A Preliminary Analysis of the Coordination of Reaching, Grasping, and Walking

The purpose of this investigation was to describe the strategies used by individuals when motor systems controlling locomotion and prehension must be used simultaneously to perform a task. Subjects were required to perform five tasks: walk normally, walk and pick up a small object, walk and pick up a large object, pick up a small object from a stationary standing position, and pick up a large object while standing. The grasping and walking movements were videotaped and the frequencies of various behaviors were observed (type of grasp, location of contact with the object, support leg during contact with the object, timing of gaze toward object). Characteristics of the grasp were influenced by object size, not by whether the subject was walking. Gaze was shifted to the object before initiation of reach and this pattern was not influenced by size of the object or movement of the subject. Finally, subjects preferred using an ipsilateral support leg while generating the reach, which is a deviation from normal gait patterns. Findings indicate that the motor control system may be hierarchically organized in such a way that stability of the lower limbs supersedes the control of the movement patterns of an upper limb.

Hand, Eye, and Head Coordination While Pointing to Perturbed Targets

Normal human subjects were required to manually point to small visual targets that suddenly changed location upon finger movement initiation. They pointed either as fast or as accurately as possible. Movements of the eyes were measured by electrooculography, and the movements of the unrestrained limb and head were monitored by an optoelectric system (WATSMART), which allowed for the analysis of kinematic parameters in three-dimensional space. The temporal and kinematic reorganization of each body part in response to the target perturbations were variable, which indicated independent control for each part of the system. That is, the timing and nature of the reorganization varied for each body part. In addition, the pattern of reorganization depended upon the speed and accuracy demands of the movement task. As well, the movement termination patterns (eyes finished first, the finger reached the target, then the head stopped moving) were extremely consistent, indicating that movement termination may be a controlled variable. Finally, no evidence was found to suggest that visual information was used to amend arm movements early (before peak velocity) in the trajectory.

55. Simulation based training of technical surgical skills: A review of a five-year collaborative research program supported by the RCPSC Medical Education Funds

During the past five years, with support from the RCPSC, a collaborative group of researchers conducted projects investigating issues related to simulation based training of technical surgical skills. The aim of this presentation is to review the body of work generated, its significance, and outline future research plans. In all studies, participants were medical students and residents from 3 medical schools in Ontario. First, we successfully demonstrated that trainees benefit from simulation-based practice by improving their ability to multitask. This ability not only increases technical proficiency, but also results in an enhanced ability to learn other aspects of surgery. Second, we showed that the adaptation of learning theories helps in optimizing training curricula by matching the fidelity of a simulator to the trainees’ level of expertise. Third, we provided validation of both expert and computer based methods for assessment. We showed that computer based assessments are sufficient for the evaluation of trainees learning fundamental skills, while expert based measures are more effective in the evaluation of performance on complex technical skills. Finally we demonstrated that examination-induced stress has a facilitating effect on trainees’ skills performance. This body of research lends support for the inclusion of a simulation based approach to training technical skills. It also highlights the importance of the choice of assessment methods. Collectively this work highlights the need for further research in the optimization of training methods by the incorporation of learning theory into the existing training curricula. Related to this, further research in our laboratory will investigate the effects of practice schedule and expert feedback, as well as the role of self-regulated practice in the acquisition of technical surgical skills. Xeroulis GJ, Park J, Moulton CA, Reznick RK, Leblanc V, Dubrowski A. Teaching suturing and knot-tying skills to medical students: a randomized controlled study comparing computer-based video instruction and (concurrent and summary) expert feedback. Surgery 2007; 141(4):442-9. Brydges R, Sidhu R, Park J, Dubrowski A. Construct validity of computer-assisted assessment: quantification of movement processes during a vascular anastomosis on a live porcine model. Am J Surg. 2007; 193(4):523-9. Brydges R, Carnahan H, Backstein D, Dubrowski A. Application of motor learning principles to complex surgical tasks: searching for the optimal practice schedule. J Mot Behav. 2007; 39(1):40-8.

