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PubMed2004

Movement velocity effects on kinaesthetic localisation of spatial positions.

In the present study, we examined how subjects locate spatial positions and code them in short-term memory. In the first experiment, blindfolded subjects were asked to perform movements in the near or far peripersonal space (criterion movement, CM). Then, subjects had to reach the end-point of CM (reproduction movement, RM). Movements could be performed either slowly or rapidly. Also, CM and RM could be performed with the same (congruent conditions) or different velocity (incongruent conditions). The results showed that performance was accurate in the two congruent conditions. Conversely, in the incongruent conditions, subjects made undershoot errors when the CM was fast and overshoot errors when it was slow. In the second experiment, blindfolded subjects also performed CM and RM in congruent or incongruent conditions. However, the CM and RM could start from the same or different position. We found again undershoot errors when the CM was fast and RM was slow and overshoot errors in the reverse condition. The results of both experiments suggest that the information about movement velocity contributes to the kinaesthetic coding in memory of a spatial location to be reached with arm movement.

Adult↗

PubMed2004

Maintaining spatial body alignment on a rotating platform by means of active counter-circling: role of vestibular and podokinesthetic afferents.

We investigated the behaviour of vision-deprived human subjects who try to maintain their horizontal alignment in space on a rotating platform by stepping about their own axis in counter-direction ('podomotor counter-rotation'), and we ask which of two alternative hypotheses best explains this behaviour. (1) The feedback hypothesis assumes that the podomotor counter-rotation is controlled by negative feedback of vestibular signals from the horizontal canals. (2) The reconstruction hypothesis holds that the vestibular cue first is combined with leg proprioceptive afferents signalling the individual's rotation on the platform ('podokinesthetic cue') in a way that reconstructs the platform's motion in space for internal representation; a negative (direction-inverted) copy of this representation then would drive the counter-rotation. Subjects were exposed to three different velocity profiles of platform rotation: VC, constant velocity rotation with sudden onset and offset; VS, sinusoidal rotation; VN, pseudorandom noise sequences. The subjects' response (i.show $132#e., their active self-rotation on the platform) to the onset and offset of VC rotations was reminiscent of a first-order lead system. Specifically, after rotation onset subjects immediately began to step on the platform in opposite direction; initially, the velocity of this response matched that of platform rotation, leading to a fairly good stabilisation of subjects' alignment in space. However, this response declined exponentially; consequently, subjects began to increasingly rotate in space along with the platform, ultimately stepping in place on the platform. After rotation offset, subjects immediately began to step around on the now stationary platform so as to continue their previous rotation in space; this response again declined exponentially until subjects became gradually stable again with respect to space. Within subjects, the time constant (tau) of these responses was similar for onset and offset. Across subjects it exhibited a conspicuous variability, ranging from 7 s to virtually infinity. The responses to VS and VN rotations were closely correlated to what could be predicted for each individual from his tau during VC on the assumption of a first-order lead system. We conclude that the mechanism stabilising body orientation basically is linear (no prediction with sinusoidal rotation, no extrapolation of constant velocity rotation). A comparison of the experimental results with simulations of the feedback hypothesis and of the reconstruction hypothesis suggests that the reconstruction hypothesis is a more likely description of the underlying processing of the vestibular and podokinesthetic cues.

Adult↗

PubMed2004

What the hand can't tell the eye: illusion of space constancy during accurate pointing.

When we press an elevator button or pick up a coffee cup, different visual information is used to guide our reach and to form our conscious experience of these objects. But can the information guiding our hand be brought into awareness? The fact that we can see and feel our own hand in action suggests that it might be possible. However, the dual visual systems theory claims that on-line control of movement is governed by the dorsal stream of visual processing, which is largely unconscious. Two experiments are presented as strong tests of the hypothesis that the visual information guiding on-line pointing in healthy human adults is inaccessible for conscious report. Results show that participants are incapable of consciously accessing the information used in pointing, even though they can see and feel their hands in action and accurate performance depends on it.

Biomechanical Phenomena↗

PubMed2005

Factors affecting the size of the detour effect in the kinaesthetic perception of Euclidean distance.

