Visual-Propriocetive Correspondence in the Para-Median Plane

2 experiments in which Ss matched a proprioceptively perceived stylus to a visual target in the para-median plane show that Ss make idiosyncratic errors which are stable over periods of at least several days. A technique for comparing visual and proprioceptive spaces is used to Show how matching errors vary within the para-median plane. These errors are interpreted as the result of inadequate inter-calibration of visual and proprioceptive space perception, and their implications for movement control are discussed.     

Control of Trajectory Modifications in Target-Directed Reaching

Human reaching movements to fixed and displaced visual targets were recorded and compared with simulated movements generated by using a two-joint arm model based on the equilibrium-point (EP) hypothesis (λ model) of motor control (Feldman, 1986). The aim was to investigate the form of central control signals underlying these movements. According to this hypothesis, movements result from changes in control variables that shift the equilibrium position (EP) of the arm. At any time, muscle activations and forces will depend on the difference between the arm's EP and its actual position and on the limb's velocity. In this article, we suggest that the direction of EP shift in reaching is specified at the hand level, whereas the rate of EP shift may be specified at the hand or joint level. A common mechanism underlying reaching to fixed and displaced targets is proposed whereby the EP of the hand shifts in a straight line toward the present target. After the target is displaced, the direction of the hand EP shift is modified toward the second target. The results suggest that the rate of shift of the hand EP may be modified for movements in different parts of the work space. The model, with control signals that vary in a simple fashion over time, is able to generate the kinematic patterns observed empirically.     

Reducing Knowledge of Results about Relative versus Absolute Timing: Differential Effects on Learning

The purpose of the present experiment was to examine further earlier suggestions that a reduced relative frequency of knowledge of results (KR) can enhance the learning of generalized motor programs (GMPs) but at the same time degrade parameter learning, compared with giving KR after every trial (Wulf & Schmidt, 1989; Wulf, Schmidt, & Deubel, 1993). In contrast to these earlier studies, here KR was given separately for relative timing and absolute timing. Subjects practiced three movement patterns that required the same relative timing but different absolute movement times. KR was provided on 100% or 50% of the practice trials for relative timing or absolute timing, respectively. In retention and transfer tests, the groups that had had 50% KR about relative timing demonstrated more effective learning of the relative-timing structure, that is, GMP learning, than the groups that had had 100% KR about relative timing. The KR frequency had no effect on parameterization during retention; yet, when transfer to a task with a novel overall duration was required, the groups given 100% KR about absolute timing were more accurate in parameterization than the groups provided with 50% KR about absolute timing. Thus, the reduced relative KR frequency enhanced GMP learning but had no beneficial effect, or even a degrading effect, on parameter learning. The differential effects of a reduced KR frequency on the learning of relative timing and absolute timing also provide additional support for the dissociation of GMP and parameterization processes.     

The Use of Prescanning in the Parameterization of Sequential Pointing and Reaching Movements

The accuracy of reaching movements improves when active gaze can be used to fixate on targets. The advantage of free gaze has been attributed to the use of ocular proprioception or efference signals for online control. The time course of this process, however, is not established, and it is unclear how far in advance gaze can move and still be used to parameterize subsequent movements. In this experiment, the authors considered the advantage of prescanning targets for both pointing and reaching movements. The authors manipulated the visual information and examined the extent to which prescanning of targets could compensate for a reduction in online visual feedback. In comparison with a conventional reaching/pointing condition, the error in pointing was reduced, the eye-hand lead decreased, and both the hand-closure time and the size of the maximum grip aperture in reaching were modulated when prescanning was allowed. These results indicate that briefly prescanning multiple targets just prior to the movement allows the refinement of subsequent hand movements that yields an improvement in accuracy. This study therefore provides additional evidence that the coordinate information arising from efference or ocular-proprioceptive signals can, for a limited period, be buffered and later used to generate a sequence of movements.     