56. Proficiency at the end of practice predicts retention of a technical clinical skills

A debate is emerging regarding the efficacy of proficiency based versus duration based training of technical skills. It is not clear whether the performance level attained at the end of practice (i.e., proficiency criteria), or the overall amount of practice performed during learning will best predict the retention of a technical clinical skill. The skill learned was the single-handed double square-knot. Forty two trainees learned the skill through video-based instruction and were divided into three groups (14 participants per group) each with a specific criterion time to tie the knot (10, 15, and 20 seconds). Practice continued until participants completed the knot within their criterion time. The total number of trials, and the overall practice time required to obtain each respective criterion were recorded during practice. Participants returned one-week later for a timed retention test consisting of one trial of the knot tying skill with no video instruction. A multiple regression analysis tested whether the amount of practice, the total practice time, or the criterion reached at the end of practice was the best predictor of the time taken to perform the skill during retention. This analysis showed that the number of practice trials was highly correlated with total practice time (r = .82, p = .01), therefore total practice time was withdrawn as a predictor variable from the subsequent analysis. The regression showed that the only significant predictor of retention performance was the criterion reached at the end of practice (p = .03). The number of practice trials was not found to significantly predict the retention performance (p = .87). The results support the notion that proficiency based training results in better retention of a technical clinical skill in comparison to duration based approaches. This provides evidence for the introduction of proficiency based educational approaches in technical skills curricula. Jowett N, LeBlanc V, Xeroulis G, MacRae H, Dubrowski A. Surgical skill acquisition with self-directed practice using computer-based video training. Am J Surg. 2007; 193(2):237-42. Gallagher AG, Ritter EM, Champion H, Higgins G, Fried MP, Moses G, Smith CD, Satava RM. Virtual reality simulation for the operating room: proficiency-based training as a paradigm shift in surgical skills training. Ann Surg. 2005; 241(2):364-72. Van Sickle KR, Ritter EM, McClusky DA, Lederman A, Baghai M, Gallagher AG, Smith CD. Attempted establishment of proficiency levels for laparoscopic performance on a national scale using simulation: the results from the 2004 SAGES Minimally Invasive Surgical Trainer-Virtual Reality (MIST-VR) learning center study. Surg Endosc. 2007; 21(1):5-10.

Application of Motor Learning Principles to Complex Surgical Tasks: Searching for the Optimal Practice Schedule

Practice of complex tasks can be scheduled in several ways: as whole-task practice or as practice of the individual skills composing the task in either a blocked or a random order. The authors used those 3 schedules to study 18 participants' learning of an orthopedic surgical task. They assessed learning by obtaining expert evaluation of performance and objective kinematic measures before, immediately after, and 1 week after practice (transfer test). During acquisition, the blocked group showed superior performance for simple skills but not for more complex skills. For the expert-based measures of performance, all groups improved from pretest to posttest and remained constant from posttest to transfer. Measures of the final product showed that the whole-practice group's outcomes were significantly better than those of the random group on transfer. All groups showed better efficiency of motions in the posttest than in the pretest. Those measures were also poorer on the transfer test than on the posttest. The present evidence does not support the contextual interference effect--hypothetically, because of the inherent cognitive effort effect associated with some of the component skills. The authors recommend that surgical tasks composed of several discrete skills be practiced as a whole. The results of this study demonstrate the importance of critically appraising basic theories in applied environments.

Quantification of process measures in laparoscopic suturing

BACKGROUND

Process measures describing the generation of movement are useful for evaluation and performance feedback purposes. This study aimed to identify process measures that differ between novice and advanced laparoscopists while completing a suturing skill.

METHODS

A group of junior and a group of senior residents and fellows in surgery (n = 6) placed 10 laparoscopic sutures in a synthetic model. Process measures were quantified using an opto-electric motion/force sensor assembly that recorded: instrument rotation, applied forces, time, and time delays between force application and instrument rotation.

RESULTS

Advanced trainees showed increased instrument rotation, higher peak applied force, and faster performance compared to novices (alll p < .01). However, over trials, only novices showed adaptations for instrument rotation and total time (interactions at p < .01) with no adaptation for the force application. The difference between the moments of force application and instrument rotation was not sensitive to participant training.

CONCLUSIONS

Movement process measures can enhance our understanding of early adaptation processes and how such factors might be used as feedback to facilitate skill acquisition.

Structural flexibility of laparoscopic instruments: implication for the design of virtual reality simulators

Laparoscopic training, under simulated settings, benefits from high fidelity models of the actual environment. This study was aimed at reducing uncertainty in the displacement and loads experienced by a laparoscopic instrument during surgical training. Infrared tracking of laparoscopic instruments is ineffective when real tissues attenuate the infrared signals. Incorporating the use of strain gauges for tip deflection measurements allows for online motion and load tracking during a procedure. Strain gauge voltages and infrared markers indicating displacement were both linear with respect to loads up to 700 grams. The resultant strain gauge voltage was equated to deflection values with a calibration constant. The results serve two purposes. First, it may enable the tracking and analysis of the skill level of novice surgeons using bench models. Second, the mechanical model of each instrument can be quantified and incorporated into virtual simulations, thus increasing model fidelity, effectively leading to better learning.

