Cinematographical Analysis of Movement Pathway Constraints in Rapid Target-Striking Tasks

Predictable real-time constraints reveal anticipatory strategies of coupled planning in a sequential pick and place task

Planning a sequence of two motor elements is much more than concatenating two independent movements. However, very little is known about the cognitive strategies that are used to perform fluent sequences for intentional object manipulation. In this series of studies, the participants’ task was to reach for and pick to place a wooden cylinder to set it on a place pad of three different diameters, which served to modify terminal accuracy constraints. Participants were required to perform the sequences (1) at their preferred speed or (2) as fast as possible. Action kinematics were recorded with the Qualisys motion-capture system in order to implement a real-time protocol to get participants to engage in a true interactive relation. Results revealed that with low internal constraints (at preferred speed), low coupling between the two elements of the motor sequence was observed, suggesting a step-by-step planning strategy. Under high constraints (at fastest speed), an important terminal accuracy effect back propagated to modify early kinematic parameters of the first element, suggesting strong coupling of the parameters in an encapsulated planning strategy. In Studies 2 and 3, we further manipulated instructions and timing constraints to confirm the importance of time and predictability of external information for coupled planning. These findings overall sustain the hypothesis that coupled planning can take place in a pick and place task when anticipatory strategies are possible. This mode of action planning may be the key reason why motor intention can be read through the observation of micro variations in body kinematics.

Effects of auditory feedback on movements with two-segment sequence and eye-hand coordination

The present study investigated the effect of auditory feedback on planning and control of two-segment reaching movements and eye-hand coordination. In particular, it was examined whether additional auditory information indicating the progression of the initial reach (i.e., passing the midway and contacting the target) affects the performance of that reach and gaze shift to the second target at the transition between two segments. Young adults performed a rapid two-segment reaching task, in which both the first and second segments had two target sizes. One out of three auditory feedback conditions included the reach-progression information: a continuous tone was delivered at a consistent timing during the initial reach from the midway to the target contact. Conversely, the other two were control conditions: a continuous tone was delivered at a random timing in one condition or not delivered in the other. The results showed that the initial reach became more accurate with the auditory reach-progression cue compared to without any auditory cue. When that cue was available, movement time of the initial reach was decreased, which was accompanied by an increased peak velocity and a decreased time to peak velocity. These findings suggest that the auditory reach-progression feedback enhanced the preplanned control of the initial reach. Deceleration time of that reach was also decreased with auditory feedback, but it was observed regardless of whether the sound contained the reach-progression information. At the transition between the two segments, the onset latencies of both the gaze shift and reach to the second target became shorter with the auditory reach-progression cue, the effect of which was pronounced when the initial reach had a higher terminal accuracy constraint. This suggests that the reach-progression cue enhanced verification of the termination of initial reach, thereby facilitating the initiation of eye and hand movements to the second target. Taken together, the additional auditory information of reach-progression enhances the planning and control of multi-segment reaches and eye-hand coordination at the segment transition.

Test of Validity of Fitts' Index of Difficulty as a Measure of Task Difficulty

This study investigated the validity of Fitts' index of difficulty as a measure of task difficulty perceived by the performer. Eight subjects performed self-terminated horizontal elbow-extension movements toward targets of three indices of difficulty in two task conditions. In the target-size condition, triceps and biceps activities during acceleration and deceleration respectively decreased with increasing index of difficulty, resulting in a lower peak velocity and longer movement time. In the movement amplitude condition, however, triceps activity after movement onset and biceps activity during deceleration increased with increasing index of difficulty, resulting in a higher peak velocity. The movement time also increased as a function of the index of difficulty given increase in the distance traveled by the limb. These results suggest that Fitts' index of difficulty may not reflect the difficulty of task performance because its effect on the pattern of motor output is dependent upon the task variable manipulated in measuring the index of difficulty.

Memory drum theory's C movement: revelations from Franklin Henry

Franklin Henry's "memory drum" theory of neuromotor reaction (Henry & Rogers, 1960) was one of the most influential studies of the response programming stage of information processing. The paper is the most-cited study ever published in the Research Quarterly for Exercise and Sport. However, few people know there is a noteworthy error in the paper, namely in the description of the C movement, the most complicated of the three responses studied. Henry himself was unaware of the error for nearly 20 years after the paper's publication. The purpose of our paper is to accord the factual record its due respect by revealing the history about the error and its correction. The data are in the form of the original 1960 paper which describes the C movement, a paper by Howell (1953), and personal letters from Henry dating from 1979, when the error was first discovered, and continuing through 1986. In one letter, Henry attributed the error to a mild and specific form of aphasia, manifested by word reversals, from which he suffered throughout his scholarly life. Such a revelation makes the career of this remarkable scholar even more remarkable.