Visual Feedback and Positioning Movements

Subjects (n = 60) performed both the reproduction and learning of a linear positioning movement under one of five visual feedback conditions. Results from two experiments indicated that visual cues from the task display augmented information available from visual feedback of the movement per se. Extraneous cues from the task display have clearly confounded the manipulation of visual feedback in previous positioning studies. When these cues are eliminated, visual distance information seems more useful than visual location information.     

Bilateral Transfer in Tapping Skill in the Absence of Peripheral Information

Bilateral transfer in a fast tapping task was investigated under normal (+FB) and reduced (-FB) feedback conditions, in the -FB experiment 36 Ss were assigned to 3 groups: preferred (PH) to non-preferred (NPH) shift; NPH to PH; and alternating trials of PH and NPH. With + FB 2 further groups of 12 Ss transferred PH to NPH or NPH to PH. 8 preshift and 8 postshift trials were given. The alternating group had 8 PH and 8 NPH trials. In preshift performance increment was found in ail groups except in +FB with NPH. With +FB some facilitation in transfer was obtained for the NPH; under -FB marked positive transfer was found for the PH. Alternating PH and NPH performance conformed to preshift levels. Results were discussed in terms of differential central control processes for the two hands.     

Schema Theory: A Critical Appraisal and Reevaluation

The authors replicated and extended results from the gunfight paradigm (A. Welchman, J. Stanley, M. Schomers, R. Miall, & H. Bulthoff, 2010a) in which participants moved faster when reacting to the perceived initiation of an opponent compared to initiating an action themselves. In addition to replicating these movement time effects, the authors found that time to peak velocity, peak velocity, and movement-endpoint dispersions were similarly impacted. The findings are discussed in terms of a triggering mechanism involved in ballistic and internally generated movements.     

Verbal-Motor Attention-Focusing Instructions Influence Kinematics and Performance on a Golf-Putting Task

The authors examined how varying the content of verbal-motor instructions and requesting an internal versus external focus influenced the kinematics and outcome of a golf putting task. On Day 1, 30 novices performed 120 trials with the instruction to focus attention either on performing a pendulum-like movement (internal) or on the desired ball path (external). After 20 retention trials on Day 2, they performed 20 transfer trials with the opposite instruction. Group differences for retention and a group by block interaction showed that external instruction enhanced movement outcome. Kinematic data indicated that specific instruction content influenced outcomes by eliciting changes in movement execution. Switching from the external to the internal focus instruction resulted in a more pendulum-like movement.     

The Functional Role of Cognitive Frameworks on Visuomotor Adaptation Performance

The authors investigated the effects of cognitive representations of movement directions on sensorimotor adaptation performance. Adaptation performance was measured via a pointing experiment in which participants were provided with visual feedback that was distorted along the midsagittal plane (i.e., left-right reversal). Performance was analyzed relative to participants’ individual adaptation gains and 3 groups were subsequently defined (i.e., skilled, average, and poor adapters). The group separation was kept for the Cognitive Measurement of Represented Directions, which was used to analyze participants’ cognitive representation of movement directions. The results showed that skilled adapters, in contrast to poor adapters, possess a global representation of movement directions aligned to the cardinal axes. The cognitive representation structure hence supports the sensorimotor adaptation performance.     

The Relationship Between Force and Force Variability in Minimal and Near-Maximal Static and Dynamic Contractions

The critical assumption of linearity between force and force variability for rapid movements made by Schmidt, Zelaznik, and Frank (1978) was studied in four experiments in the present study. The first three experiments extended earlier work showing linearity between force and force variability for submaximal force levels in static and dynamic contractions. However, at near-maximal force levels, when force was increased, force variability leveled off and then decreased in both static and dynamic conditions. A fourth experiment using the rapid-timing paradigm showed that increased submaximal loads on the movement produced slight decreases in VE. But when the loads were larger, where force and force variability were no longer linearly related, increased load led to larger decreases in VE. These observations led to the hypothesis that VEt is linearly related to the ratio of force variability to force; data from two experiments are presented that support this idea. The motor-output variability theory seems to hold for a wide range of sub-maximal force values, but needs modification for those conditions where near-maximal forces are required.