Adaptation to display rotation and display gain distortions during drawing

The relationship between movement extent and movement direction coding mechanisms was investigated using a visuomotor adaptation paradigm. To determine if these mechanisms are either modular or interdependent, young healthy college students were tested while they performed a visually guided drawing task that incorporated varying combinations of movement distance and direction distortions. Analysis of participants' standardized movement duration, initial directional error, and movement length over the course of the adaptation process revealed a certain degree of interdependence between direction and extent coding mechanisms. Specifically, changes in final adaptation levels and after-effects depended on the order of introduction of the visual distortions. This interaction can be characterized as unidirectional, where alterations in rotational feedback interfere with subsequent adaptation to gain changes, whereas alterations in "display gain" do not significantly impede the adaptation to "display rotation". Moreover, simultaneous exposure to gain and rotational distortions resulted in better learning. The results argue against an independent coding of movement direction and extent during adaptation by the central nervous system.     

Adaptation in Visuomanual Tracking Depends on Intact Proprioception

The role of arm proprioception in motor learning was investigated in experiments in which, by moving the arm, subjects followed the motion of a target displayed on a monitor screen. Adaptive capabilities were tested in visuomanual tracking tasks following alterations in the relationship between the observer's actual arm movement and visual feedback of the arm movement given by a cursor motion on the screen. Tracking performance and adaptive changes, measured in terms of spatiotemporal error, tracking trajectory curvature, and spatial gain, were compared in 7 control subjects (CSs) and in 1 deafferented subject (DS). CSs adapted appropriately to altered visuomanual relationships; those changes were present in trials immediately after restoration of normal scaling. In contrast, although the DS modified his tracking strategy from trial to trial according to the altered conditions, he did not show plastic changes in internal visuomanual scaling. Like the results of prismatic adaptation experiments, the present results suggest that arm proprioception contributes to the plastic changes that follow alterations in the scaling of visuomanual gain.     

Analyzing the kinematics of hand movements in catching tasks—An online correction analysis of movement toward the target’s trajectory

Free, 3-D interceptive movements are difficult to visualize and quantify. For ball catching, the endpoint of a movement can be anywhere along the target’s trajectory. Furthermore, the hand may already have begun to move before the subject has estimated the target’s trajectory, and the subject may alter the targeted position during the initial part of the movement. We introduce a method to deal with these difficulties and to quantify three movement phases involved in catching: the initial, non-goal-directed phase; the goal-directed phase, which is smoothly directed toward the target’s trajectory; and the final, interception phase. Therefore, the 3-D movement of the hand was decomposed into a component toward the target’s trajectory (the minimal distance of the hand to the target’s parabolic [MDHP] trajectory) and a component along this trajectory. To identify the goal-directed phase of the MDHP trajectory, we employed the empirical finding that goal-directed trajectories are minimally jerky. The second component, along the target’s trajectory, was used to analyze the interaction of the hand with the ball. The method was applied to two conditions of a ball-catching task. In the manipulated condition, the initial part of the ball’s flight was occluded, so the visibility of the ball was postponed. As expected, the onset of the smooth part of the movement shifted to a later time. This method can be used to quantify anticipatory behavior in interceptive tasks, allowing researchers to gain new insights into movement planning toward the target’s trajectory.     

On counteradaptation

Often adaptation to artificially altered stimulation takes place because veridical stimulation that produces the same perceptual property that is produced by the altered stimulation is also received. In these cases, an assimilation of the two perceptual processes produced by the two different stimulations (the altered and the veridical) is supposed to be responsible for the adaptation that is achieved. This hypothesis, which was formulated by Wallach and Karsh (1963), would be confirmed by demonstrating a modification of the perceptual process produced by veridical stimulation rather than the one produced by the altered stimulation. We demonstrated this by having S observe in the dark for 20 min a luminous figure that objectively expanded as it moved toward S and contracted as it moved away. But instead of testing for changes in size perception as such, we tested for a change in the relation between accommodation and convergence on the one hand and registered distance on the other. In one experiment, such a change was measured by obtaining estimates of perceived size and depth before and after the adaptation period. Highly significant changes of size and significantly greater changes of stereoscopic depth were obtained. Inasmuch as stereoscopic vision was totally absent from the adaptation conditions, the change in stereoscopic depth that was larger than the size change can only be ascribed to a change in registered distance. In another experiment, we tested for a change in distance by having S point from the side to a vertical line, before and again after the adaptation period, under conditions where only accommodation and convergence could serve as distance cues. Significant changes in the pointing distance were measured, indicating more directly a change in the relation between these oculomotor adjustments and perceived distance. We propose the term counteradaptation for such modification of a perceptual process away from veridicality.     

