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Biomedical subjects

A Vinter

Publications and source records attributed to A Vinter.

10 recordsLinked to original sources
PubMed1999

Isolating unconscious influences: the neutral parameter procedure.

Earlier demonstrations of unconscious learning have been regularly challenged. In this paper, we suggest that earlier demonstrations were not compelling due to certain properties of the experimental situations, and notably that conscious exploitation of explicit knowledge, if present, would coincide or conflict with the results of unconscious processing. We designed a method consisting of inducing a neutral behavioural change in the way subjects drew geometric figures. Two experiments showed that important and long-lasting modifications of drawing behaviour were obtained following specially devised practice, although these modifications could not be expected from deliberate adaptive strategies. In addition, we showed that subjects were unaware of the manipulation to which they had been exposed. The study provides striking evidence for unconscious learning and offers insights for the design of suitable new tools to investigate unconscious cognition.

Adolescent↗
PubMed1998

The representation of gravitational force during drawing movements of the arm.

The purpose of the present experiment was to study the way in which the central nervous system (CNS) represents gravitational force (GF) during vertical drawing movements of the arm. Movements in four different directions: (a) upward vertical (0 degrees), (b) upward oblique (45 degrees), (c) downward vertical (180 degrees) and (d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by nine subjects. Data analysis focused upon arm movement kinematics in the frontal plane and gravitational torques (GTs) exerted around the shoulder joint. Regardless of movement direction, subjects showed straight-line paths for both speed conditions. In addition, movement time and peak velocity were not affected by movement direction and consequently changes in GT, for both speeds tested. Movement timing (evaluated through the ratio of acceleration time to total time) changed significantly, however, as a function of movement direction and speed. Upward movements showed shorter acceleration times when compared with downward movements. Concerning the four directions, movements made at 0 degrees and 45 degrees differed significantly from those made at 135 degrees and 180 degrees. Drawing movements executed at rapid speed presented similar acceleration and deceleration times compared with movements executed at normal speed, which showed greater acceleration than deceleration times. In addition, the form of velocity profiles (assessed through the ratio of maximum to mean velocities), was significantly modified only with movement speed. Results from the present study suggest that GF is efficiently incorporated into internal dynamic models that the brain builds up for the execution of arm movements. Furthermore, it seems that GF not only is a mechanical parameter to be overcome by the motor system but also constitutes a reference (vertical direction), both of which are represented by the CNS during inverse kinematic and dynamic processes.

Adult↗
PubMed1998

Exploitation of elasticity in copying geometrical patterns: the role of age, movement amplitude, and limb-segment involvement.

An experiment is reported in which 12 adults and 12 10-year-old children copied three-segment geometrical patterns under various size and limb-segment involvement instructions. Next to an assessment of movement pauses, analyses of pen-tip displacements focused on: (1) the accuracy of size reproduction, (2) movement time, and (3) ratio of peak-over-mean velocity. A low value of the latter measure was considered to reflect the adoption of a cyclical movement regime facilitating the exploitation of elastic properties of muscles and tendons during execution. Subjects generally produced size overshoots which, particularly for the children, were most pronounced for small patterns. These effects were accompanied by prolonged movement times. Peak-over-mean velocity ratios were smallest in adults, in large patterns, and when the arm instead of the hand was required as effector. Although adults paused more frequently than children, pause durations were similar in both groups. It is suggested that fast movements with low peak-over-mean velocity ratios reflect successful attempts by subjects to exploit the elasticity of muscles and tendons. These attempts are accompanied in the present task, however, by an increased risk of having to pause between subsequent segments of a movement sequence, possibly for energy-dissipation reasons.

Adult↗
PubMed1998

Spatial features of angular drawing movements in Parkinson's disease patients.

The present study shows that drawings from Parkinson's disease (PD) patients display specific spatial features when compared to those produced by age-matched controls. Their drawings are globally smaller, or more precisely, the larger the requested size, the greater the size reduction. PD subjects have also more difficulties in producing obtuse than acute angles: angles of obtuse patterns are shrinking and their segment lengths are shortened. This could be due to the fact that an obtuse angle brings the effector joints close to the limits of their functional ranges of motion, which may be reduced in PD patients. Results related to segment direction show that PD patients are globally more imprecise than controls in the production of movement directions, but perform nevertheless relatively well for horizontals and verticals drawn in preferred directions. These results are referred to two contradictory models relating movement direction to the type of movement coordination involved.

