No abstract

In Experiment 1, subjects were supplied with prior information about 1, 2 or all dimensions (the active hand, direction, and extent) of a pointing movement. RTs showed that dimeasional effects were found in highly compatible stimulus-response conditions, dimensions speeificafioa times were underadditive, and the difference in RT between dimension values when that dimension remained to be specified, disaplaeared when the dimension was precued. In Eximrimeat 2, subjects were required to name target color after a set of colored targets was presented as a precue, and dimensional effects disappeared. In Experiment 3, a target was presented as a prime, followed by presentation of either the same or a different target. As compared to Experiment l, dimensional effects were amplified. In conclusion, when two or more movement dimensions have to be specified simultaneously, dimension values are independently selected, then integrated in a compound programming operation. The fact that actions must be spatially and temporally ordered to reach their goal has indicated that movements are precisely planned before execution. Consequently, the concept of the motor "program" remains one of the most influential in the field of motor control studies (Paillard, 1960; Requin, Semjen, & Bonnet, 1984). In the early and most popular conception (cf. Keele, 1968), the motor program is said to be formed by a set of "instructions" specifying the spatial and dynamic parameters of a movement. These instructions are selected in some motor register according to both the initial state of the muscular system and the action purpose. Then they are assembled to construct the program. These are translated finally into a set of orders addressed to the peripheral effectors, that determine the biomechanical characteristics and, therefore, the kinematics of the movement performed. Such a conception, which can be called parametric, has been increasingly challenged during the last few years (cf. Kelso, 1981) along three lines. First, the idea that every different movement is controlled by a specific program implies an unlimited span of the instructions register. Revised and more abstract conceptions of motor programming were therefore proposed by distinguishing at least two hierarchically organized levels in the central processes responsible for movement organization. At the highest level only a limited number of programs are stored, as "generalized entities" (Schmidt,

Abnormal clumsiness was investigated within the framework of an information processing model using chronometric techniques. Eight clumsy and eight normal children were tested in two experiments in which between-group comparisons were made of the functioning of the perceptual and response selection processes. The processing of both proprioceptive and visual stimulus information was investigated.Clumsy children were found to process proprioceptive information more slowly than do normal children. However, in this modality, neither the perceptual nor response selection processes were effectively manipulated. By comparison. no difference in the rate of processing of visual information was found. In this modality both processes were effectively manipulated and groups were not differentially affected. Thus, the findings suggest that abnormal clumsiness is associated with an information processing dysfunction which is specific to the proprioceptive modality. Moreover, the findings suggest that clumsiness is not associated with a defect of the response selection process.

The performance of two groups of 20 trained touch typists and one group of 2 0 nontypists was tested on seven different typewriting exercises. Three of these exercises were executed entirely with the right hand and three were completed using only the left. A comparison of performances of the two sides showed, for the typists, no differences between the sides or a difference in favour of the left hand; and for the non-typists, a difference between hands in favour of the right side in two of the three comparisons.A comparison of handwriting performance with the preferred and non-preferred hands was carried out on 80 subjects. Apart from a highly significant difference in performance between the sides in favour of the preferred hand, this task showed, as did the typewriting task, a marked positive correlation between the performance levels of the two sides. These findings are briefly discussed in relation to the training histories of the subjects. INTRODUCTIONIn a recent review of the literature on handedness and motor skill (Provins, 1967),

The present paper examines the control principles underlying rapid manual tracking responses to horizontal double-step stimuli. The paper reports an experiment concerned with responses made to step-stimuli presented in quick succession. The amplitude of the second-step was varied between the initial step-position and the home-base. Double-step response parameters were analysed as a function of the determinant time interval (D) between the second step and the onset of the initial response. The initial response amplitude was observed to vary as a function of D. Amplitude transition functions were constructed representing the transition of the initial response amplitude between the two step positions; their slopes, furthermore, depended on the amplitude of the second target step. No delays in the initial reaction time with the interstimulus interval were observed. Minor delays to the onset of a corrective response were observed. These delays were in part related to a movement time constraint that is independent of any limitations in central processing capacity. The present findings for the manual control system are compared to double-step tracking analyses of the oculomotor control system.