Michael A. Khan

Optimal Control Strategies Under Different Feedback Schedules: Kinematic Evidence

Abstract Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.

Inferring online and offline processing of visual feedback in target-directed movements from kinematic data

Vision plays an important role in the planning and execution of target-directed aiming movements. In this review, we highlight the limitations that exist in detecting visual regulation of limb trajectories from traditional kinematic analyses such as the identification of discontinuities in velocity and acceleration. Alternative kinematic analyses that involve examining variability in limb trajectories to infer visual control processes are evaluated. The basic assumption underlying these methods is that noise exists in the neuromotor system that subsequently leads to variability in motor output. This leads to systematic relations in limb trajectory variability at different stages of the movement that are altered when trajectories are modified during movement execution. Hence, by examining the variability in limb trajectories and correlations of kinematic variables throughout movement for vision and no vision conditions, the contribution of visual feedback in the planning and control of movement can be determined.

The Effect of Practice on the Control of Rapid Aiming Movements: Evidence for an Interdependency Between Programming and Feedback Processing

The purpose of this experiment was to investigate how the control of aiming movements performed as fast and as accurately as possible changes with practice. We examined: (1) the influence of visual feedback on the initial impulse and error correction phases of aiming movements during acquisition; and (2) the effect of removing visual feedback at different levels of practice. Results from the acquisition trials indicated that vision had a major impact on the organization of the initial impulse and error correction phases. Also, consistent with findings from research involving temporally constrained movements, the cost of removing vision was greater after extensive levels than after moderate levels of practice. Collectively, these results denote the importance of visual feedback to the learning of this particular class of aiming movements. Learning appears to be a dual process of improved programming of the initial impulse and increased efficiency of feedback processing. Practice not only acts on programming and feedback processes directly, but also indirectly through a reciprocal interplay between these two processes.

Online versus offline processing of visual feedback in the control of movement amplitude.

Researchers have suggested that visual feedback not only plays a role in the correction of errors during movement execution but that visual feedback from a completed movement is processed offline to improve programming on upcoming trials. In the present study, we examined the potential contribution of online and offline processing of visual feedback by analysing spatial variability at various kinematic landmarks in the limb trajectory (peak acceleration, peak velocity, peak negative acceleration and movement end). Participants performed a single degree of freedom video aiming task with and without vision of the cursor under four criterion movement times (225, 300, 375 and 450 ms). For movement times of 225 and 300 ms, the full vision condition was less variable than the no vision condition. However, the form of the variability profiles did not differ between visual conditions suggesting that the contribution of visual feedback was due to offline processes. In the 375 and 450 ms conditions, there was evidence for both online and offline control as the form of the variability profiles differed significantly between visual conditions.

The Effect of Practice on Component Submovements is Dependent on the Availability of Visual Feedback

Abstract Participants (N = 16) were given extensive practice (1,500 trials) on a perceptual-motor aiming task. The full-vision (FV) group practiced with vision of their response cursor, whereas the no vision (NV) group practiced in a condition without vision. Movements were made as quickly and accurately as possible, and knowledge of results (KR) was provided. The authors tested the importance of vision early and late in practice by transferring participants to the NV condition without KR. The effects of practice differed between the two conditions. The FV group increased the speed of initial impulse to get to the target quickly, then relied on vision so make discrete error corrections. Transfer tests revealed that reliance on vision remained after extensive practice. For the NV group, practice effects were associated with a reduction in the extent to which discrete error corrections were produced.

