SEARCH · PubMed Health

Results for “reaching”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources

PubMed2002

Sequential control signals determine arm and trunk contributions to hand transport during reaching in humans.

When reaching towards objects placed outside the arm workspace, the trunk assumes an active role in transport of the hand by contributing to the extent of movement while simultaneously maintaining the direction of reach. We investigated the spatial-temporal aspects of the integration of the trunk motion into reaching. Specifically, we tested the hypothesis that the efficiency ('gain') of the arm-trunk co-ordination determining the contribution of the trunk to the extent of hand movement may vary substantially with the phase of reaching. Sitting subjects made fast pointing movements towards ipsi- and a contralateral targets placed beyond the reach of the right arm so that a forward trunk motion was required to assist in transporting the hand to the target. Sight of the arm and target was blocked before the movement onset. In randomly selected trials, the trunk motion was unexpectedly prevented by an electromagnet. Subjects were instructed to make stereotypical movements whether or not the trunk was arrested. In non-perturbed trials, most subjects began to move the hand and trunk simultaneously. In trunk-blocked trials, it was impossible for the hand to cover the whole pointing distance but the hand trajectory and velocity profile initially matched those from the trials in which the trunk motion was free, approximately until the hand reached its peak velocity. The arm inter-joint co-ordination substantially changed in response to the trunk arrest at a minimal latency of 40 ms after the perturbation onset. The results suggest that when the trunk was free, the influence of the trunk motion on the hand trajectory and velocity profile was initially neutralized by appropriate changes in the arm joint angles. Only after the hand had reached its peak velocity did the trunk contribute to the extent of pointing. Previous studies suggested that the central commands underlying the transport component of arm movements are completed when the hand reaches peak velocity. These studies, together with the present finding that the trunk only begins to contribute to the hand displacement at peak hand velocity, imply that the central commands that determine the contributions of the arm and the trunk to the transport of the hand are generated sequentially, even though the arm and trunk move in parallel.

Adult↗

PubMed1989

Inferior parietal lobule neurones related to eye and hand reach movements in rhesus monkey.

Analysis was made on neuronal responses of the inferior parietal lobule to visual, jump, or 'reach' behavioral paradigm in 2 awake, trained rhesus monkeys. Preconditioning and antidromic electrical stimulation of medial and oral pulvinar LP nuclei and the arcuate gyrus aided the study. The results reveal two reach cell categories: one with no definable visual sensitivity (NVHRN) and one with visual receptive field responsiveness (VHRN). The VHRN reach cell firing is characterized by an early component. As the latter was observed only when the monkey reached loci inside but not outside of the cell-receptive field, it was equated with the cell visual receptive field response. This component could be voided by preconditioning stimulation of medial pulvinar or LP, the latencies of the VHRN responses becoming longer and comparable to NVHRN. If the consequences of reaching were nulled in any of a few different ways, such as preventing the monkey from reaching, disenabling the panel key, or denying the reward, a reach cell biphasic firing response showed no change in the first burst, but the second burst was absent, suggesting the latter's relation to satiation. If a jump cell's visual responses enhanced by the 'jump' paradigm were negated by preconditioning stimulation, the saccadic eye movement that otherwise followed the enhanced signals was replaced by another saccade, different in direction and amplitude, as if of other frames of reference. It seems, therefore, that the inferior parietal lobe system subserves in two types of reach behaviour: one with and one without visual guidance, playing perhaps a role in selecting strategies such as the dynamic option to do away with the visual guidance, if circumstances demand.

Animals↗

PubMedDate not supplied

Hard-to-reach providers: targeted HIV education by the national AIDS education and training centers.