Aged↗
PubMed1998

[Drawing movements and gravitational force: central or peripheral regulation?].

Drawing arm movements in four different directions: a) upward vertical (0 degree), b) upward oblique (45 degrees), c) downward vertical (180 degrees) and d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by eight subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon pen kinematics in the frontal plane. Velocity profiles were unimodal for all conditions. The ratio of acceleration time to total movement time changed significantly as a function of the direction and the speed of the movement. Movement time and was not affected by movement direction and consequently changes in gravitational torques, for both speeds tested. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravitational force.

Adult↗
PubMed1996

Biomechanical and perceptual determinants of drawing angles.

This study focuses on perceptual and biomechanical determinants of the kinematics of angular drawing movements. Two experiments are reported in which twelve righthanded adults were asked to draw geometrical patterns consisting of three segments comprising either two acute or two obtuse angles. In Experiment 1, a lower frequency of pauses was observed in acute patterns and their segment length tended to be overestimated. The former effect is attributed to the exploitation of elasticity (Guiard, 1993). In order to evaluate whether the latter effect was due to perceptual factors, a second experiment was conducted. Twelve subjects drew a subset of the angular patterns under normal visual conditions and under conditions in which they could neither see their moving limb nor the resulting drawing trace. Again, subjects produced more pauses at obtuse than at acute angles and tended to overestimate the segment length in acute patterns. It is concluded that pauses are likely to occur between segments of discrete movement sequences when potential energy needs to be dissipated. When conditions arise that allow subjects to exploit elasticity, however, segment length tends to increase. The results of Experiment 2 confirm that these phenomena are independent from visual perception.

Adult↗
PubMed1993

Sensorimotor development in cerebral-palsied infants assessed with the Uzgiris-Hunt scales.

The cognitive development of a group of 89 cerebral-palsied infants, aged six to 24 months, was investigated using the Uzgiris-Hunt scales. The results were compared with normative data for the Italian population and with data obtained in a group of low-risk term and preterm infants, 11 to 13 months old. The test was easy to carry out, even on infants with a severe motor impairment. The majority of the infants showed cognitive delay on most of the scales. Tetraplegic patients performed significantly worse than those with diplegia or hemiplegia. There were no differences between preterm and term infants, for either normal or cerebral palsy groups, if age was corrected for preterm birth. Sensorimotor development appeared to be organized similarly for cerebral-palsied infants and normal controls; however, these data raise the question of the role of action in early cognitive development.

Cerebral Palsy↗
PubMed1983

Accuracy and stability of self-image of mentally retarded adults.

The accuracy and stability of self-image of 21 mentally retarded adults and 24 nonretarded adults were studied. The subjects were confronted with a distorting mirror that made their faces look either fatter or slimmer. Results showed that retarded adults saw themselves as more distorted than did non-retarded adults. Significant sex differences in the retarded population were found. Both the precision and the stability of retarded adults' self-image were significantly correlated with IQ. Results were interpreted within a cognitive framework.

Adult↗
PubMedDate not supplied

Implicit learning in children is not related to age: evidence from drawing behavior.

Three experiments are reported on implicit learning in 432 children between the ages of 4 and 10 years, using a new paradigm ("the neutral parameter procedure") based on drawing behavior. The first two experiments demonstrated that children modified their drawing behavior following specially devised practice in such a way that these modifications could not be viewed as the result of deliberate adaptive strategies. The third experiment showed that these behavioral modifications lasted for at least 1 hr after the training phase. No age-related differences appeared in the experiments. A comparison of children's data with similar adults' data also failed to reveal any age differences. These results provide compelling evidence that implicit learning processes are age independent. Some implications of these results for developmental issues are discussed, notably the hypothesis of the formation of implicit knowledge in the course of learning.

Aging↗