Moving the Arm at Different Rates: Slow Movements are Avoided

Qualitative and quantitative changes characterize locomotion and rhythmic interlimb coordination at different speeds. Legs and hands do not move more or less quickly; they also adopt different relative coordination patterns. In the present article, the authors asked whether similar transitions occur for unimanual hand movements when speed is slowed below the preferred speed. Participants moved a handheld dowel back and forth between 2 large circular targets in time with a metronome at periods between 370 ms and 1667 ms. The authors analyzed the kinematics of participants’ movements at each period and found that proportional dwell time and number of peaks in the velocity profile increased as driving periods increased. Path lengths and peak velocities remained relatively constant for driving periods exceeding 800 ms. Participants made only gradual changes to their movement parameters, so that they went from a continuous mode to a more discrete mode of behavior for longer driving periods. Thus, unlike for rhythmic bimanual movements or locomotory patterns, there are quantitative but no clear qualitative changes for unimanual movements. The results suggest that participants tried to move close to their preferred tempo at different rates, and that they avoided moving slowly.     

Determining the Temporal Limits of a Visual Sample for Visual Regulation

The author examined the minimum amount of time needed for vision to increase aiming accuracy and decrease movement duration. Participants selected when they would receive a visual sample during aiming movements by pressing a switch held with the left hand. The sample was one of the following durations: 40 ms, 30 ms, 20 ms, 10 ms, or 0 ms (no vision). Decreased accuracy in the no-vision condition compared to the vision conditions was observed when the duration of the impending sample was unknown (Experiment 1). Samples 40 ms in duration were sufficient to decrease endpoint variability when the duration of the sample was known before the movement (Experiment 2). These results indicate that short visual samples can be used to decrease movement time and increase accuracy and that knowledge of the impending visual context can impact the individual's subsequent behavior.     

The Visuomotor Mental Rotation Task: Visuomotor Transformation Times Are Reduced for Small and Perceptually Familiar Angles

In the visuomotor mental rotation (VMR) task, participants point to a location that deviates from a visual cue by a predetermined angle. This task elicits longer reaction times (RT) relative to tasks wherein the visual cue is spatially compatible with the movement goal. The authors previously reported that visuomotor transformations are faster and more efficient when VMR responses elicit a degree of dimensional overlap (i.e., 0° and 5°) or when the transformation involves a perceptually familiar angle (i.e., 90° or 180°; K. A. Neely & M. Heath, 2010b). One caveat to this finding is that standard and VMR responses were completed in separate blocks of trials. Thus, between-task differences not only reflect the temporal demands of the visuomotor transformations, but also reflect the temporal cost of response inhibition. The goal of this study was to isolate the time cost of visuomotor transformations in the VMR task. The results demonstrated that visuomotor transformations are more efficient and effective when the response entails a degree of dimensional overlap between target and response (i.e., when the angular disparity between the responses is small) or when the transformation angle is perceptually familiar.     

Coupling of Eye,Finger, Elbow,and Shoulder Movements During Manual Aiming

Temporal and spatial coupling of point of gaze (PG) and movements of the finger, elbow, and shoulder during a speeded aiming task were examined. Ten participants completed 40-cm aiming movements with the right arm, in a situation that allowed free movement of the eyes, head, arm, and trunk. On the majority of trials, a large initial saccade undershot the target slightly, and 1 or more smaller corrective saccades brought the eyes to the target position. The finger, elbow, and shoulder exhibited a similar pattern of undershooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at the target well in advance of the finger. There was a clear temporal coupling between primary saccade completion and peak acceleration of the finger, elbow, and shoulder. The initiation of limb-segment movement usually occurred in a proximal-to-distal pattern. Increased variability in elbow and shoulder position as the movement progressed may have served to reduce variability in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the position of the finger and the target late in the movement.     

The Role of Oculomotor Information in the Learning of Sequential Aiming Movements

With their eyes initially on either the home, midline, or final end position, 30 participants practiced a 2-target aiming movement. After 120 acquisition trials, participants performed a retention test and were then transferred to each of the other 2 eye conditions. During acquisition, all groups improved over practice, but the home group showed the greatest improvement. The temporal improvement was most pronounced in the times spent after peak velocity. Retention and transfer tests indicated that participants performed best under eye-movement conditions that were the same as the 1 they had practiced in. There was also positive transfer of training between conditions in which the oculomotor information was similar. Thus, to optimize learning, one should practice under the same afferent and oculomotor conditions that will be required for the final performance.     