A national system of AIDS Education and Training Centers (AETCs) has received federal funding since 1987 to provide education to health care personnel (HCP) about HIV infection. The purpose of this study is to describe how AETC program personnel define and recognize HCP who are hard to reach and educate about HIV and to clarify the issues that make providers hard to reach. Twenty-three semistructured telephone interviews were used to collect data from AETC faculty and staff. Respondents were asked to identify the types of HCP who are hard to reach and to discuss why they are hard to reach. Themes identified to establish which HCP are hard to reach include specific professional groups (especially physicians and dentists) as well as providers who treated less than 10 HIV-infected clients and some HIV-expert clinicians. Themes identified to establish why they are hard to reach include convenience, isolation, and attitudes. Analysis posits that hard-to-reach HCP fall into identifiable categories: "already know the information," "don't know they don't know the information," "don't think they need to know the information," or "don't want to know the information." Respondents also identified innovative ways to approach hard-to-reach providers.

Area Health Education Centers↗

PubMed2006

Relationships between sensorimotor impairments and reaching deficits in acute hemiparesis.

OBJECTIVE: To determine the relationships between sensorimotor impairments and upper extremity reaching performance during the acute phase of stroke and to determine which, if any, measures of sensorimotor impairment can predict variance in reaching performance during this phase. METHODS: Sensorimotor impairments of upper extremity (UE) strength, active range of motion, isolated movement control, light touch sensation, joint position sense, spasticity, and shoulder pain were evaluated in a group of 46 individuals with acute hemiparesis (mean time since insult = 9.2 days). Subjects performed a reaching task to a target placed on their affected side. Three-dimensional kinematic analyses were used to assess reaching speed, accuracy, and efficiency. Forward stepwise multiple linear regression analyses were used to determine which impairment was the best predictor of variance in reaching performance. RESULTS: Measures of UE strength predicted the largest proportion of variance in the speed, accuracy, and efficiency of forward reaching. Isolated movement control, somatosensory deficits, and elbow spasticity predicted smaller amounts of variance in reaching performance. CONCLUSIONS: The authors' data show that deficits in strength appear to be the most influential sensorimotor impairment associated with limited reaching performance in subjects with acute hemiparesis.

Adult↗

PubMed2003

Kinematic quality of reaching movements in preterm infants.

Many preterm infants may experience so-called minor developmental disorders; however, in general, the problems in motor behavior are not detected until school age. To introduce therapies aimed at the prevention of these problems, we need to increase our knowledge of motor function and dysfunction at early age. The present study focused on the organization of reaching movements in full-term and preterm infants without cerebral palsy. The reaching behavior of premature infants (n = 63) was assessed longitudinally at the corrected ages of 4 and 6 mo. Clinical assessments were made at 6 and 12 mo of age. On the basis of the infant's morbidity during the early stay in the neonatal intensive care unit, the preterm infants were allocated into a high-risk and a low-risk group. Results from a previous study in full-term infants (n = 13) were included. Kinematics of reaching movements in supine position were measured, and the analysis focused on movement velocity and movement units. A compound parameter of kinematic variables was created, reflecting the quality of reaching movements. The present study showed that at the age of 4 mo, low-risk preterm infants showed more often optimal reaching behavior than full-term and preterm high-risk infants. This better reaching performance was related to a better general motor and behavioral development during the first year of life. At the age of 6 mo, the advantage of the low-risk group in reaching behavior had disappeared and a disadvantage in the form of nonoptimal reaching behavior of the high-risk group emerged.

Arm↗

PubMed1999

Criterion-related validity of sit-and-reach tests in university men in Hong Kong.

To examine the criterion-related validity of traditional, modified, and YMCA sit-and-reach tests and the relationships of these with abdominal muscular strength and endurance measured by the sit-up test, 52 university men of mean age 20.7 yr. were administered two trials of six measurements in counterbalanced order, including traditional, modified, and YMCA sit-and-reach tests, passive straight-leg raise, low-back flexibility evaluation, and 1-min. sit-up test. Pearson product-moment correlations were significant (p < .05) for traditional and modified sit-and-reach tests with hamstrings' flexibility (rs = .71 and .77, respectively). Also, the YMCA sit-and-reach test was significantly associated with hamstrings' flexibility (r = .64) and low-back flexibility (r = .47). Stepwise multiple regression indicated hamstrings' flexibility was the only significant predictor of traditional and modified sit-and-reach tests, explaining the variances of 59.1% and 49.8%, respectively. However, both hamstring and low-back flexibility were significant predictors for the YMCA sit-and-reach test, which in total accounted for 52.2% of explained variance. Traditional and modified sit-and-reach tests are valid in assessing hamstrings' flexibility only, whereas the YMCA sit-and-reach test is valid for measuring both the hamstring and low-back flexibility.