Control of velocity and position in single joint movements

Previous research on single joint movements has lead to the development of models of control that propose that movement speed and distance are controlled through an initial pulsatile signal that can be modified in both amplitude and duration. However, the manner in which the amplitude and duration are modulated during the control of movement remains controversial. We now report two studies that were designed to differentiate the mechanisms used to control movement speed from those employed to control final position accuracy. In our first study, participants move at a series of speeds to a single spatial target. In this task, acceleration duration (pulse-width) varied substantially across speeds, and was negatively correlated with peak acceleration (pulse-height). In a second experiment, we removed the spatial target, but required movements at the three speeds similar to those used in the first study. In this task, acceleration amplitude varied extensively across the speed targets, while acceleration duration remained constant. Taken together, our current findings demonstrate that pulse-width measures can be modulated independently from pulse-height measures, and that a positive correlation between such measures is not obligatory, even when sampled across a range of movement speeds. In addition, our findings suggest that pulse-height modulation plays a primary role in controlling movement speed and specifying target distance, whereas pulse-width mechanisms are employed to correct errors in pulse-height control, as required to achieve spatial precision in final limb position.     

Adaptation to a direction-dependent visuomotor gain in the young and elderly

Consistent with the widely accepted notion of separate specification of movement amplitude and direction, it has been argued that there is also a categorical difference between adaptation to novel visuomotor rotations and to novel visuomotor gains. In line with this view, ageing seems to affect rotation and gain adaptation differently in that age-related impairments are consistently found for the former, but not for the latter. In this study we ask whether the contrasting findings could also be ascribed to differences in the level of difficulty of gain and rotation adaptation tasks, respectively. In order to increase the difficulty of gain adaptation, younger and older participants had to adapt to a direction-dependent gain transformation. Results revealed direction-dependent adaptation in both groups. More importantly, we replicated the typical findings of age-related impairments of adaptation, but not of aftereffects, that were previously only reported for rotation adaptation. Younger participants also showed superior explicit knowledge regarding the novel visuomotor mapping as compared to the older participants. We show that this knowledge was used by younger participants to selectively augment adaptive shifts. Finally, our findings suggest that the difficulty of the novel visuomotor transformation and, related to this, the involvement of explicit knowledge in adaptation is critical for age-related changes to show up, but not the type of adaptation task, rotation and gain adaptation, respectively.     

Reafference learning in the presence of exafference

Reafference learning has been demonstrated most clearly in the case of position-constancy adaptation in which the only stimulus change is caused by the subject’s own movoment. The present study used the more ecologically representative training situation in which only part of the stimulus change is caused by the subject (reafference), while part of it is caused by an independent source (exafference). The exafference varied the space relation between subject movement and optical movement or the time relation between those two. In both cases, reafference learning was not affected by the exafference, and the subject’s varied training experience resulted in a fixed expected optical movement and a fixed expected time lag.     