Three experiments investigated the mechanisms by which we estimate Euclidean distances on the basis of kinaesthetic cues. In all experiments, blindfolded participants followed straight and curvilinear paths with a stylus. Then, with a straight response movement, they estimated the distance between the end-points of the previously explored path. Experiment 1 was designed to validate the hypothesis-made on the basis of results from a previous study-that errors in the kinaesthetic estimations of distances (detour effect) originate from the difficulty to decompose the displacement vector into relevant and irrelevant components, which would become more severe at points of inflection. Using elliptic paths (no inflections), we demonstrated that errors are indeed reduced considerably. The role of the orientation of the work plane was investigated in Experiment 2 in which the same paths used in our previous study were oriented in the frontal rather than the horizontal plane. The results indicate that the detour effect is independent of the orientation. Moreover, despite the asymmetry that gravity introduces between upward and downward movements, errors in the two directions are almost identical. Experiment 3 addressed two issues. First, we demonstrated that introducing a delay between the exploration of the path and the response did not alter significantly the pattern of errors. By contrast, we demonstrated that errors are severely reduced when the number of paths to be explored is reduced by half. The results of the three experiments are discussed within the context of current theories of sensori-motor coding.

Adolescent↗

PubMed2005

Kinesthetic memory in distance reproduction task: importance of initial hand position information.

The role of the initial hand position in planning and implementation of a goal-directed movement is a matter of debate. We designed a non-visually guided repetitive reaching movement task to investigate the role of proprioceptive information of the initial or end hand position in implementation of kinesthetic memory. The experimental design consisted four experiments. Each experiment consisted two phases: the training phase and the test phase. In the training phase the subjects were asked to learn and memorize the distance between start and end points by moving their hands ten times between them. In the test phase, the end point was removed, and starting from the same initial position, the subjects were asked to reproduce the memorized distance. In all experiments, varied conditions called "mask phase" preceded the test phase: a 5-s delay in experiment 1, shifting both initial and end points while keeping the distance constant in experiment 2, shifting only the end point, while keeping the initial point constant in experiment 3 and shifting only the initial point and keeping the end point constant in experiment 4. In comparison to experiment 1 (which was considered as the control group), no significant error in distance reproduction occurred in experiment 3, while experiments 2 and 4 showed significant error. These findings mean that although the distance information was available during the mask phase of experiment 2, subjects could not efficiently use this information to reproduce the distance. The other two experiments suggest that this error was caused by changing the initial hand position and not the end point. We conclude that in a kinesthetic-guided distance reproduction task, the initial hand position is more important for implementation of distance memory rather than the end point.

Adult↗

PubMed2005

Changes in perception of active but not passive turning following stepping on the rotating treadmill.

The purpose of this work was to determine whether walking on a rotating disc would cause changes in perception of active and passive turning. Ten healthy control subjects wore a blindfold and earplugs while completing trials of active and passive turning. For active conditions, subjects were told the direction and amplitude of the desired turn and then attempted to turn in place the specified amount via actively stepping. For passive conditions, subjects were told that the disc they stood on would turn and they were to press a button when they had traveled the specified amplitude. Subjects completed active and passive trials to the left and right with amplitudes of 90, 180, 270, and 360 degrees. Subjects then stepped in place for 15 min on a disc rotating clockwise at 90 degrees /s, after which they repeated the trials of active and passive turning. Following rotating treadmill stimulation, subjects asked to turn in the direction opposite disc rotation (i.e., to the left) consistently and significantly overshot their targets in active trials. There were no changes in accuracy of active turning to the right or passive turning in either direction. This indicates that adaptation to the rotating treadmill is expressed even when subjects have a conscious intent to turn. The positive after-effects of the rotating treadmill add to the intended active turning in the direction of the after-effect but there is no decrement in active turning in the direction opposite the after-effect.

Adult↗

PubMed2006

The effect of enslaving on perception of finger forces.