Abdominal Muscles↗

PubMed1999

Cognitive influence on motor control in reaching.

The purpose of this study was to assess the effects of objects with different attributes on motor control in the act of reaching for them. Much about reaching has been studied from the point of view of spatial relations between objects and subjects, and kinematic approaches have played an important role in this field. Recently, some researchers have proposed that factors other than spatial relations characterize reaching. Therefore, we focused on reaching for an empty glass (empty condition) and a water-filled glass (filled condition) where the positions of the glasses were the same to examine the importance of the objects when reaching for them. Eight young adults participated. We translated the position of the index finger into X-Y-Z coordinate values and examined movement time, length of trajectory, and velocity between the empty and filled conditions. It took longer to reach for an empty than a filled glass, and the filled condition showed a longer trajectory and slower velocity than the empty condition. This indicated that objects with different attributes influenced the reaching and that the role of cognition of attributes is important in the act of reaching.

Adult↗

PubMed2004

Distortions of distance and shape are not produced by a single continuous transformation of reach space.

We investigated whether distortions of perceived distance and shape could be captured by a single continuous one-to-one transformation of the underlying space. In Experiment 1, the participants reached to touch points around the perimeter of spherical targets viewed at five different distances, to yield simultaneous measures of perceived distance and shape. Different participants reached while using dynamic monocular, static binocular, or dynamic binocular vision. Thin plate spline (TPS) analysis was applied so as to transform a Cartesian grid in such a way as to carry the original target points to the mean reach locations. In all cases, discontinuities appeared in the transformed grid from folding of the space. In Experiment 2, the participants reached to points that lay at the same locus in reach space, but on different portions of the visible target spheres (e.g., front vs. side). The participants reached to different locations when the points were different with respect to shape (e.g., front vs. side) but reached to the same locations when the points were the same with respect to shape (left vs. right side). TPS analysis revealed discontinuities from holes torn in the underlying space. The results show that perceived distance and perceived shape entail different distortions and cannot be captured by a single continuous transformation of reach space.

Adult↗

PubMed2002

Efficacy of the Star Excursion Balance Tests in Detecting Reach Deficits in Subjects With Chronic Ankle Instability.

OBJECTIVE: Chronic instability after lateral ankle sprain has been shown to cause balance deficits during quiet standing. Although static balance assessment in those with ankle instability has been thoroughly examined in the literature, few researchers have studied performance on more dynamic tasks. Our purpose was to determine if the Star Excursion Balance Tests (SEBTs), lower extremity reach tests, can detect deficits in subjects with chronic ankle instability. DESIGN AND SETTING: We performed all testing in a university athletic training facility. We tested lower extremity reach using the SEBTs, which incorporates single-leg stance with maximal reach of the contralateral leg. SUBJECTS: Twenty subjects with unilateral, chronic ankle instability (age = 19.8 +/- 1.4 years, height = 176.8 +/- 4.5 cm, mass = 82.9 +/- 21.2 kg) and 20 uninjured subjects matched by sex, sport, and position (age = 20.2 +/- 1.4 years, height = 178.7 +/- 4.1 cm, mass = 82.7 +/- 19.9 kg). MEASUREMENTS: We measured the reach distances in centimeters (cm) and averaged 3 reaches in each of the 8 directions while the subjects stood on each leg for data analysis. RESULTS: The group with chronic ankle instability demonstrated significantly decreased reach while standing on the injured limb compared with the matched limb of the uninjured group (78.6 cm versus 82.8 cm). Additionally, subjects with chronic ankle instability reached significantly less when standing on their injured limbs as compared with their uninjured limbs (78.6 cm versus 81.2 cm). CONCLUSIONS: The SEBTs appear to be an effective means for determining reach deficits both between and within subjects with unilateral chronic ankle instability.