Interlimb differences in visuomotor and dynamic adaptation during targeted reaching in children

While a number of studies have focused on movement (a)symmetries between the arms in adults, less is known about movement asymmetries in typically developing children. The goal of this study was to examine interlimb differences in children when adapting to novel visuomotor and dynamic conditions while performing a center-out reaching task. We tested 13 right-handed children aged 9–11 years old. Prior to movement, one of eight targets arranged radially around the start position was randomly displayed. Movements were made either with the right (dominant) arm or the left (nondominant) arm. The children participated in two experiments separated by at least one week. In one experiment, subjects were exposed to a rotated visual display (30° about the start circle); and in the other, a 1 kg mass (attached eccentrically to the forearm axis). Each experiment consisted of three blocks: pre-exposure, exposure and post-exposure. Three measures of task performance were calculated from hand trajectory data: hand-path deviation from the straight target line, direction error at peak velocity and final position error. Results showed that during visuomotor adaptation, no interlimb differences were observed for any of the three measures. During dynamic adaptation, however, a significant difference between the arms was observed at the first cycle during dynamic adaptation. With regard to the aftereffects observed during the post-exposure block, direction error data indicate considerably large aftereffects for both arms during visuomotor adaptation; and there was a significant difference between the arms, resulting in substantially larger aftereffects for the right arm. Similarly, dynamic adaptation results also showed a significant difference between the arms; and post hoc analyses indicated that aftereffects were present only for the right arm. Collectively, these findings indicate that the dominant arm advantage for developing an internal model associated with a novel visuomotor or dynamic transform, as previously shown in young adults, may already be apparent at 9 to 11-year old children.     

Accuracy constraints upon rapid elbow movements

Kinematic and myoelectric variables associated with rapid elbow-flexion movements of various distances to targets of various widths were studied. The movement time in these experiments conformed to Fitts' law: movement time increased with target distance and decreased with target width. Peak movement velocity, electromyograph (EMG) duration, and EMG quantity were poorly described by Fitts' law, for increases in target width were accompanied by increases in these variables. We show with regression equations, using separate weighting coefficients, that kinematic and myoelectric variables can be related to distance and target width. The use of distance and target width as independent variables allows us to suggest that the literature does not agree on the relation between EMG and distance moved partly because of the influences of the target on this relationship. We propose that human voluntary movement involves a subject "strategy," or set of internal constraints, that affect movement outcome. Significant elements of this strategy, such as how accurately to perform the task, may not be recognized or controlled in many movement paradigms, in spite of uniform instruction to subjects and similar apparatus.     

The micro-structure of tapping movements in children

In order to investigate the development of movement speed in relation to movement organization, children of 5, 6, 7, 8 and 9 years of age and adults carried out a reciprocal tapping task, in which time pressure and distance were manipulated. The duration, velocity, acceleration and accuracy of the movements were compared between age groups. Age differences appeared mainly in the homing time, not in the duration of the distance covering movement phase. Accuracy and velocity of the distance covering movement phase differed with age. Time pressure affected the homing time, but not the duration of the distance covering phase. Distance manipulation affected mainly the velocity and duration of the distance covering movement phase and the homing time. In the discussion it is contended that age differences in homing time may be related to both the accuracy of the distance covering movement phase and the rate of information processing of the subject.     

The Micro-Structure of Tapping Movements in Children

In order to investigate the development of movement speed in relation to movement organization, children of 5, 6, 7, 8 and 9 years of age and adults carried out a reciprocal tapping task, in which time pressure and distance were manipulated. The duration, velocity, acceleration and accuracy of the movements were compared between age groups. Age differences appeared mainly in the homing time, not in the duration of the distance covering movement phase. Accuracy and velocity of the distance covering movement phase differed with age. Time pressure affected the homing time, but not the duration of the distance covering phase. Distance manipulation affected mainly the velocity and duration of the distance covering movement phase and the homing time. In the discussion it is contended that age differences in homing time may be related to both the accuracy of the distance covering movement phase and the rate of information processing of the subject.     

Emergence of spontaneous anticipatory hand movements in a probabilistic environment

In this article, we present a novel experimental approach to the study of anticipation in probabilistic cuing. We implemented a modified spatial cuing task in which participants made an anticipatory hand movement toward one of two probabilistic targets while the (x, y)-computer mouse coordinates of their hand movements were sampled. This approach allowed us to tap into anticipatory processes as they occurred, rather than just measuring their behavioral outcome through reaction time to the target. In different conditions, we varied the participants’ degree of certainty of the upcoming target position with probabilistic pre-cues. We found that participants initiated spontaneous anticipatory hand movements in all conditions, even when they had no information on the position of the upcoming target. However, participants’ hand position immediately before the target was affected by the degree of certainty concerning the target’s position. This modulation of anticipatory hand movements emerged rapidly in most participants as they encountered a constant probabilistic relation between a cue and an upcoming target position over the course of the experiment. Finally, we found individual differences in the way anticipatory behavior was modulated with an uncertain/neutral cue. Implications of these findings for probabilistic spatial cuing are discussed.     