The primary purpose was to examine the effect of enslaving on finger force perception during isometric finger force production using an ipsilateral force-matching paradigm. Fourteen subjects were instructed to produce varying levels of reference forces [10, 20, 30, and 40% maximal voluntary contraction (MVC)] force using one finger (index, I or little, L) and to reproduce these forces using the same finger (homo-finger tasks, I/I and L/L) or a different finger (hetero-finger tasks, I/L and L/I). Forces of all fingers were recorded. During homo-finger tasks, no differences were found in force magnitude or relative level of force (expressed as a proportion of MVC). The index finger matching force magnitudes were greater than the little finger reference force magnitudes, with significantly lower levels of relative force during L/I tasks; while the little finger matching forces underestimated the index finger reference forces with significantly higher levels of relative force during I/L tasks. The difference in the matching and reference forces by the instructed finger(s), i.e., matching error, was larger in hetero-finger tasks than in homo-finger tasks, particularly at high reference force levels (30, 40% MVC). When forces of all fingers were considered, enslaving (uninstructed finger forces) significantly minimized matching errors of the total force during both I/L and L/I hetero-finger tasks, especially at high reference force levels. Our results show that there is a tendency to match the absolute magnitude of the total force during ipsilateral finger force-matching tasks. This tendency is likely related to enslaving effects. Our results provide evidence that all (instructed and uninstructed) finger forces are sensed, thus resulting in perception of the absolute magnitude of total finger force.

Adult↗

PubMed2006

The haptic reproduction of orientations in three-dimensional space.

This research studied the haptic perception of orientations in space rather than in a plane. It aimed at identifying the nature of the system of coordinate used to represent an orientation in space, when two parameters are necessary to code an orientation. Blindfolded participants inserted the tip of the index finger in a thimble mounted at the extremity of a haptic interface, explored the orientation of a "virtual rod" with to-and-fro movements and, after a short delay, reproduced the same orientation with the same fingertip in the absence of the virtual rod. Globally, the haptic reproduction of orientations was anisotropic. When the reproduction of orientations was carried out in the frontal plane, a classical oblique effect (lower performance for the diagonal orientations than for the vertical and horizontal orientations) occurred. When the reproduction of orientations was carried out in space, orientations seemed to be coded in a coordinate system based on the sagittal plane.

Adult↗

PubMed2005

Postural stabilization from fingertip contact II. Relationships between age, tactile sensibility and magnitude of contact forces.

In the present report, we extend our previous observations on the effect of age on postural stabilization from fingertip contact (Exp Brain Res 157 (2004) 275) to examine the possible influence of sensory thresholds measured at the fingertip on the magnitude of contact forces. Participants (young, n=25, 19-32 years; old, n=35, 60-86 years) underwent psychophysical testing of the right index finger to determine thresholds for spatial acuity, pressure sensitivity and kinesthetic acuity. Spatial acuity was determined from the ability to detect gaps of different widths, while Semmes-Weinstein monofilaments were used for pressure sensitivity. Kinesthetic acuity was determined by asking participants to discriminate plates of different thicknesses using a thumb-index precision grip. These tests were selected on the basis that each reflected different sensory coding mechanisms (resolution of spatial stimuli, detection of mechanical forces and integration of multi-sensory inputs for hand conformation) and thus provided specific information about the integrity and function of mechanoreceptive afferents innervating the hand. After log transformation, thresholds were first examined to determine the influence of age (young and old) and gender (male, female) on tactile acuity. Sensory thresholds were then entered into multiple linear regression models to examine their ability to predict fingertip contact forces (normal and tangential) applied to a smooth surface when subjects stood with eyes closed on either a firm or a compliant support surface. As expected, age exerted a significant effect (p<0.01) on all three thresholds, but its impact was greater on spatial acuity than on pressure sensitivity or kinesthetic acuity. Gender had a marginal impact on pressure sensitivity thresholds only. The regression analyses revealed that tactile thresholds determined at the index fingertip accounted for a substantial proportion of the variance (up to 30%) seen in the contact forces deployed on the touch-plate, especially those exerted in the normal direction. The same analyses further revealed that much of the variance explained by the models arose from inter-individual differences in tactile spatial acuity and not from differences in pressure sensitivity or in kinesthetic acuity. Thus, of all three tests, the spatial acuity task was the most sensitive at detecting differences in hand sensibility both within and between age groups and, accordingly, was also better at predicting the magnitude of fingertip forces deployed for postural stabilization. Since spatial acuity is critically dependent upon innervation density, we conclude that the degree of functional innervation at the fingertip was likely an important factor in determining the capacity of older participants to use contact cues for stability purposes, forcing the most affected individuals to exert unusually high pressures in order to achieve stabilization in the presence of reduced tactile inputs arising from contact with the touched surface.

