Biomedical subjects

G Stelmach

Publications and source records attributed to G Stelmach.

5 recordsLinked to original sources

PubMed1999

Temporal and spatial relationship between reaching and grasping. Commentary on "A new view on grasping".

Smeets and Brenner propose a model that attempts to account for the action patterns involved in prehensile behaviors. However, the model does not provide a full account of the available data on temporal and spatial relationships between the transport and grasp components. Predictions from the model in its current form appear to correspond only to experimental results in a very general way.

Feedback↗

PubMed1995

Altered force release control in Parkinson's disease.

Isometric force tracking and force aiming modified by visual feed-back was investigated in Parkinsonian (PD) and control subjects. Production and maintenance of isometric force, production and release of isotonic force, and maximum force were tested. Statistical analysis revealed that the PD patients could perform most force tasks in a similar manner to that of control subjects. However, PD patients had difficulties in sustaining target force over a 30-s period and in performing rapid alternating movements. The major finding in PD patients was an inability to precisely release a target force. Overall these data suggest that the release of a produced force is a sensitive motor control parameter in Parkinson's disease.

Adult↗

PubMed1994

The effect of viewing the static hand prior to movement onset on pointing kinematics and variability.

Pointing accuracy and arm movement kinematics of six human subjects were measured in three conditions where the hand was never visible during the ongoing movement: (1) in the dark; (2) the static hand was seen in peripheral vision prior to target presentation, but not during the reaction time (H-T); (3) the static hand was seen in peripheral vision until movement onset (H+T). It was shown that: (1) viewing the hand prior to movement decreased pointing variability as compared to the dark condition. (2) Viewing simultaneously hand and target (H+T) and further decreased pointing variability as compared to the H-T condition. This effect was proportional to the reaction time. (3) A lengthening of the deceleration phase was observed for movements performed in the H+T condition, as compared to the other two conditions. (4) A negative correlation between variability and the first part of the deceleration phase was observed in the H+T condition, but neither in the H-T condition nor in the dark. These results suggest that the decrease in pointing variability observed in the H+T condition is due to a feedback based on kinesthetic reafference. Better encoding of the initial position of the hand relative to the target (as in H+T) would allow a calibration of arm position sense, which is used to drive the hand toward the target during the deceleration phase.

Adult↗

PubMed1991

Direction and amplitude precuing has no effect on automatic posture responses.

Automatic postural responses of leg muscles to the sudden displacement of standing support were investigated under four different conditions of information given to subjects in advance. Results from three groups of subjects were compared: 6 normal subjects, 10 patients with cerebellar disease, and 9 patients with Parkinson's disease. Specifically, each subject was provided with visual information about the direction and/or the amplitude of an upcoming platform tilt. For the control situation no advance information on the characteristics of platform tilt was provided. Neither the latencies nor the integrals of postural EMG-responses showed alterations with advance information. In contrast, in a control experiment in which 3 normal subjects had to perform large or small forward or backward voluntary movements of the body around the ankle joint, shorter onset-latencies of leg muscle EMG responses were observed with increasing complexity of the advance information. These results suggest that, unlike voluntary movements, postural responses to rapid surface tilts do not benefit from advance visual information on direction or amplitude of a postural disturbance.

Adult↗

PubMed1983

Localization without content. A tactile analogue of 'blind sight'.

We examined the ability of a patient, who had a cerebral lesion involving the left posterior hemisphere, to identify and to localize stimuli applied to her "deafferented" right upper limb. We observed a functional dissociation between localization and identification in both performance and subjective report. This finding may be a tactual analogue of "blind sight."

Afferent Pathways↗