Control theories in motor behavior

Temporal and spatial characteristics in repetitive movement

The question addressed is whether temporal or spatial characteristics of a movement sequence are represented in a motor program. Subjects executed one to five straight-line strokes as fast as possible on a digitizing tablet. The duration and length of each stroke were computed and intercorrelated. Nineteen out of 20 possible correlations were significant for length per stroke data while only one of the 20 correlations was significant for duration. Further, performance data on the five stroke patterns were sorted to examine whether the first stroke determined the overall temporal/spatial pattern of the subsequent strokes executed. It was found that only sorting by length of the first stroke produced different subsets of movement patterns. These results are argued to be in support of the hypothesis that the spatial microstructure is controlled in a prepared movement sequence.

Limb segment inclination sense in proprioception

Two experiments were performed to determine if proprioceptive signals are perceived more readily in terms of limb segment inclinations to the vertical than as joint angles. Subjects attempted to match arm positions with the upper arms supported at different inclinations. Constant error data showed that, when instructed to match forearm inclinations to the vertical, subjects were very accurate. When required to match elbow joint angles, however, errors were strongly biased in the direction of matching forearm inclinations. The results support a view of proprioception as a system in which afferent signals related to the gravitational torques acting at joints lead to the perception of limb orientation rather than joint angles. Such a system would allow more efficient determination of the relationship of limb segments to external objects than would one based purely on joint angles.

Relation of spelling and writing in learning disabilities

The paper describes a study in which the relationship between the cognitive and psychomotor aspects of children's spelling and writing performances was investigated. By comparing data from various categories of children the relationship between the semantic and psychomotor functions could be examined, and differences between the skill performances of the three groups of students were predicted. A four-way 3 X 3 X 2 X 2 orthogonal design with categories of subjects, type, structure, and length of task as independent variables was used in the laboratory study, with 24 "normal", 24 dyslexic, and 24 dysgraphic nine-year-old children as subjects. Most of the 16 hypotheses were verified by data identifying some of the spelling and writing characteristics of the three groups of children and the effects of contextual parameters on their performances. Dyslexic children, for example, seemed to write more slowly than the others, and their mean score of spelling errors was the highest one, whereas the dysgraphic children had the lowest mean score in writing accuracy and rhythm.