Adult↗

PubMed2005

Temporal constraints on interactions across kinaesthetic channels.

We investigated the effect of correlation in background noise on the ability of participants to detect a kinaesthetic target on the index fingers of their hands. Participants had to judge whether the target (a smoothed ramp with quarter-sine onset and offset), was on the left or right finger (experiments 1 and 2). These targets were embedded in noise generated by pseudo-random up-down movements of both the left and right fingers. Positive correlation between the noise on the left and right fingers aided discrimination of the target signal relative to when the noise was uncorrelated. However, this benefit of positive correlation was subject to temporal limitations and diminished with increasing lag between the noise on the fingers (experiment 2). Tests of explicit detection of correlation in kinaesthetic noise (experiment 3) showed a similar pattern, with detection of correlation decreasing with the temporal lag between the noise on the fingers. The results suggest that kinaesthetic signal detection involves sensory integration across the fingers within a limited temporal window.

Adult↗

PubMed2005

Reproduction of ON-center and OFF-center self-rotations.

In self-rotation reproduction tasks, subjects appear to estimate the displacement angle and then reproduce this angle without necessarily replicating the entire temporal velocity profile. In contrast, subjects appear to reproduce the entire temporal velocity profile during linear motion stimulating the otoliths. To investigate what happens during combined rotation and translation, we investigated in darkness the central processing of vestibular cues during eccentric rotation. Controlling a centrifuge with a joystick, nine healthy subjects were asked to reproduce the angle of the previously imposed rotation. Rotations were either ON-center, or 50 cm OFF-center with inter-aural centripetal acceleration. Rotation duration was either variable (proportional to the traveled angle), or constant. We examined whether the stimulation of the otoliths during OFF-center rotation changes self-rotation reproduction, and whether rotation duration is processed differently by the nervous system with and without otolith stimulation. As postulated, the subjects indeed reproduced more closely the stimulus velocity profile when OFF-center. But the primary result is that the additional supra-threshold linear acceleration cues, measured by the otoliths, did not improve performance. More specifically, to our surprise, the ability to reproduce rotation angle degraded slightly in the presence of additional information from the otolith organs, with the linear acceleration cues appearing to interfere with the reproduction of movement duration.

Acceleration↗

PubMed2005

Changes in the centrifugal gating effect on somatosensory evoked potentials depending on the level of contractile force.

In this study, we investigated the somatosensory evoked potentials (SEPs) during the preparatory period of self-initiated plantar flexion at different force levels of muscle contraction and elucidated the mechanism behind the centrifugal gating effect on somatosensory information processing. We recorded SEPs following stimulation of the tibial nerve at the popliteal fossa during the preparatory period of a 20% maximal voluntary contraction (MVC) and 50% MVC. The preparatory period was divided into two sub-periods based on the components of movement-related cortical potentials, the negative slope (NS sub-period) and the Bereitschaftspotential (BP sub-period). The subjects were instructed to concentrate on the movement and not to pay attention to the continuous electrical stimulation. Pre-movement SEPs were averaged separately during the two sub-periods under each MVC condition. The mean amplitudes of BP and NS were larger during the 50% MVC than the 20% MVC. As for the components of SEPs, during the NS sub-period the amplitude of P30 under the 50% MVC and N40 under both conditions were significantly smaller than that in the stationary sequence, and N40 amplitude was significantly smaller during the 50% MVC than the 20% MVC. During the BP sub-period, the amplitude of P30 and N40 during the 50% MVC was significantly smaller than during the stationary sequence, while it was not significantly different between the 20% and 50% MVCs. In conclusion, the extent of the centrifugal gating effect on SEPs was dependent on the activities of motor-related areas, which generated the NS and BP.

Adult↗

PubMed2005

Identifying brain regions for integrative sensorimotor processing with ankle movements.

