The effect of temporal and force changes on the patterning of sequential movements.

This article examines the programming of relatively long sequences of action with the control of sequential movements being effected through the use of a tapping task involving a sequence of five taps. Subjects were required to tap with their right hand at rates of 150, 200, and 250 ms. There were two conditions, with subjects being required either to increase, in condition 1, or to decrease, in condition 2, the force at one of the five tap positions (all five tap positions were examined), then return to the previous force level. Changes in timing resulting from variations in the force characteristics have previously been discussed in terms of changes in the organizational time required (Semjen, Garcia-Colera, & Requin, 1984). The current study breaks the intertap interval down into two separate components: the contact interval (finger in contact with the key) and the non-contact interval (interval preceding the tap). Although changes in the non-contact interval could be explained in terms of changes in the organizational time required, changes in the contact interval appeared to be a result of the mechanical changes in force.

Visually based amendments of aiming movements: a reappraisal of Christina (1970).

The present paper examines the processing of visual information during the initial and corrective phases of an aimed movement. Visual processing in the corrective phase is related to the nature of the error in the initial phase. By producing a deliberate error, the system knows the approximate amplitude and direction in advance, allowing for the preprogramming of the corrective response. The final response, however, awaits visual confirmation with a processing time on the order of 130 msec. This strategy is feasible only if the variability in the initial response is constrained, which is the role of an additional very rapid feedback loop (70 to 100 msec.).

Do children with a specific reading disability have a general serial-ordering deficit?

Two experiments are described in which reading disabled subjects and their normal controls were tested for their ability to abstract sequential regularities from a noisy background. Subjects were presented with an adaptation of the repeated digits task of Hebb (1961) and its spatial analogue the Corsi Blocks (Milner, B. Br. Med. Bull. 27, 272-277, 1971). Normal subjects had a digit span significantly better than their block span and also significantly better than that of the disabled readers. This suggested that normal subjects have better defined "storage filters" for digits or a specific advantage in the construction of 'transitory filters' for verbal material. There were no differences between groups on block span. On the repeated digit sequences normal readers abstracted a relatively stable "storage filter" in the first five recurrent trials whereas the disabled readers showed no discrimination until the last five recurrent trials. On the repeated blocks task the disabled group performed as well as normal readers. Taken together this date gives strong evidence for a specific deficit in verbal serial organization in disabled readers but does not support a general deficit in serial organization.

Alcohol and human performance.

The present paper presents a comprehensive review of studies concerned with the effects of alcohol on human performance. It attempts to review the studies within the framework of the information processing model. The effects of alcohol on information processing and transmission rates, sensory and perceptual processes, motorcontrol processes, attentional processes, and cognitive processes are described and discussed. It is proposed that such a processes analysis of human performance is a useful vehicle to describe the specific effects of alcohol. From the review it is concluded that much of the evidence from simple task description is equivocal. However, when information load is increased, when the stimulus-response incompatibility increases, and when the number of competing information processes occur in 'parallel', then a strong, consistent and coherent pattern of performance deterioration is associated with alcohol consumption.

Response amendments during manual aiming movements to double-step targets.

The present paper reports a double-step analysis of a discrete aiming movement. A second target step was presented during the trajectory of the response to an initial step and represented an artificially induced movement error signal. Two stimulus patterns involving steps in the same direction (an undershoot error signal) and opposite direction (an overshoot error signal) to the initial step were examined. Moreover, in a random error condition the subject had no advance information regarding the direction of the error. In a deliberate error condition the subject knew in advance whether any subsequent error would be an undershoot or overshoot. Response parameters were considered as a function of the interstep interval which was randomly varied across trials. In terms of movement time, the standard deviations and a constant amendments score of double-step trials, subjects could respond more appropriately and effectively to a deliberate rather than a random error, and an undershoot error rather than an overshoot error. These results are discussed in terms of a mixed-mode of visuo-spatial error updating and related to the generalized motor program hypothesis.

The relationship of target and response complexity in coincident timing performance.