Journal Article↗

PubMed1993

The transition to reaching: mapping intention and intrinsic dynamics.

The onset of directed reaching demarks the emergence of a qualitatively new skill. In this study we asked how intentional reaching arises from infants' ongoing, intrinsic movement dynamics, and how first reaches become successively adapted to the task. We observed 4 infants weekly in a standard reaching task and identified the week of first arm-extended reach, and the 2 weeks before and after onset. The infants first reached at ages ranging from 12 to 22 weeks, and they used different strategies to get the toy. 2 infants, whose spontaneous movements were large and vigorous, damped down their fast, forceful movements. The 2 quieter infants generated faster and more energetic movements to lift their arms. The infants modulated reaches in task-appropriate ways in the weeks following onset. Reaching emerges when infants can intentionally adjust the force and compliance of the arm, often using muscle coactivation. These results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns. Rather, these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.

Arm↗

PubMedDate not supplied

Functional reach and single leg stance in patients with peripheral vestibular disorders.

The purpose of this study was to compare functional reach distance and right single leg stance time in patients who had peripheral vestibular disease. Twenty-eight patients (15 female, 13 male) between the ages of 35 and 84 were asked to perform 3 trials each of functional reach (FR) and right single leg stance (SLS). SLS times were measured by a Kistler static force platform on line with a Caspar personal computer. FR distance was measured by using a free-standing 147-cm rule. In addition, each subject filled out the Dizziness Handicap Inventory (DHI). Trials were randomized to prevent fatigue or practice effects. A Pearson product-moment correlation was performed between FR and SLS (r = 0.59, P = 0.001). Post hoc analyses of the first, the best, and the average scores highlighted the importance of using means for comparison in a population as variable as the vestibularly impaired. Post hoc analyses showed no correlation between the DHI score and either functional reach distance or single leg stance time. However, when the subjects were divided into groups based on DHI score (group 1 with DHI < or = 49/100, group 2 with DHI > or = 50/100) and a pooled two-sample t-test was performed, a significant difference (P = 0.05) was found in functional reach distance; the subjects who reported less perception of handicap reached farther than those who reported more perception of handicap. No difference was found between the two DHI groups in single leg stance time. Post hoc correlations of functional reach and single leg stance time. Post hoc correlations of functional reach and single leg stance within the two DHI groups showed a higher correlation in group 1 (DHI < or = 49/100), with r equals 0.65 (P < or = 0.01), than in group 2 (DHI > or = 50/100), with r equals 0.38 (P = 0.20). The study found a highly significant, moderate correlation between functional reach distance and single leg stance times in patients with peripheral vestibular disease. These results support the use of FR as an additional assessment tool with patients who have peripheral vestibular disease.

Adult↗

PubMed1998

Construction of a reach-to-grasp.

Reaching out to grasp an object requires the coordinated action of many different areas of the brain. Each area probably makes a unique contribution to the control of limb movement. We have studied the discharge of interpositus, the output nucleus of intermediate cerebellum, and magnocellular red nucleus, which connects interpositus to the spinal cord. The neurons in these areas discharge at high rates only if a hand movement is included with the reach, and discharge pattern is similar regardless of reach direction. Therefore, interpositus and magnocellular red nucleus are involved primarily in grasp control during the reach-to-grasp; other areas must be controlling the reach. Several other areas of the brain, including the reticular formation, rostral mesencephalon, superior colliculus and motor cortex, are active during reaching. The output from these descending systems converges on interneurons at spinal level C1 and C2 which, in turn, project to level C6, where motor neurons innervating shoulder muscles are located. We hypothesize that reach control is achieved by the convergence of multiple descending pathways onto a complex spinal interneuronal system.

Animals↗

PubMed2006

Preferential reaching across regions of hemispace in adults and children.