Surface exploration using laparoscopic surgical instruments: the perception of surface roughness

During laparoscopic surgery video images are used to guide the movements of the hand and instruments, and objects in the operating field often obscure these images. Thus, surgeons often rely heavily on tactile information (sense of touch) to help guide their movements. It is important to understand how tactile perception is affected when using laparoscopic instruments, since many surgical judgements are based on how a tissue 'feels' to the surgeon, particularly in situations where visual inputs are degraded. Twelve naïve participants used either their index finger or a laparoscopic instrument to explore sandpaper surfaces of various grits (60, 100, 150 and 220). These movements were generated with either vision or no vision. Participants were asked to estimate the roughness of the surfaces they explored. The normal and tangential forces of either the finger or instrument on the sandpaper surfaces were measured. Results showed that participants were able to judge the roughness of the sandpaper surfaces when using both the finger and the instrument. However, post hoc comparisons showed that perceptual judgements of surface texture were altered in the no vision condition compared to the vision condition. This was also the case when using the instrument, compared to the judgements provided when exploring with the finger. This highlights the importance of the completeness of the video images during laparoscopic surgery. More normal and tangential force was used when exploring the surfaces with the finger as opposed to the instrument. This was probably an attempt to increase the contact area of the fingertip to maximize tactile input. With the instrument, texture was probably sensed through vibrations of the instrument in the hand. Applications of the findings lie in the field of laparoscopic surgery simulation techniques and tactile perception.

The temporal organization of hand, eye, and head movements during reaching and pointing

Two experiments are reported that address the issue of coordination of the eyes, head, and hand during reaching and pointing. Movement initiation of the eyes, head, and hand were monitored in order to make inferences about the type of movement control used. In the first experiment, when subjects pointed with the finger to predictable or unpredictable locations marked by the appearance of a light, no differences between head and eye movement initiation were found. In the second experiment, when subjects pointed very fast with the finger, the head started to move before the eyes did. Conversely, when subjects pointed accurately, and thus more slowly, with the finger, the eyes started to move first, followed by the head and finger. When subjects were instructed to point to the same visual target only with their eyes and head, both fast and accurately, however, eye movement always started before head movement, regardless of speed-accuracy instructions. These results indicate that the behavior of the eye and head system can be altered by introducing arm movements. This, along with the variable movement initiation patterns, contradicts the idea that the eye, head, and hand system is controlled by a single motor program. The time of movement termination was also monitored, and across both experiments, the eyes always reached the target first, followed by the finger, and then the head. This finding suggests that movement termination patterns may be a fundamental control variable.

The coordination of hand transport and grasp formation during single- and double-perturbed human prehension movements

We investigated the mechanisms underlying human prehension movements, by perturbing the size and position of virtual targets. Subjects grasped virtual target discs with thumb and index finger. In 25% of trials, target size or position (single perturbation), or both (double perturbation) were changed 300 ms after target appearance. The experiments were designed such that the kinematic profiles of grasp formation and hand transport had a similar shape, and were analysed by the same algorithm. We found that grasp kinematics were influenced by changes of target position, and transport kinematics by changes of target size; we also found that the kinematics of double-perturbation trials could not be explained as a linear combination of single-perturbation effects. These findings confirm and expand previous evidence against the view that grasp and transport are controlled by fully independent channels. Most importantly, we found that the time of correction onset was not the same for grasp and transport, neither in single- nor in double-perturbation trials. This outcome argues against a holistic (single-channel) model of prehension; instead, our data are consistent with the notion of two mutually coupled channels.

What causes specificity of practice in a manual aiming movement: vision dominance or transformation errors?

The withdrawal of vision of the arm during a manual aiming task has been found to result in a large increase in aiming error, regardless of the amount of practice in normal vision before its withdrawal. In the present study, the authors investigated whether the increase in error reflects the domination of visual afferent information over the movement representation developed during practice to the detriment of other sources of afferent information or whether it reflects only transformation errors of the location of the target from an allocentric to an egocentric frame of reference. Participants (N = 40) performed aiming movements with their dominant or nondominant arm in a full-vision or target- only condition. The results of the present experiment supported both of those hypotheses. The data indicated that practice does not eliminate the need for visual information for optimizing movement accuracy and that learning is specific to the source or sources of afferent information more likely to ensure optimal accuracy during practice. In addition, the results indicated that movement planning in an allocentric frame of reference might require simultaneous vision of the arm and the target. Finally, practice in a target-only condition, with knowledge of results, was found to improve recoding of the target in an egocentric frame of reference.

