19 children with cerebral palsy (CP), spastic hemiplegia, aged between 5 and 16 years and an aged matched control group. It was found that the absolute deterioration of performance after withdrawal of target visualization did differ between AH, NAH and controls. The absolute error was smaller and the variability was larger in the hemiplegic hand. However, the normalized force error and co-efficient of variation increased similarly between groups. Furthermore, power spectrum density analysis of the force signal showed that both hands in both groups had a similar loss in the energy in the 2-3 Hz range when target visualization was removed. These results suggest that CP children are equally able to produce stable force without visually monitoring their performance than children without CP, provided they are allowed to operate within their own force range.

Changes in the structure of children's isometric force variability with practice

This study examined the effect of age and practice on the structure of children's force variability to test the information processing hypothesis that a reduction of sensorimotor system noise accounts in large part for age-related reductions in perceptual-motor performance variability. In the study, 6-year-olds, 10-year-olds, and young adults practiced on 5 consecutive days (15 trials/day), maintaining for 15-s trials a constant level of force (5 or 25% of maximum voluntary contraction) against an object using a pinch grip (thumb and index finger). With increasing age, the amount of force error and variability decreased, but the sequential structure of variability increased in irregularity. With practice, children reduced the amount of variability by changing the structure of the force output so as to be more similar to that of their older counterparts. The findings provide further evidence that practice-driven changes in the structure of force output, rather than a decline in the amount of white noise, largely account for age-related reductions in the amount of force variability.

Development of isometric force and force control in children

Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that optimal performance (in terms of force variability control) closely matches the maturation of the corticospinal tract up to age 10. It was found that maximum voluntary contraction (MVC) matured over the full range of the examined age groups. In contrast, the coefficient of variation of force showed maturation mainly up to the age of 9-10, as hypothesised. Gender differences were found for MVC but not for the other force control parameters. Power spectral density analysis revealed developmental differences in the lower (1-6 and 7-12 Hz) and higher frequencies bands (13-18 and 19-24 Hz). In the lowest frequency range the amount of energy decreased with age, presumably because young children (5-8 years of age) rely more heavily on control from proprioceptive and visual feedback. It is argued that with increasing neural maturation the control processes become more dependent upon internal representation manifested by feed forward control that starts to substitute feedback-based control.

Children's coordination of force output in a pinch grip task

This study examined the role of sensorimotor system noise in the organization of the force output of the thumb and index finger and the coordination between the two digits in an isometric pinch grip force task as a function of age (6, 8, 10, 18-22 years), feedback condition (with and without visual feedback information), and force level (5, 15, 25, and 35% of maximal voluntary force. With increases in age under the visual feedback conditions, the signal-to-noise ratio increased, the sequential structure of the force output signals became more irregular, the degree of coherence between the digits at higher force levels was enhanced, and the digits exhibited a greater degree of coherence across the higher frequencies of the power spectrum at all force levels. However, these age differences were either minimized or eliminated under conditions without feedback. These findings show that the age-related performance differences in grip force variability are primarily due to more effective use of visual information rather than age differences in intrinsic sensorimotor noise.

Influence of the age on self regulation of static grip forces from perceived exertion values

The investigation of self-regulation of grip force provides indirect cues about the developmental neurobiology of the subject. The aim of this study was to examine the ability of subjects of different ages to produce different forces based on their perceived exertion during a grip force task by using a test and a randomised re-test procedure. Eighteen young children (aged 6.5 years), 18 adolescents (13.5 years) and 18 adults (28.5 years) performed a graded hand grip strength test (GST) at four intensities. Perceived exertion (RPE-C) was recorded at the end of each load level. Then, subjects were scheduled for a randomised grip strength test performed in the same experimental conditions than GST. Statistical analysis revealed no significant effect in grip strength for test in the three groups. However, a significant main effect for intensities was obtained in the three groups (P < 0.0001). Significant correlations were observed between GST and RPE-C (r(2) = 0.62, P < 0.0001; r(2) = 0.53, P < 0.0001; r(2) = 0.51, P < 0.0001), in the children, adolescent and adult groups, respectively. However at low grip force intensities, it appears that children have some difficulties to rate their perceived exertion. The results of this study suggest that the neurodevelopmental level of 6-year-old children do not affect the ability to produce reliably moderate to intense forces from perceived exertion during a grip force task.

Clinical evaluator reliability for quantitative and manual muscle testing measures of strength in children

Measurements of muscle strength in clinical trials of Duchenne muscular dystrophy have relied heavily on manual muscle testing (MMT). The high level of intra- and interrater variability of MMT compromises clinical study results. We compared the reliability of 12 clinical evaluators in performing MMT and quantitative muscle testing (QMT) on 12 children with muscular dystrophy. QMT was reliable, with an interclass correlation coefficient (ICC) of >0.9 for biceps and grip strength, and >0.8 for quadriceps strength. Training of both subjects and evaluators was easily accomplished. MMT was not as reliable, and required repeated training of evaluators to bring all groups to an ICC >0.75 for shoulder abduction, elbow and hip flexion, knee extension, and ankle dorsiflexion. We conclude that QMT shows greater reliability and is easier to implement than MMT. Consequently, QMT will be a superior measure of strength for use in pediatric, neuromuscular, multicenter clinical trials.

Development of externally guided grip force modulation in man

We examined the development of externally guided changes of grip force with respect to force rate and direction of force change. Sixty-nine children, 3-6 years of age, and 17 adults produced increasing or decreasing isometric forces on a small cylindrical sensor using a pinch grip with visual feedback. Force changes were instructed with a visual tracking task. Ramp-like paradigms with both force increase and force decrease and two different target force rates were used (0.5 N/s, 1.25 N/s). Precision of force tracking showed clear age effects and was influenced by the required force rates and directions of force change. In adults, tracking errors were much more dependent on target force rate and direction than in children. Up to four years of age, the children tended to overshoot the target force change in a 'jump and wait' manner in all conditions except for fast target force decreases. Older children tended to overshoot only in the condition with slow target force decrease. Adults showed close undershooting in all conditions when following the target. Adults used either a continuous 'following' strategy or a 'see and catch-up' strategy. The distinct effects on tracking errors suggest an age-related change of strategies from a feedforward strategy with intermittent use of sensorimotor feedback towards a fairly parallel and well-integrated feedback and feedforward processing. A critical age appears to be around five to six years. We suggest that these age effects may reflect distinct developmental velocities of neuronal subpopulations of the cortex and of the cerebello-cortical connections.