The objective of this study was to define cortical and subcortical structures activated during both active and passive movements of the ankle, which have a fundamental role in the physiology of locomotion, to improve our understanding of brain sensorimotor integration. Sixteen healthy subjects, all right-foot dominant, performed a dorsi-plantar flexion task of the foot using a custom-made wooden manipulandum, which enabled measurements of the movement amplitude. All subjects underwent a training session, which included surface electromyography, and were able to relax completely during passive movements. Patterns of activation during active and passive movements and differences between functional MRI (fMRI) responses for the two types of movement were assessed. Regions of common activation during the active and passive movements were identified by conjunction analysis. We found that passive movements activated cortical regions that were usually similar in location to those activated by active movements, although the extent of the activations was more limited with passive movements. Active movements of both feet generated greater activation than passive movements in some regions (such as the ipsilateral primary motor cortex) identified in previous studies as being important for motor planning. Common activations during active and passive movements were found not only in the contralateral primary motor and sensory cortices, but also in the premotor cortical regions (such as the bilateral rolandic operculum and contralateral supplementary motor area), and in the subcortical regions (such as the ipsilateral cerebellum and contralateral putamen), suggesting that these regions participate in sensorimotor integration for ankle movements. In future, similar fMRI studies using passive movements have potential to elucidate abnormalities of sensorimotor integration in central nervous system diseases that affect motor function.

Adult↗

PubMed2005

Temporal discrimination of two passive movements in humans: a new psychophysical approach to assessing kinaesthesia.

Percutaneous electrical stimulation of the motor point of the first dorsal interosseous muscle (FDI) was used to produce a non-painful contraction of the FDI muscle that caused index finger abduction movement but no radiating cutaneous paraesthesias or sharp sensations localized to joints. Pairs of stimuli separated by different time intervals were given and subjects were asked to report whether they perceived a single or a double index finger abduction movement. The threshold value was the shortest interval for which the subjects reported two separate index finger abduction movements. Temporal discrimination movement thresholds (TDMT) were measured for both right and left hand. To assess the possible role of muscle and cutaneous afferents in temporal discrimination, we investigated the effects of high-frequency (20 Hz) electrical stimulation of the right ulnar and radial nerves on TDMT. In humans, muscle afferents from FDI are supplied by the ulnar nerve whereas the cutaneous territory overlying the muscle and joint is supplied by the radial and median nerves. Threshold values were not significantly different for right (75.1 ms) and left (75.6 ms) hands. During ulnar and to a lesser extent during radial nerve stimulation, TDMT values were significantly increased (119.2 and 93.5 ms, respectively) compared with baseline conditions (78.0 ms) whereas no changes were observed during median nerve stimulation (80.5 ms). These results suggest that muscle, and in part cutaneous, afferents contribute to temporal discrimination of a dual movement. The technique may provide a useful way of measuring temporal discrimination of kinaesthetic inputs in humans.

Adult↗

PubMed2006

Limits to human movement planning with delayed and unpredictable onset of needed information.

In motor tasks with explicit rewards and penalties, humans choose movement strategies that nearly maximize expected gain (Trommershäuser et al. in J Opt Soc Am A 20:1419-1433, 2003). Here, we examine whether performance is still close to optimal when information about payoffs is not available prior to movement onset. Subjects rapidly touched a target region while trying to avoid hitting an overlapping penalty region placed randomly to the left or right of the target. Subjects received rewards and incurred penalties for hitting the corresponding regions. Late responses (>700 ms) were heavily penalized. The penalty region was displayed 0, 200 or 400 ms after the reward region and the subject could not know where it would be until then. Reaction times to begin the movement after stimulus appearance were constant across conditions. Median reaction times were approximately 200 ms, i.e., the time the penalty was first displayed in the 200 ms delay condition. Performance was compared to that of an optimal movement planner that chooses mean end points to maximize expected gain despite movement variability. In the 0 and 200 ms delay conditions, subjects selected strategies that did not differ significantly from optimal, indicating that humans are able to plan their movements well despite delayed and unpredictable onset of information. Performance dropped below optimal in the 400 ms delay condition, with mean movement end points closer to the penalty region than predicted by the optimal strategy (in the high-penalty condition). We conclude that relevant information concerning the reward structure is required between 200 and 400 ms prior to the end of the movement, but can still be integrated into the movement plan after movement initiation.