Control strategies when intercepting slowly moving targets

In 3 experiments, the authors investigated and described how individuals control manual interceptive movements to slowly moving targets. Participants (N = 8 in each experiment) used a computer mouse and a graphics tablet assembly to manually intercept targets moving across a computer screen toward a marked target zone. They moved the cursor so that it would arrive in the target zone simultaneously with the target. In Experiment 1, there was a range of target velocities, including some very slow targets. In Experiment 2, there were 2 movement distance conditions. Participants moved the cursor either the same distance as the target or twice as far. For both experiments, hand speed was found to be related to target speed, even for the very slowly moving targets and when the target-to-cursor distance ratios were altered, suggesting that participants may have used a strategy similar to tracking. To test that notion, in Experiment 3, the authors added a tracking task in which the participants tracked the target cursor into the target zone. Longer time was spent planning the interception movements; however, there was a longer time in deceleration for the tracking movements, suggesting that more visually guided trajectory updates were made in that condition. Thus, although participants scaled their interception movements to the cursor speed, they were using a different strategy than they used in tracking. It is proposed that during target interception, anticipatory mechanisms are used rather than the visual feedback mechanism used when tracking and when pointing to stationary targets.

The visuomotor system resists the horizontal-vertical illusion

The effect of the horizontal-vertical illusion on the visual and visuomotor systems was investigated. Participants (N = 8) viewed horizontal and vertical lines in an inverted-T stimulus and judged whether the two line segments were the same or different lengths. Participants also reached out and grasped either the vertical or the horizontal line segment of the stimulus. Perceptually, participants succumbed to the illusion; that is, they judged Ts of equal horizontal and vertical line lengths to be different and Ts of unequal line lengths to be the same. When reaching toward the same stimuli, however, the size of their grip aperture was scaled appropriately for the various line lengths. Thus, whereas the perceptual system succumbed to the illusion, the visuomotor system did not. Those results support a model proposed by M. A. Goodale and A. D. Milner (1992), who posited separate cortical pathways for visual perception and visually guided action.

The effect of illusory size on force production when grasping objects

Milner and Goodale (1995) have proposed that visuomotor and perceptual processes are mediated by discrete visual systems that reflect the functional independence of action and perception. The visuomotor system is proposed to be insensitive to pictorial illusions of object size, whereas the perceptual system is reliably "tricked" by such figures. Brenner and Smeets (1996) and Jackson and Shaw (2000) demonstrated that grasp preshaping, but not grasping force, is immune to the Ponzo visual illusion, suggesting that not all visuomotor processes operate independently of the perceptual system. The present study investigated the effect of illusory object size on prehension kinematics and grasping dynamics (i.e., grip force and load force) as well as perceptual judgements of object size. Unlike previous investigations, object mass was held constant independent of changes in size. The Ponzo figure reliably affected perceptual estimates of object size, but this effect was restricted to one form of the illusion. Some aspects of the prehension movement were sensitive to veridical but not illusory object size (peak grip aperture, peak grip force, peak vertical wrist acceleration), whereas other movement parameters demonstrated illusory size effects (movement time, peak wrist velocity). Still other movement parameters were not sensitive to veridical or illusory object size (peak load force). Together the data suggest that certain prehension components are immune to pictorial illusions of object size, whereas others are not. Complex interactions between the perceptual and visuomotor systems appear to underlie the anticipatory scaling of grasping forces in prehension.

Motor skill learning of concentric and eccentric isokinetic movements in older adults

Neuromuscular adaptation at the onset of resisted exercise can be observed as increases in torque and surface electromyography. The effect of learning the motor task has been hypothesized to contribute to these early increases, especially for older people. Thus, the purpose of this study was to investigate the facilitatory effects of practice on motor performance in older adults during short-term isokinetic training of the ankle dorsiflexors (DF). Twenty-eight men and women (M = 76.3 +/- 4.6 years) volunteered for a 2-week, 3-days/week strength training program. They were tested in a sitting position on a KinCom isokinetic dynamometer at 30, 90, and 180 degrees s-1 through 40 degrees of DF movement (concentric and eccentric contractions). Criterion curves of lever arm angle patterns were cross-correlated with subject-generated angle patterns, showing significantly better correlations on posttest versus baseline. Smoothness and proficiency of muscle contraction improved with practice by fewer hesitations in movement and increased ability to change between concentric and eccentric muscle contractions. Increased agonist electromyography and torque were hypothesized to be secondary to greater neural drive and/or synchronization of motor unit firing rate and/or recruitment during maximal voluntary contraction, improved coordination, and adapted neural control of concentric and eccentric muscle contraction.