The purpose of the current study was to examine hand selection during reaching in children utilizing a developmental version of the preferential reaching paradigm (Bryden, Pryde, & Roy, 2000). A cross-sectional sample of eighty right-handed participants (ranging in age from 3 to 20 years) were asked to reach to objects located in different regions of hemispace. Each participant was asked to carry out two different actions, varying in degree of complexity, on the objects while the experimenter observed, which hand was used to perform each of the tasks. A repeated-measures ANOVA revealed that reaching towards the midline and ipsilateral positions in hemispace resulted in significantly more preferred hand reaches than reaching towards contralateral hemispace, regardless of age and task. With respect to age group effects, it was found that the 6 and 7 year olds and the 9 and 10 year olds relied heavily on their preferred hand to perform the task, indicating that hand selection in these children was driven primarily by motor dominance. In comparison, the youngest children and adults used their nonpreferred hand more frequently in contralateral space, indicating that object proximity cues or a hemispheric bias was driving hand selection. The implications of these findings for understanding hand preference and skill were discussed in terms of motor dominance versus spatial reasoning theory of hand selection in unimanual reaching.

Adolescent↗

PubMed1993

Transformations between visual and kinesthetic coordinate systems in reaches to remembered object locations and orientations.

The abilities of human subjects to perform reach and grasp movements to remembered locations/orientations of a cylindrical object were studied under four conditions: (1) visual presentation of the object-reach with vision allowed; (2) visual presentation-reach while blindfolded; (3) kinesthetic presentation of the object-reach while blindfolded and (4) kinesthetic presentation-reach with vision. The results showed that subjects were very accurate in locating the object in the purely kinesthetic condition and that directional errors were low in all four conditions; but, predictable errors in reach distance occurred in conditions 1,2, and 4. The pattern of these distance errors was similar to that identified in previous research using a pointing task to a small target (i.e., overshoots of close targets, undershoots of far targets). The observation that the pattern of distance errors in condition 4 was similar to that of conditions 1 and 2 suggests that subjects transform kinesthetically defined hand locations into a visual coordinate system when vision is available during upper limb motion to a remembered kinesthetic target. The differences in orientation of the upper limb between target and reach positions in condition 3 were similar in magnitude to the errors associated with kinesthetic perceptions of arm and hand orientations in three-dimensional space reported in previous studies. However, fingertip location was specified with greater accuracy than the orientation of upper limb segments. This was apparently accomplished by compensation of variations in shoulder (arm) angles with oppositely directed variations in elbow joint angles. Subjects were also able to transform visually perceived object orientation into an appropriate hand orientation for grasp, as indicated by the relation between hand roll angle and object orientation (elevation angle). The implications of these results for control of upper limb motion to external targets are discussed.

Adolescent↗

PubMed1988

The effects of unilateral brain damage on visually guided reaching: hemispheric differences in the nature of the deficit.

Groups of patients suffering from unilateral damage to the left or right cerebral hemisphere were compared to a group of age-matched normal controls in a visually guided pointing task. Subjects were required to reach quickly and accurately to small visual targets as soon as they appeared on the screen in front of them. All reaches, which were quite unrestricted, were videotaped by rotary-shutter cameras and analyzed by a computer-assisted system which allowed analysis of the kinematic parameters of the movement in three-dimensional space. The groups were compared on the basis of their latency to initiate a reaching movement, the accuracy with which they achieved the target's position, and various measures derived from the instantaneous velocity of the movement. Both patient groups were found to be less accurate than controls and to require more time after the target was illuminated to complete the reach. But while the right-hemisphere group took longer to initiate a reach, the kinematic parameters of the movements they produced did not differ from those of the control group. In contrast, the left-hemisphere group did not differ from the control group in the time required to initiate a reaching movement but did require a greater period of time to execute the reach once it had been initiated. It is suggested that the right hemisphere group were deficient in the speed with which they could determine the spatial position of the target, while the left hemisphere group were deficient in their ability to select an appropriate motor program to achieve the target position and/or to monitor the movement and update the motor program as it was being executed.