This paper reports two experiments concerned with the interaction of response and target factors in a coincident timing situation. Coincident timing involves executing a response to intercept a moving target. The target response relationship was manipulated in the first experiment by providing some targets with no structure (linear path) and others containing 1 and 2 bounce points. In the second experiment, responses required 0, 1, or 2 reversals in direction. The results provide tentative support for the notion that structure in the target path could be linked to the key temporal response dynamics for improved performance consistency, and that subjects may alter their response structure to incorporate this linkage. This can be further extended to the advantage of simply moving while perceiving movement. This paper stresses the importance of examining the perceptual and motor requirements of the coincident timing skill in unison.

The planning of precision movements.

Two experiments are reported in which subjects were required to make rapid aiming movements to targets of various sizes. Probe reaction time (RT) procedures were used to investigate the preparation of the response to the target. It was proposed that if the precision of movement was planned in advance, this would be reflected by the lengthening of RTs to probes presented during the latency phase of the response. The more precise the movement (to smaller targets) the longer will be the delays to the probes. The results generally supported the prediction and the probe RTs were correlated with target size. There was also some evidence that the probe was lengthening during the movement and in the region of the target.

The latency of aiming movements.

The latency of movements requiring successively more and more precision was investigated in three simple reaction time experiments. The movements involved a horizontal arm sweep aimed at small circular targets. The results failed to provide strong support for the hypothesis that movements, and hence motor programs, requiring greater precision had longer latencies. The results are discussed in terms of a neural organization hypothesis, relating change in response complexity to the spatial and temporal structure of the motor program.

The use of ischemic nerve block procedures in the investigation of the sensory control of movements.

In this study the ischemic nerve block (INB) technique is investigated as a procedure for blocking afferent information in the study of the sensory control of movements. A movement replication task is used. The results suggest that the elbow, wrist and metacarpal-phalangeal joints are at three different stages of sensory information loss or reduction. With the index finger, replications of joint position are not made in the correct direction significantly greater than chance. Error is also largest for the finger. The elbow joint appears to be least affected by the block. Motor impairment under the block is also investigated and the results show that there is a marked decrement in the force exerted in flexion and extension of the index finger, wrist and elbow joints after sensory drop-out. This finding indicates that there is substantial motor impairment of movements distal to the block. The limitations of the INB technique as a procedure for investigating the control of movement under conditions of sensory loss are discussed.

Response complexity and the latency of different movement patterns.

Two series of experiments are described in which RT of responses of varying complexity is investigated. Complexity of arm movements was manipulated in terms of (a) the amount of force exerted in resisted movements, (b) the distance moved by the limb and the direction of movement, using reversing or continuing movements, and (c) the combining of the arms in reversing and continuing movements. Simple and two-choice RT situations were used. As response complexity increased in terms of the number of sets of response units that have to be organized into a spatio-temporal sequence, the latency correspondingly increased. However latency was not affected by changes in the amount of force exerted, or in simple reversal movements. The implications of these results are discussed.

The effects of changes in direction, load, and amplitude of movement on gradation of effort.

Gradation of a response is a form of amplification control which determines that the response as a whole is appropriately graded in effort. The present study is an investigation of the effects of changes in resistance to cranking, amplitude of movement, and direction of movement on the gradation of the response in hand cranking. Criteria of gradation were derived from strain gauge and EMG records. A modification in gradation occurred principally when the resistance to movement changed appreciably. The findings are discussed in terms of one basic pattern of organization that is used, despite variations in task conditions.

Latency and response complexity.

Two experiments were conducted in which the latency of movement responses of varying complexity was investigated. The complexity of an arm sweep movement was varied by (a) increasing the extent of movement from 6 in. to 18 in., (b) reversing the movement, and (c) by making two or three pauses in an on-going movement. The results only partially supported the hypothesis that the latency of a response is related to the complexity of the movement pattern. Specifically RT was longer when the response involved significant changes in the temporal organization of the movement pattern.

Effector organization and "gradation" of effort.

It is proposed that an aspect of the effector organization process is the gradation of the response. Gradation was investigated in a hand cranking task by using strain-gauge and electromyographic recording techniques. Criteria of gradation were related to (a) the impulsive force at a particular point in the cycle of movement, (b) an index of the work done per unit of time, (c) the degree of muscle activity in each of the 6 muscles analyzed, and (d) an index of muscle activity based on the pen deflection of an EMG record. Further, two criteria of the organization of the force were employed - the force range and the consistency of the force range. None of the criteria of gradation was closely related to speed of performance, but the organizational criteria showed a trend toward being related to speed. The implications of these findings are discussed.