Task dependent processing of visual information about target acceleration

The objective of this study was to investigate the sensitivity of the perceptual and motor systems to target acceleration information using verbal magnitude estimations of target acceleration and manual interception of these targets. The results showed that in the perceptual task the participants were responding mainly to acceleration threshold values, which is acceleration as a function of initial, final, and average velocities, rather then to the absolute accelerations. When manually intercepting the targets the participants responded mainly to the absolute acceleration value and target initial velocity. Thus, these results suggest that target motion can be processed in the ventral (perception) and dorsal (action) visual streams however different motion characteristics are processed in these streams depending on the required output.

Target velocity effects on manual interception kinematics

Participants generated manual interception movements toward a target cursor that moved across a computer screen. The target reached its peak velocity either during the first third, at the midpoint, or during the last third of the movement. In Experiment 1 the view of the target was available for either the first 316, 633, 950, or 1267 ms, after which it disappeared. Results showed that for all viewing conditions, the timing of the interception velocity was related to the temporal properties of the target's trajectory. In Experiment 2, when the portion of the target trajectory that was viewed was reversed (such that participants did not see the first 316, 633, 950, or 1267 ms of the trajectory, but instead saw only the later portions of the trajectory), there was no clear relationship between the target trajectory and the timing of the aiming trajectory. These results suggest that participants use visual information early in the target's trajectory to form a representation of the target motion that is used to facilitate manual interception.

Target viewing time and velocity effects on prehension

The goal of the present study was to understand which characteristics (movement time or velocity) of target motion are important in the control and coordination of the transport and grasp-preshape components of prehensile movements during an interception task. Subjects were required to reach toward, grasp and lift an object as it entered a target area. Targets approached along a track at four velocities (500, 750, 1000 and 1250 mm/s) which were presented in two conditions. In the distance-controlled condition, targets moving at all velocities traveled the same distance. In the viewing-time-controlled condition, combinations of velocity and starting distances were performed such that the moving target was visible for 1000 ms for all trials. Analyses of kinematic data revealed that when, target distance was controlled, velocity affected all transport-dependent measures; however, when viewing time was controlled, these dependent measures were no longer affected by target velocity. Thus, the use of velocity information was limited in the viewing-time-controlled condition, and subjects used other information, such as target movement time, when generating the transport component of the prehensile movement. For the grasp-preshape component, both peak aperture and peak-aperture velocity increased as target velocity increased, regardless of condition, indicating that target velocity was used to control the spatial aspects of aperture formation. However, the timing of peak aperture was affected by target velocity in the distance-controlled condition, but not in the viewing-time-controlled condition. These results provide evidence for the autonomous generation of the spatial and temporal aspects of grasp preshape. Thus, an independence between the transport and grasp-preshape phases was found, whereby the use of target velocity as a source of information for generating the transport component was limited; however, target velocity was an important source of information in the grasp-preshape phase.

Manual asymmetries in response to rapid target movement

Two studies are reported that examine reaching responses of the two hands to unexpectedly displaced targets, located along the midline and to the left and right. In the first study, subjects used the index finger to point to the targets. The left hand movement time and time to peak velocity were longer than for the right hand. For both hands, performance was superior when reaching into ipsilateral space. No evidence was found for early (before peak velocity) trajectory corrections in response to perturbations. In the second study, subjects reached and grasped dowels which appeared to move unexpectedly. Again, movement times were smaller when reaching with the right hand when compared to the left, but only on trials when the dowel was located on the subject's right. When subjects reached to the left, the left hand had shorter movement times. Early trajectory corrections were observed in the velocity profiles; the pattern was similar for both hands. These data are discussed in terms of visual processing abilities of the left and right cerebral hemispheres, and visual processing abilities when pointing and grasping.

The influence of aging and target motion on the control of prehension

The purpose of this study was to examine age-related differences in reaching behavior when younger (mean age = 26.0 years) and older (mean age = 70.1 years) individuals were required to reach toward and grasp both small and large targets that were either stationary or moving. The older subjects had shorter movement times, and smaller within-subject movement time variability than younger subjects. Also, the deceleration of the reach was shorter for older subjects, indicating that they were not making extensive use of on-line feedback, and were instead utilizing anticipatory control strategies. There were no age differences in the size of the maximum grasp around the target, but the timing of the grasp was influenced by target motion for the younger subjects, suggesting on-line control for the younger subjects only.