Auditory motion aftereffects

Observers were adapted to simulated auditory movement produced by dynamically varying the interaural time and intensity differences of tones (500 or 2,000 Hz) presented through headphones. At lO-sec intervals during adaptation, various probe tones were presented for 1 sec (the frequency of the probe was always the same as that of the adaptation stimulus). Observers judged the direction of apparent movement (“left” or “right”) of each probe tone. At 500 Hz, with a 200-deg/sec adaptation velocity, “stationary” probe tones were consistently judged to move in the direction opposite to that of the adaptation stimulus. We call this result an auditory motion aftereffect. In slower velocity adaptation conditions, progressively less aftereffect was demonstrated. In the higher frequency condition (2,000 Hz, 200-deg/sec adaptation velocity), we found no evidence of motion aftereffect. The data are discussed in relation to the well-known visual analog-the “waterfall effect.” Although the auditory aftereffect is weaker than the visual analog, the data suggest that auditory motion perception might be mediated, as is generally believed for the visual system, by direction-specific movement analyzers.     

Coordination Between Breathing and Finger Tracking in Man

Arm and leg movements are known to produce temporal pattern changes of breathing. This can be interpreted as coordination, as defined by von Holst (1939). The aim of the present study was to find whether breathing exerts an influence in a reverse direction on a nonrespiratory movement as well. A pursuit tracking test was used, and test individuals (N = 19) were instructed to track a visually presented step function by flexion or extension of their right index finger. Velocity and precision of the step responses proved to be dependent on their relation to the breathing time course; the differences between inspiratory and expiratory responses were smaller than those within each half-cycle. The movements were performed more rapidly and more precisely in about the middle of each half-cycle than immediately after the respiratory phase transition or during the second half of each inspiration or expiration. Discontinuous short-lasting motor actions exerted a coordinative influence on respiration comparablewith that of periodical events: Breaths coinciding with step responses were shortened, preferably when the preset step was given early in the inspiration. It was hypothesized that the reciprocal effect between both motor actions changes periodically. In the first part of each respiratory half-cycle, the respiratory rhythm exerts only a weak influence on additional movements, but it can be altered easily by simultaneous motor processes. Toward the respiratory phase-switching, the respiratory rhythm behaves more stably against coordinative influences and becomes capable of impairing an additional movement.     

Effects of movement distance,duration, velocity,and type on action prediction in 12-month-olds

The goal of the present study was to test the influence of the spatial and temporal dynamics of observed manual actions on infants’ action prediction. Twelve-month-old infants were presented with reach-and-transport actions performed by a human agent. Movement distance, duration, and – resulting from the two – movement velocity were systematically varied. Action prediction was measured via the latency of gaze arrival at target in relation to agent’s hand. The results showed a general effect of all parameters on the infants’ perception of goal-directed actions: Infants were more likely to predict the action goal the longer the movement distance was, the longer the movement duration was, and the slower the movement velocity was. In addition, they were more likely to predict the goal of a reaching than a transport action. The present findings extent previous findings by showing that infants are not only sensitive to differences in distances, durations, and velocities at early age but that these factors have a strong impact on the prediction of the goal of observed actions.     

