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Biomedical subjects

H Carnahan

Publications and source records attributed to H Carnahan.

17 recordsLinked to original sources
PubMed1998

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.

Hand↗
PubMed1997

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.

Adult↗
PubMed1997

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.

Accommodation, Ocular↗
PubMed1996

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.

Acceleration↗
PubMed1996

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.

Aged↗
PubMed1996

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.

Adult↗
PubMed1996

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.

Analysis of Variance↗
PubMed1996

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.

Adult↗
PubMed1995

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.

Adult↗
PubMed1995

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.

Adult↗
PubMed1995

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.

Adult↗
PubMed1994

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.

Aged↗
PubMed1987

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.

Adult↗
PubMed1987

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.

Adolescent↗
PubMed1986

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.

Dominance, Cerebral↗
PubMedDate not supplied

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.

Adult↗