Anticipatory locomotor adjustments for accommodating versus avoiding level changes in humans

The control of locomotion has been studied from various perspectives related to the tasks of pattern generation, equilibrium control or adaptation to the environment. The last of these locomotor components has received comparably less attention, specifically pertaining to anticipatory adjustments. Continuing the work which has been conducted on both humans and cats, the present paper explores the nature of the differences in anticipatory locomotor adjustments for obstacle avoidance versus the accommodation to level changes. Six subjects walked in six different environments including no obstructions, a simple obstacle, two different level changes (a platform and stairs), and a combination of an obstacle with each respective level change. Full dynamic analyses allowed comparison of muscle torques as well as muscle power generated and absorbed at the lower limb joints across conditions. It was found that the previously shown robust lower limb reorganization characterized by a knee flexor generation strategy was upheld in all conditions when the obstacle was present. Pure level changes involved an augmentation of the ongoing hip strategy inherent in normal level walking. In the compound environment of obstructed level changes, subjects chose to combine an augmentation of hip flexor power with a reorganization to active knee flexion. The results are discussed from the point of view of general principles of mechanical coordination and the exploitation of intersegmental dynamics for foot transport.

An investigation into movement planning and execution deficits in individuals with schizophrenia

The purpose of this study was to examine whether individuals with schizophrenia demonstrate slowing in movement planning (reaction time), or in movement execution (movement time and velocity), in comparison to normals. Twelve schizophrenic and 12 control right-handed males performed aiming movements with a mouse (controlled by either the left or right hand) on a graphics tablet towards targets of differing sizes and distances appearing on a computer screen. Results showed that, for reaction time, the controls were faster than the schizophrenics and the latter had a left hand advantage for movement preparation while the controls showed no such differences. For movement time, no group differences were found. However, as expected, movement times were shorter (i.e., movements were faster) to the large, and near targets. These results support Fitts' law (Fitts, 1954) which describes a relationship where aiming movement time decreases as target distance decreases, and target size increases. We provide evidence here for a movement planning deficit in schizophrenic patients with no decrement in movement execution compared to controls.

Delayed visual feedback while learning to track a moving target

Two studies investigated the effects of delayed visual feedback on manual tracking. In Experiment 1, individuals practiced with visual feedback provided either immediately (0 delay) or with a 333-ms delay. During acquisition, the 0 delay group performed with less error than the 333-ms delay group. A retention test with 0 delay feedback was performed with the least error by the 0 delay group. A transfer test using a different 0 delay tracking pattern, was performed with the least error by the 333-ms delay group. In Experiment 2, individuals practiced at six different delays. Error increased as training feedback delay increased. For retention there were no differences between the delay groups during the 0 delay retention. At a 417-ms retention, test error decreased as training feedback delay increased. Results indicate that error during acquisition does not necessarily impair learning and that feedback delays can be beneficial for learning.

The influence of summary knowledge of results and aging on motor learning

This study examined whether older adults (mean age = 75.0 years) use summary knowledge of results (KR) to facilitate learning in a manner similar to that of young adults (mean age = 22.5 years). All subjects were required to learn a computer-key-pressing task in a specified goal time. During acquisition, subjects received either KR after every trial, or summary KR. All subjects then performed no-KR retention trials. In acquisition, KR after every trial facilitated timing accuracy for both the younger and older groups in comparison to the summary KR groups. The young subjects were equally variable in both KR practice groups. For older subjects summary KR facilitated more consistent performance. In retention, the summary groups were more accurate than those subjects who received KR after every trial. There were no accuracy or variability differences between the two age groups during retention. These results suggest that older adults are able to use summary KR to facilitate learning in a manner similar to that of young adults.

Visuomotor control when reaching toward and grasping moving targets

Two experiments were conducted to examine the influence of target motion on the control and coordination of reaching and grasping movements. In Experiment 1 all the measures which reflected the transport or reaching phase of prehension (movement time, peak velocity, time to peak velocity, and transport tau margin) were sensitive to the velocity of the target, with subjects moving even slower than during the stationary trials, when the target was moving very slowly. Measures which reflected grasp formation such as the size of maximum aperture and the grasping tau margin were not influenced by target speed. To further investigate this dissociation between grasp and transport, different object sizes and even slower object speeds were introduced in Experiment 2. Transport results similar to those found in the first study were observed. However, in Experiment 2, both size of peak aperture and the grasping tau margin were sensitive to target movement. The results of these two studies are discussed in terms of the limitations of optic variables in the visual regulation of movement, and the independence of control of the reach and grasp phase of prehension.

Influence of object size on prehension in leukotomized and unleukotomized individuals with schizophrenia

The aim of this study was to investigate the influence of schizophrenia and frontal leukotomy on the control and perceptual-motor coordination of reaching and grasping movements. Reaches to various-sized drinking glasses were videotaped for unleukotomized and leukotomized adults with schizophrenia, and for healthy age-matched controls. Kinematic analyses showed that while the two patient groups moved more slowly than the controls, the proportion of overall movement time spent accelerating to reach peak velocity and the proportion of overall movement time spent decelerating before contact with the glasses was similar for all three groups. For grasp formation, the two patient groups, which did not differ, opened their hands wider than did the controls; however, all three groups opened their hands to the appropriate size in response to the various glass sizes. The frontal lesions of the leukotomized patients were not related to motor control deficits when compared to the control schizophrenic patients. As well, the perceptual abilities of the patients were adequate as evidenced by their ability to scale their grasp to glass size.