社会合作信息对距离知觉的影响

为探讨社会合作信息对距离知觉的影响,本研究通过两个实验,采用动态追逐场景,对两个追逐者之间的交互模式(或合作或单独追逐同一目标)与追逐目标的存在与否进行了操作。结果发现,相比随机运动和单独追逐,存在合作关系的两个追逐者间的距离被知觉得更远,即存在距离的扩张效应(实验1),且该效应不能由底层的物理特征所解释(实验2)。该结果揭示,社会合作信息使得知觉距离被扩张,其可帮助理解视觉的适应性机制。     

The timing of natural prehension movements

Prehension movements were studied by film in 7 adult subjects. Transportation of the hand to the target-object location had features very similar to any aiming arm movement, that is, it involved a fast-velocity initial phase and a low-velocity final phase. The peak velocity of the movement was highly correlated with its amplitude, although total movement duration tended to remain invariant when target distance was changed. The low-velocity phase consistently began after about 75% of movement time had elapsed. This ration was maintained for different movement amplitudes. Formation of the finger grip occurred during hand transportation. Fingers were first stretched and then began to close in anticipation to contact with the object. The onset of the closure phase was highly correlated to the beginning of the low velocity phase of transportation. This pattern for both transportation and finger grip formation was maintained in conditions whether visual feedback from the moving limb was present or not. Implications of these findings for the central programming of multisegmental movements are discussed.     

Effects of Visual Error Timing on Smooth Pursuit Gain Adaptation in Humans

Smooth pursuit (SP) is one of the precise oculomotor behaviors when tracking a moving object. Adaptation of SP is based on a visual-error driven motor learning process associated with predictable changes in the visual environment. Proper timing of a sensory signal is an important factor for adaptation of fine motor control. In this study, we investigated whether visual error timing affects SP gain adaptation. An adaptive change in SP gain is produced experimentally by repeated trials of a step-ramp tracking with 2 different velocities (double-velocity paradigm). The authors used the double-velocity paradigm where target speed changes 400 or 800 ms after the target onset. The results show that SP gain changed in a certain time window following adaptation. The authors suggest that SP adaptation shown in this study is associated with timing control mechanisms.     

Motion prediction and the velocity effect in children

In coincidence‐timing studies, children have been shown to respond too early to slower stimuli and too late to faster stimuli. To examine this velocity effect, children aged 6, 7.5, 9, 10.5, and adults were tested with two different velocities in a prediction‐motion task which consisted of judging, after the occlusion of the final part of its path, the moment of arrival of a moving stimulus towards a specified position. A similar velocity effect, resulting in later responses for the faster velocities than for the slower, was found primarily in the three younger groups of children (for the longer occlusion conditions: 600–1,320 milliseconds). However, this effect was not seen in all children in these groups. Individual analyses showed that this velocity effect, when present, is linked to the use of distance rather than time information, or to the confusion between these in extrapolating the occluded trajectories. The tendency to use one type of information or the other is a good predictor of accuracy and variability in this task and a good indicator of the development stage of the participants. Across development, children tend to initially use distance information with poor accuracy but relative consistency in responses. In a second stage, they use time and distance information alternatively across trials trying to find a better source of information with still poor accuracy and now great variability. In a final stage, they use time information to reach consistency and accuracy in their responses. This chronology follows the stages proposed by Savelesbergh and Van der Kamp (2000) explaining development with an initial stage of ‘freezing’ non‐optimal relationships between information and movement, then a ‘freeing’ stage during which new solutions are searched for, and finally an ‘exploiting’ stage with an optimal relationship between information and movement.     

Kinematic analysis of multiple constraints on a pointing task

The current experiment suggests that the speed/accuracy tradeoff is composed of two classes of constraints, effector and task. We examined the effects of movement distance, target size, orientation of the movement in the workspace, and C-D gain on the kinematics of discrete pointing movements made with computer mouse. It was found that target size influenced the shape of velocity profiles by elongating the duration of the corrective sub-movement phase, while movement distance scaled the entire velocity curve without affecting its shape. C-D gain and orientation of the movement exhibited two kinds of effects: an overall scaling of the velocity curve and a change in its shape. We conclude that target size is a task constraint and movement distance is an effector constraint, while movement orientation exhibited characteristics of both. C-D gain by itself was not a constraint, but interacted with both task and effector constrains. These results highlight the roles of biomechanical and information processing factors in the speed/accuracy tradeoff.