Decay in Visuomotor Representations During Manual Aiming

The time course of the decay of spatial representations used for planning and controlling manual aiming has not been established. The authors' purpose in the present investigation was to generate a psychometric function for memory-guided reaching movements. Eight university-aged students performed a reciprocal tapping task for 10 s. Participants could see the targets for 5 s; then, vision of the targets was occluded. The present findings provide mixed support for 2 prominent theories concerning memory representations. Variability increased concurrently with the removal of vision of the targets, supporting the real-time hypothesis. However, a brief plateau in the curve was apparent for approximately 2 s after vision was removed, consistent with the use of a highly accurate representation for action.     

Actions modulate attentional capture

The purpose of the present study was to determine whether the action system plays a role in determining which stimulus characteristics capture attention by assessing the interference effects caused by dynamic discontinuities that have similar attention-capturing properties, but different action affordances. Results revealed that offset distractors caused significant interference when onset targets were presented in a keypress task, but did not increase reaction times when the same onset targets were presented in a goal-directed aiming task. In contrast, onset distractors caused interference when offset targets were presented in both keypress and aiming tasks. This pattern of results suggests that the attentional set, and thus the properties of stimuli that capture attention, is modulated by the interaction between stimulus and response expectations.     

Specificity of Learning in a Video-Aiming Task: Modifying the Salience of Dynamic Visual Cues

The authors investigated whether the salience of dynamic visual information in a video-aiming task mediates the specificity of practice. Thirty participants practiced video-aiming movements in a full-vision, a weak-vision, or a target-only condition before being transferred to the target-only condition without knowledge of results. The full- and weak-vision conditions resulted in less endpoint bias and variability in acquisition than did the target-only condition. Going from acquisition to transfer resulted in a large increase in endpoint variability for the full-vision group but not for the weak-vision or target-only groups. Kinematic analysis revealed that weak dynamic visual cues do not mask the processing of other sources of afferent information; unlike strong visual cues, weak visual cues help individuals calibrate less salient sources of afferent information, such as proprioception.     

The effect of a non-steroidal anti-inflammatory drug on two important predictors for accidental falls: Postural balance and manual reaction time. A randomized, controlled pilot study

Accidental falls in older individuals are a major health and research topic. Increased reaction time and impaired postural balance have been determined as reliable predictors for those at risk of falling and are important functions of the central nervous system (CNS). An essential risk factor for falls is medication exposure. Amongst the medications related to accidental falls are the non-steroidal anti-inflammatory drugs (NSAIDs). About 1-10% of all users experience CNS side effects. These side effects, such as dizziness, headaches, drowsiness, mood alteration, and confusion, seem to be more common during treatment with indomethacin. Hence, it is possible that maintenance of (static) postural balance and swift reactions to stimuli are affected by exposure to NSAIDs, indomethacin in particular, consequently putting older individuals at a greater risk for accidental falls. The present study investigated the effect of a high indomethacin dose in healthy middle-aged individuals on two important predictors of falls: postural balance and reaction time. Twenty-two healthy middle-aged individuals (59.5 ± 4.7 years) participated in this double-blind, placebo-controlled, randomized crossover trial. Three measurements were conducted with a week interval each. A measurement consisted of postural balance as a single task and while concurrently performing a secondary cognitive task and reaction time tasks. For the first measurement indomethacin 75 mg (slow-release) or a visually identical placebo was randomly assigned. In total, five capsules were taken orally in the 2.5 days preceding assessment. The second measurement was without intervention, for the final one the first placebo group got indomethacin and vice versa. Repeated measures GLM revealed no significant differences between indomethacin, placebo, and baseline in any of the balance tasks. No differences in postural balance were found between the single and dual task conditions, or on the performance of the dual task itself. Similarly, no differences were found on the manual reaction time tasks. The present study showed that a high indomethacin dose does not negatively affect postural balance and manual reaction time in this healthy middle-aged population. Although the relatively small and young sample limits the direct ability to generalize the results to a population at risk of falling, the results indicate that indomethacin alone is not likely to increase fall risk, as far as this risk is related to abovementioned important functions of the CNS, and not affected by comorbidities.     

The utilization of visual information in the control of reciprocal aiming movements

Two experiments examined on-line processing during the execution of reciprocal aiming movements. In Experiment 1, participants used a stylus to make movements between two targets of equal size. Three vision conditions were used: full vision, vision during flight and vision only on contact with the target. Participants had significantly longer movement times and spent more time in contact with the targets when vision was available only on contact with the target. Additionally, the proportion of time to peak velocity revealed that movement trajectories became more symmetric when vision was not available during flight. The data indicate that participants used vision not only to 'home-in' on the current target, but also to prepare subsequent movements. In Experiment 2, liquid crystal goggles provided a single visual sample every 40 ms of a 500 ms duty cycle. Of interest was how participants timed their reciprocal aiming to take advantage of these brief visual samples. Although across participants no particular portion of the movement trajectory was favored, individual performers did time their movements consistently with the onset and offset of vision. Once again, performance and kinematic data indicated that movement segments were not independent of each other.