Proprioception during manual aiming in individuals with shoulder instability and controls

Recurrent glenohumeral joint instability is a common orthopaedic problem. One possible cause of this repeated instability is a lack of neuromuscular control and kinaesthetic sense of the glenohumeral joint. The purpose of this study was to determine whether there is a deficit in joint proprioception in subjects with recurrent anterior glenohumeral instability as compared with individuals with no previous shoulder pathology. Subjects were asked to generate pointing movements with their uninjured limb and to match this limb position with the injured limb. Movements of the pointing limb were measured with an optoelectric three-dimensional movement analysis system. These movements were performed in three conditions: 1) with full vision, 2) without vision, and 3) without vision with vibration to the posterior deltoid muscle. For the temporal and spatial measures, there were no significant differences between the control and shoulder instability groups. However, the kinematic data describing arm trajectory formation showed a performance decrement in the no vision with vibration condition for the subjects in the shoulder instability group, suggesting that they suffer from a proprioceptive deficit.

Manual performance in leukotomized and unleukotomized individuals with schizophrenia

Seven leukotomized adults with schizophrenia (LS), eight unleukotomized adults with schizophrenia (ULS), and eight healthy control (C) individuals were required to reach toward and grasp a small object that was either stationary or moving. Reflective markers were placed on the subject's index finger, thumb and wrist, and movements were videotaped. As expected the LS and ULS groups moved slower than the C group when the target was stationary. However, when the target was moving, all three groups moved faster, with the LS and C groups having the same movement times, and the ULS group having the fastest movement time. When the timing of the reaching trajectory was assessed, the LS group spent less time decelerating and closing their hands around the object, indicating their movements were controlled with less precision. When grasp formation was analyzed, for the stationary condition, the maximum apertures of the LS and ULS groups were not different, and both were larger than those of the C group. For the moving target condition, aperture increased for all groups but was smallest for the C group, intermediate for the LS group and largest for the S group. There was actually less within subject variability in peak aperture and maximum aperture closing speed for the LS and ULS groups in comparison to the C group, perhaps indicating a limited repertoire of potential motor responses for the patient groups. These results suggest that individuals with schizophrenia are able to use redundant information as well as controls, and that leukotomized individuals with schizophrenia have greater motor control deficits than unleukotomized schizophrenics.

A preliminary analysis of the coordination of reaching, grasping, and walking

The purpose of this investigation was to describe the strategies used by individuals when motor systems controlling locomotion and prehension must be used simultaneously to perform a task. Subjects were required to perform five tasks: walk normally, walk and pick up a small object, walk and pick up a large object, pick up a small object from a stationary standing position, and pick up a large object while standing. The grasping and walking movements were videotaped and the frequencies of various behaviors were observed (type of grasp, location of contact with the object, support leg during contact with the object, timing of gaze toward object). Characteristics of the grasp were influenced by object size, not by whether the subject was walking. Gaze was shifted to the object before initiation of reach and this pattern was not influenced by size of the object or movement of the subject. Finally, subjects preferred using an ipsilateral support leg while generating the reach, which is a deviation from normal gait patterns. Findings indicate that the motor control system may be hierarchically organized in such a way that stability of the lower limbs supersedes the control of the movement patterns of an upper limb.

Relationship between movement planning and psychopathology profiles in schizophrenia

BACKGROUND

There has been evidence that psychopathology in schizophrenia consists of three separable syndromes: reality distortion, disorganisation, and psychomotor poverty. The objective of this study was to explore the relationship between planning and execution of movement and each of the syndromes in schizophrenia.

METHOD

Twenty-one right handed DSM-III-R schizophrenic patients performed a total of 80 trials of a motor movement task, varying distance of movement x size of the target x hand. Times taken to plan the movement (RT) and to carry it out (MT) were examined for their relationship with contemporaneous as well as lifetime profiles of the three syndromes in schizophrenia.

RESULTS

Significant correlations are reported between RT and current as well as lifetime measures of disorganisation syndrome. Somewhat weaker correlations are reported between RT and psychomotor poverty, but only for the right-handed tasks. Partial correlations suggest that the influence of neuroleptic medication explains all but one of the correlations between psychomotor poverty and RT, but does not account for the relationship between disorganisation and RT. No other relationship emerged between any of the movement and symptom measures.