On the presence and absence of behavioural traits in sport: An example from championship squash match-play

Here we report two experiments that analysed sport (squash) competition as a non-linear system that transits intermittently between different behavioural states. The first experiment involved a perceptual analysis of 60 rallies in which stable behaviour and unstable behaviour, delineated by behavioural transitions (i.e. shot perturbations), were reliably (kappa = 0.930) and validly (kappa = 0.844) identified by independent observers. In addition, experts were better than non-experts at identifying the type of system behaviour (P < 0.01). These results provide for three alternative descriptions: (a) the system is multi-stable and transits between states via the mechanism of instability; (b) the system is bi-stable and abruptly transits between two states, labelled stable and unstable; or (c) the system is mono-stable and displays variability, marked by transient instability, as a result of system perturbations. The second experiment analysed squash behaviour as expressed in the phase relation between the two players from time-motion analysis. The data, from four rallies, yielded evidence of a tight anti-phase coupling with transient phase shifts, or perturbations, that were quickly damped. These data suggest a mono-stable system with a single (anti-phase) attractor onto which system fluctuations are occasionally written. However, these fluctuations failed to correspond with the short perturbations that were identified from perceptual analysis. Together, these results affirm the presence of transient behaviours in squash match-play, although the information that forms these perceptual judgements has yet to be identified.

Online Versus Offline Processing of Visual Feedback in the Production of Component Submovements

Abstract The present authors tested the assumptions in R. S. Woodworths (1899) 2-component model regarding the specific roles of vision in the production of both the initial impulse and the error-correction phases of movement. Participants (N = 40) practiced a rapid aiming task (1,500 trials), with either no visual feedback, vision of only the 1st 50% of the movement, vision of only the 1st 75% of the movement, or vision of the entire movement. Consistent with previous research, the availability of vision over the 1st half of the movement had no effect on aiming accuracy during acquisition. In contrast, when visual feedback was available over the 1st 75% of the movement and the entire movement, initial impulse endpoints were less variable and the efficiency of the error-correction phase was improved. Analysis of spatial variability at various stages in the movement revealed that participants processed visual feedback offline to improve programming of the initial impulse and processed it online in regulating the deceleration of the initial impulse.

Programming strategies for rapid aiming movements under simple and choice reaction time conditions

Increases in reaction time (RT) as a function of response complexity have been shown to differ between simple and choice RT tasks. Of interest in the present study was whether the influence of response complexity on RT depends on the extent to which movements are programmed in advance of movement initiation versus during execution (i.e., online). The task consisted of manual aiming movements to one or two targets (one- vs. two-element responses) under simple and choice RT conditions. The probe RT technique was employed to assess attention demands during RT and movement execution. Simple RT was greater for the two- than for the single-target responses but choice RT was not influenced by the number of elements. In both RT tasks, reaction times to the probe increased as a function of number of elements when the probe occurred during movement execution. The presence of the probe also caused an increase in aiming errors in the simple but not choice RT task. These findings indicated that online programming was occurring in both RT tasks. In the simple RT task, increased executive control mediated the integration between response elements through the utilization of visual feedback to facilitate the implementation of the second element.

Internal and External Focus of Attention in a Novice Form Sport.

Abstract In the current experiment, we examined optimal focus for novices during a movement sequence in which performance was measured on accurate movement form/technique. A novel gymnastics routine was practiced under either an internal skill-relevant, internal skill-irrelevant, external, or no attention focus. Retention and transfer tests were then completed. During acquisition, adopting an internal irrelevant focus significantly improved performance, whereas an external focus degraded performance. There were no significant group differences in the retention and transfer tests. This suggests that learning of movement form/technique did not benefit from a specific focus of attention. The results are interpreted via an attentional capacity viewpoint and the notion that form tasks do not always contain obvious movement effects central to common coding and the constrained action hypothesis.

The use of a distractor-assigned response slows later responding in a location negative priming task

Responding to a target’s location takes longer when that location has recently contained a distractor event (ignored-repetition [IR] trial) relative to when it has been unoccupied (control trial). This is known as thelocation negative priming (NP)effect. We aimed to determine whether the elevated reaction time observed for IR trials was due to the reuse of a distractor location (location locus) and/or to the need to execute a (just inhibited) distractor response (response locus). We isolated these loci latency effects by using many-to-one and one-to-many location-response assignments. Our results showed that reusing a distractor location hastened target processing at that position (facilitative location locus), whereas the production of a distractor response was associated with a time cost (interfering response locus). Accordingly, part of the latency elevation seen with IR trials results from the need on these occasions to execute a just inhibited (distractor) response, and, hence, the location NP effect has a response locus.