Adult↗

PubMed2007

Movement-dependent positioning errors in human elbow joint movements.

Healthy adult humans performed elbow movements in a horizontal plane under a small external extending torque (2.1-3.3 Nm). Test movements (TMs) consisted of slow ramp-and-hold flexions in the absence of visual feedback, with the target joint angle to be remembered from a preceding conditioning movement (CM). The CM was produced by matching two beams on the monitor screen: (1) command representing the target position (a straight line); and (2) a signal from the sensor of the elbow joint angle. Two kinds of CM were applied, which had the same target position (50 degrees in most experiments) but differed in initial positions: (1) fully extended joint (0 degrees, P1 CMs); (2) flexed joint (100 degrees, P2 CMs). In a group of 25 subjects, the target in TMs was usually overshot, with the position errors depending on the CMs: 2.7 +/- 0.6 degree (mean +/- SEM) for P1 CMs, and 10.9 +/- 0.7 degree (P < 0.001) for P2 CMs. Vibration of the elbow flexors substantially diminished the difference between the position errors, amounting to--0.31 +/- 0.5 degree and 2.33 +/- 0.6 degrees, respectively. It is suggested that the observed position errors resulted from after-effects in the activity of muscle spindles in agonist and antagonist muscles, but influence of differences in dynamic components of the afferent signals during oppositely directed approaches to the target cannot be excluded.

Adult↗

PubMed2006

Sensorimotor adaptation in response to proprioceptive bias.

Studies investigating visuo-motor adaptation typically introduce sensory conflicts by manipulating visual information (prisms, cursor gains). The purpose of the present study was to determine whether similar adaptation would be observed when a conflict is created through distortion of the proprioceptive sense, rather than through visual distortion. We used a coordinated movement task that required participants to release thumb and index finger at a specific elbow angle during passive elbow extension. Participants could not see their arm, but were shown a cursor representing the forearm on a video screen. In the proprioceptive group, a sensory conflict was introduced by vibrating the biceps brachii muscle, introducing a discrepancy of approximately 7.5 degrees between the proprioceptively perceived and visually perceived elbow angle. In the visual group, a conflict of similar magnitude was obtained by introducing a gain of 7.5 degrees to the cursor with respect to forearm position. Adaptation was assessed by the presence of plastic changes in release elbow angles following a period of exposure to the sensory conflict (i.e., aftereffects). Both groups showed high accuracy during exposure despite the sensory conflicts. More importantly, the visual group presented large and persistent aftereffects, while the proprioceptive group presented none. We suggest that the proprioceptive group's lack of adaptation was due to the artificial muscle spindle activity resulting from vibration, which prevented visual and proprioceptive signals to be merged into a common frame of reference.

Adaptation, Physiological↗

PubMed2006

Fatigue-induced adaptive changes of anticipatory postural adjustments.

To examine the fatigue-induced adaptive changes (e.g., timing) of anticipatory postural adjustments (APAs), APAs of 30 research participants were recorded before (baseline) and after (post-test) conditions of either rest (control group, n=15) or fatigue (fatigue group, n=15). Muscle fatigue was generated using a dead-lift exercise performed to exhaustion. Self-initiated postural perturbations were induced using a rapid unilateral arm-raising maneuver (focal movement), and APAs were obtained using electromyography (EMG) recorded bilaterally in the lumbar and thoracic paraspinal muscles as well as the hamstring muscles. Postural stability during the focal movement was assessed using a force plate. Results showed that fatigue had no effect on postural stability during the focal movement, and yet caused earlier APA onsets in three of the six muscles evaluated. In spite of early APA activation, the APA EMG integrals of two of the three postural control muscles which exhibited fatigue-induced early APA onsets (T9 and L4 contralateral paraspinals) did not differ between baseline and post-test measures. The findings suggest that early APA onset may enhance postural stability by permitting a longer duration APA which can counteract fatigue-induced decreases in the force-producing capability of muscles that contribute to postural stability.

Adaptation, Physiological↗