CONCLUSIONS

These findings indicate that dysfunction in movement planning is related primarily to concurrent disorganisation, as well as to the prominence of disorganisation over the patient's history.

Effects of schizophrenia and prefrontal leukotomy on movement preparation and generation

The purpose of this study was to investigate the ability of leukotomized and unleukotomized schizophrenic patients to use advance information in the process of movement preparation. Subjects participated in an aiming task in which movements could be defined on the basis of hand used to perform the task, and distance travelled to the target. Subjects were provided with full, partial, or no prior information about the upcoming movement by either precueing hand, distance, both hand and distance, or by providing no precue. The leukotomized and unleukotomized schizophrenic patients were able to use this advance information to facilitate the speed of their responses in much the same way as did subjects in a normal control group. These results are discussed in terms of models of movement preparation, and the role of the frontal lobes in schizophrenia and movement planning.

On the Role of Knowledge of Results in Motor Learning

Recent work on the role of knowledge of results (KR) in motor learning has challenged some traditional assumptions. In particular, the guidance hypothesis suggests that there is a detriment to learning when KR guides the learner toward correct performance. Three experiments that explored this hypothesis are reported here. These experiments contrasted the effects of relative frequency of guidance versus the relative frequency of KR. According to the guidance hypothesis, it was predicted that parallel effects of the relative frequency manipulation on motor learning and performance would result under guided and KR conditions. The movement task was a reciprocal timing task that was either paced by a metronome (Experiment 1) or augmented by auditory KR (Experiments 2 and 3). The results of Experiments 1 and 3 revealed a number of parallel effects, thus providing support for the guidance hypothesis. The contrast of Experiments 1 and 2 resulted in a number of dissociable effects, however. These findings are discussed in relation to the potential guiding properties of KR and their impact on motor performance and learning.

A Note on the Relationship Between Task Requirements and the Contextual Interference Effect

Typically, tasks used in past contextual interference experiments had movement, spatial pattern, or timing requirements. The possibility exists that the blocked/random manipulation of only one of these task characteristics contributes to the contextual interference effect. The purpose of the experiment reported here was to test the impact of separate movement and timing tasks on the superior learning of random trained groups. The task for all subjects in the movement condition was to release a start button and knock over a wooden barrier. There were three movement goals to be learned. Half of the subjects in this condition practiced the three movements in a blocked schedule and half practiced them in a random schedule. The subjects in the no-movement condition estimated the same three times by holding down the start button for the appropriate duration. Similarly, these subjects were divided into random and blocked practice groups. All subjects then performed a retention test. Results showed that for the movement condition, the blocked group performed with less error than the random group during acquisition. In retention, however, the random group performed with less error than the blocked group. conversely, for the no-movement condition, there were no differences between the two practice schedule groups during acquisition or during retention for any of the dependent measures. These results indicated that experimental tasks must have some type of movement requirement in order to facilitate learning through the use of random practice schedules.

Training for Transfer of a Movement Timing Skill

Previous findings by Langley and Zelaznik (1984) suggested two hypotheses why segmental (phasing) timing training produced a more superior transfer than nonsegmental (duration) timing training. One view (the higher order variable hypothesis) suggested that segmental training developed a timing skill that was flexible for various types of transfer tasks. Another view (the contextual interference hypothesis) was that the difficulty associated with segmental training was sufficient to provide this flexibility for later transfer. The present study contrasted these hypotheses by comparing transfer following phasing or duration training but which was low in contextual interference. The acquisition results favor a contextual interference explanation. The transfer results, however, are clearly a function of the development of a higher order timing skill. These findings are discussed in terms of the development of a timing skill that is best suited for flexibility of transfer.

Cerebral specialization in young adults with Down syndrome

Adults with and without Down syndrome performed a rapid unimanual finger-tapping task alone and while sound-shadowing high frequency words. For male subjects, the concurrent speech disrupted right-hand, but not left-hand performance. Females suffered finger-tapping decrements in both hands in the dual-task situation. These results provide no evidence for reverse (right hemisphere) lateralization of speech in individuals with Down syndrome.

Pedal asymmetry in the reproduction of spatial locations

Roy and MacKenzie (1978) showed that the left thumb is superior to the right thumb in reproducing a spatial location. This study replicated and extended their findings to the reproduction of spatial locations by the feet. We attribute the left foot advantage in this study to the superiority of the right hemisphere in processing spatial information.

Dual-task interference between speaking and listening and a unipedal force production task

Twenty-four male right-handed adults performed a force production task with their right and left feet alone, and while sound-shadowing or listening to high frequency words. Overall, subjects performed better with their left foot than their right foot. Further, sound-shadowing, but not listening disrupted right foot performance. The concurrent language tasks had no effect on left foot performance.