Adult↗

PubMed2003

The role of vision on hand preshaping during reach to grasp.

During reaching to grasp objects with different shapes hand posture is molded gradually to the object's contours. The present study examined the extent to which the temporal evolution of hand posture depends on continuous visual feedback. We asked subjects to reach and grasp objects with different shapes under five vision conditions (VCs). Subjects wore liquid crystal spectacles that occluded vision at four different latencies from onset of the reach. As a control, full-vision trials (VC5) were interspersed among the blocked vision trials. Object shapes and all VCs were presented to the subjects in random order. Hand posture was measured by 15 sensors embedded in a glove. Linear regression analysis, discriminant analysis, and information theory were used to assess the effect of removing vision on the temporal evolution of hand shape. We found that reach duration increased when vision was occluded early in the reach. This was caused primarily by a slower approach of the hand toward the object near the end of the reach. However, vision condition did not have a significant effect on the covariation patterns of joint rotations, indicating that the gradual evolution of hand posture occurs in a similar fashion regardless of vision. Discriminant analysis further supported this interpretation, as the extent to which hand posture resembled object shape and the rate at which hand posture discrimination occurred throughout the movement were similar across vision conditions. These results extend previous observations on memory-guided reaches by showing that continuous visual feedback of the hand and/or object is not necessary to allow the hand to gradually conform to object contours.

Adult↗

PubMed2006

Inhibitory control of reaching movements in humans.

Behavioral flexibility provides a very large repertoire of actions and strategies, however, it carries a cost: a potential interference between different options. The voluntary control of behavior starts exactly with the ability of deciding between alternatives. Certainly inhibition plays a key role in this process. Here we examined the inhibitory control of reaching arm movements with the countermanding paradigm. Right-handed human subjects were asked to perform speeded reaching movements toward a visual target appearing either on the same or opposite side of the reaching arm (no-stop trials), but to withhold the commanded movement whenever an infrequent stop signal was presented (stop trials). As the delay between go and stop signals increased, subjects increasingly failed to inhibit the movement. From this inhibitory function and the reaction times of movements in no-stop trials, we estimated the otherwise unobservable duration of the stopping process, the stop signal reaction time (SSRT). We found that the SSRT for reaching movements was, on average, 206 ms and that it varied with the reaching arm and the target position even though the stop signal was a central stimulus. In fact, subjects were always faster to withhold reaching movements toward visual targets appearing on the same side of the reaching arm. This behavior strictly parallels the course of the reaction times of no-stop trials. These data show that the stop and go processes interacting in this countermanding task are independent, but most likely influenced by a common factor when under the control of the same hemisphere. In addition, we show that the point beyond which the response cannot be inhibited, the so-called point-of-no-return that divides controlled and ballistic phases of movement processing, lies after the inter-hemispheric transfer.

Adult↗

PubMed2006

Visual information throughout a reach determines endpoint precision.

People make rapid, goal-directed movements to interact with their environment. Because these movements have consequences, it is important to be able to control them with a high level of precision and accuracy. Our hypothesis is that vision guides rapid hand movements, thereby enhancing their accuracy and precision. To test this idea, we asked observers to point to a briefly presented target (110 ms). We measured the impact of visual information on endpoint precision by using a shutter to close off view of the hand 50, 110 and 250 ms into the reach. We found that precision was degraded if the view of the hand was restricted at any time during the reach, despite the fact that the target disappeared long before the reach was completed. We therefore conclude that vision keeps the hand on the planned trajectory. We then investigated the effects of a perturbation of target position during the reach. For these experiments, the target remained visible until the reach was completed. The target position was shifted at 110, 180 or 250 ms into the reach. Early shifts in target position were easily compensated for, but late shifts led to a shift in the mean position of the endpoints; observers pointed to the center of the two locations, as a kind of best bet on the position of the target. Visual information is used to guide the hand throughout a reach and has a significant impact on endpoint precision.

Arm↗