Planning and control of sequential rapid aiming in adults with Parkinson's disease

Eight people with Parkinson's disease (PD), 8 age-matched older adults, and 8 young adults executed 3-dimensional rapid aiming movements to 1, 3, 5, and 7 targets. Reaction time, flight time, and time after peak velocity to the 1st target indicated that both neurologically healthy groups implemented a plan on the basis of anticipation of upcoming targets, whereas the PD group did not. One suggested reason for the PD group's deficiency in anticipatory control is the greater variability in their initial force impulse. Although the PD group scaled peak velocity and time to peak velocity similarly to the other groups, their coefficients of variation were greater, making consistent prediction of the movement outcome difficult and thus making it less advantageous to plan too far in advance. A 2nd finding was that the PD group exhibited increased slowing in time after peak velocity in the final segments of the longest sequence, whereas the other 2 groups did not. The increased slowing could be the result of a different movement strategy, increased difficulty modulating the agonist and antagonist muscle groups later in the sequence, or both. The authors conclude that people with PD use more segmented planning and control strategies than do neurologically healthy older and young adults when executing movement sequences and that the locus of increased bradykinesia in longer sequences is in the deceleration phase of movement.

Spatial Accuracy Demand in Aiming Movements: Kinematic Analysis of Subtended Angle and Tolerance Width

Subtended angle has been assumed to be an important factor in both response programming time and kinematic characteristics of aiming movements. Support for this assumption has come mainly from studies in which circular targets have been used. However, with circular targets, the subtended angle covaries with the size of the target in the principal direction of the movement (tolerance width). The purpose of this study was to examine the effects of tolerance width and subtended angle on aiming movement with multiple targets. Participants first hit a 5-cm-diameter circular target located 8 cm to the left of a starting position and then moved another 8 cm left to hit either a 5-cm diameter circular target or a 5- × 1-cm rectangular target oriented either horizontally or vertically, depending on the condition. Analysis showed that reaction times and movement times were longer for the vertical rectangular target, which had a smaller tolerance width than the other two targets. In addition, the vertical rectangular target also showed a greater percentage of secondary-submovement trials, lower movement velocity, and higher peak vertical displacement. Overall, the results indicate that the tolerance width of the target may impose more constraints on aiming movements than subtended angle.

Planning short pointing sequences

An experiment tested the hypothesis that fast, short sequences of movements are planned as a whole, before movement inception. The experimental task consisted of pointing to either one (one-step condition), or two (two-step condition) visual targets aligned along the mid-sagittal axis in a horizontal plane. There were nine possible arrangements of the targets resulting from all combinations of three distances (5, 10, 15 cm), and two trial orders (blocked or random). Performances were characterised by reaction time (RT), movement kinematics, and spatial accuracy. Compared with one-step trials, the first movements of two-step trials had longer RTs (length effect), particularly in random sessions, and when the sequences included short-distance targets. There were also differences in duration (one-target advantage), velocity profile and spatial accuracy that did not depend on the characteristics of the second movement. The results are inconsistent with the assumption that two-step sequences are planned as a whole. Instead, they are in keeping with the alternative hypothesis that part of the preparation of the second step takes place during the execution of the first step.

Effect of task difficulty on muscle activation patterns during rapid single-joint movements

This study investigated the effect of spatial accuracy demands on movement organization by analyzing the amplitude of the agonist and antagonist muscle activities emerging during horizontal elbow-flexion movements toward spatial targets of varying difficulties. 8 subjects performed elbow-flexion movements toward targets of 3 sizes, located at 2 distances, as rapidly and accurately as possible. For each movement, the elbow angles and the activities of biceps brachii, brachioradialis, and lateral and long heads of triceps brachii were measured. Analysis on the kinematic variables indicated that final elbow angle and peak velocity decreased with increasing index of difficulty of the task in both movement-amplitude conditions. However, movement time increased with increasing index of difficulty. The amplitude of agonist and antagonist muscle activities measured for 100 msec. before movement initiation was also shown to decrease with increasing index of difficulty. Agonist and antagonist muscle activities measured during acceleration phase displayed similar patterns with those of premovement. These results suggest that the task difficulty affects movement organization, and the control system decreases the amplitude of agonist and antagonist muscle activities with an increase in the index of difficulty to enhance the controllability of the limb.

Peripheral constraint versus on-line programming in rapid aimed sequential movements

The purpose of this investigation was to examine how the programming and control of a rapid aiming sequence shifts with increased complexity. One objective was to determine if a preprogramming/peripheral constraint explanation is adequate to characterize control of an increasingly complex rapid aiming sequence, and if not, at what point on-line programming better accounts for the data. A second objective was to examine when on-line programming occurs. Three experiments were conducted in which complexity was manipulated by increasing the number of targets from 1 to 11. Initiation- and execution-timing patterns, probe reaction time (RT), and movement kinematics were measured. Results supported the peripheral constraint/pre-programming explanation for sequences up to 7 targets if they were executed in a blocked fashion. For sequences executed in a random fashion (one length followed by a different length), preprogramming did not increase with complexity, and on-line programming occurred without time cost. Across all sequences there was evidence that the later targets created a peripheral constraint on movements to previous targets. We suggest that programming is influenced by two factors: the overall spatial trajectory, which is consistent with Sidaway's subtended angle (SA) hypothesis (1991), and average velocity, with the latter established based on the number of targets in the sequence. As the number of targets increases, average velocity decreases, which controls variability of error in the extent of each movement segment. Overall the data support a continuous model of processing, one in which programming and execution co-occur, and can do so without time cost.

Distributed Control in Rapid Sequential Aiming Responses

The preparation and on-line control of short, rapid sequential aiming responses were studied in 3 experiments. Participants (N = 12 in Experiments 1 and 2, and 20 in Experiment 3) produced 3-segment responses (a) within self-initiation, simple reaction time (RT), and choice RT paradigms (Experiment 1); (b) without visual feedback under self-initiation conditions (Experiment 2); and (c) with and without visual feedback under simple RT conditions (Experiment 3). In all conditions in which participants initiated movement in response to an external imperative signal, the 2nd response segment was performed consistently slower than preceding and succeeding response segments. That pattern of segmental movement times was found whether or not visual feedback was available but was not evident when participants self-initiated their responses with or without visual feedback. The findings rule out the possibility that subjects' use of visual feedback is responsible for the slowing of the 2nd response segment under RT conditions and suggest that the programming of rapid sequential aiming responses can be distributed in pre- and postinitiation intervals.

Precision hypothesis and the end-state comfort effect

Recently, motor control research has emphasized the planning of macroscopic aspects of control. In object manipulation studies, when participants complete a movement in a comfortable posture, an end-state comfort effect is attained. One explanation for this effect is the precision hypothesis, which states that precision increases when participants are in a comfortable position. This research directly tests the precision hypothesis in two experiments. In Experiment 1, participants picked up a dowel and touched a large or small target on a wall. For the second experiment, the same procedure was followed using a pinpoint target. The probability analyses of the first experiment indicated that the end-state comfort effect was magnified in the small target condition and that the point-of-change effect (Short and Cauraugh, 1997) appeared only when end-state comfort was magnified. Error analyses in Experiment 2 showed that participants were more accurate when in a more comfortable position. The present findings indicate that the precision hypothesis plays a significant role in the end-state comfort effect.

Planning macroscopic aspects of manual control: end-state comfort and point-of-change effects

A recent emphasis in motor control research is the planning of macroscopic features and how variables such as efficiency and comfort influence the planning process. This paper extends the work by Rosenbaum and Jorgensen (1992) by further studying the end-state comfort effect. In the first experiment, participants picked up a dowel using an underhand or overhand grip and touched one end to a numbered target on the wall. The height of the #9 target was set at the height of participants' right shoulder. The second experiment involved awkwardness ratings. Participants touched the 14 targets with the dowel as well as with a small dumbbell and the comfort of the end position was rated on a seven-point scale. In the third experiment, participants moved a dumbbell to the targets in the same procedure as the first experiment. Overall, the probability analyses indicated that as the end-state comfort effect was magnified, the sequential effect vanished and a distinct point-of-change effect appeared. Optimization theory and the knowledge model readily explained the phenomena of the end-state comfort effect, the sequential effect, and the point-of-change effect. The present findings indicate that comfort has a powerful influence on the planning of motor performance.