Motor preparation of spatially and temporally defined movements: Evidence from startle

This article is available open access through the publisher’s website at the link below. Copyright © 2011 the American Physiological Society.Previous research has shown that the preparation of a spatially targeted movement performed at maximal speed is different from that of a temporally constrained movement (Gottlieb et al. 1989b). In the current study, we directly examined preparation differences in temporally vs. spatially defined movements through the use of a startling stimulus and manipulation of the task goals. Participants performed arm extension movements to one of three spatial targets (20°, 40°, 60°) and an arm extension movement of 20° at three movement speeds (slow, moderate, fast). All movements were performed in a blocked, simple reaction time paradigm, with trials involving a startling stimulus (124 dB) interspersed randomly with control trials. As predicted, spatial movements were modulated by agonist duration and timed movements were modulated by agonist rise time. The startling stimulus triggered all movements at short latencies with a compression of the kinematic and electromyogram (EMG) profile such that they were performed faster than control trials. However, temporally constrained movements showed a differential effect of movement compression on startle trials such that the slowest movement showed the greatest temporal compression. The startling stimulus also decreased the relative timing between EMG bursts more for the 20° movement when it was defined by a temporal rather than spatial goal, which we attributed to the disruption of an internal timekeeper for the timed movements. These results confirm that temporally defined movements were prepared in a different manner from spatially defined movements and provide new information pertaining to these preparation differences

Motor preparation changes with practice

The goal of this dissertation was to examine how the preparation of a movement changes as a result of practice, in order to gain a better understanding of the learning process. To investigate what aspects of a motor action can be prepared in advance, a startle methodology was used as the presentation of a startling stimulus is thought to cause the release of a pre-programmed response. Limits to pre-programming and changes to preparation as a result of learning were examined through practice of movements of varying complexities. Furthermore, movement preparation during physical practice, imagery and observational practice were examined. The use of startle methodology in a learning paradigm allowed for new information regarding the role of motor preparation processes in the learning of novel motor skills. Six experiments are detailed along with their contribution to the advancement of our understanding of what is learned and what is prepared. The first four experiments examined the effects of physical practice on motor preparation and involved movements of varying spatial and temporal characteristics. These experiments provided support that practice results in more accurate pre-programming of motor commands, as well as information pertaining to differences in how spatially targeted and temporally defined movements are prepared. For timing based movements, we found evidence for the reliance on an internal timekeeper, of which the pacemaker pulse is affected by activation level. We also examined the effects of extended physical practice on single component and multiple component movements. In support of previous work, we found multiple element movements had a longer reaction time as compared to single element movements, although this difference was minimized with practice. However, because the startling stimulus triggered all movements at short latencies, we suggested that movement complexity may be more related to the neural commands necessary to produce the movement, rather than a sequencing requirement. The last two experiments examined preparation during motor imagery and observation. Limited support was found during imagery for motor preparation processes that mirror those of intended movements; however observational benefits appeared to be largely perceptual in nature.Education, Faculty ofKinesiology, School ofGraduat

Contextual interference : single-task versus multi-task learning and influence of concurrent temporal interference

Contextual interference (CI) is a learning effect whereby high interference practice conditions produce decreased acquisition performance yet increased retention and transfer performance. Thus, a more difficult practice environment, although initially detrimental to acquisition, actually benefits learning of the skill. Typical CI experimental paradigms involve the comparison of acquisition, retention and transfer performance of multiple tasks under a blocked acquisition schedule (low interference) versus a random acquisition schedule (high interference). Numerous studies have investigated contextual interference and it has been shown to be a stable, robust phenomenon. Two studies involving bimanual coordination were conducted to further examine the contextual interference effect. Experiment 1 involved comparison of acquisition, retention and transfer performance of a single task control group, two task blocked presentation group and a two-task random presentation group. Acquisition data showed both random and control groups outperformed the blocked group in performance of the coordination pattern. This was opposite to the expected CI effect and was attributed to the high number of acquisition trials providing enough time for the learning benefits of the interference to be realized. Retention data did show a typical CI effect for one dependent measure, with the random group significantly outperforming the blocked group. Neither two-task group significantly outperformed the control group, suggesting interference of a second task may be as beneficial to learning as extra practice on the initial task. No group effects were found during transfer performance, however there was a learning effect on the opposite, unpracticed coordination pattern. Experiment 2 examined an alternate form of interference, requiring participants to concurrently verbalize a compatible or incompatible counting pattern while performing a bimanual coordination pattern, to determine if CI effects could be generalized to other forms of interference. No significant group effects were found in acquisition, retention or transfer performance. This was attributed to insufficient interference caused by the counting patterns perhaps due to anchoring strategies of the participants. Analysis of the retention data did provide weak support for a concurrent 2-count pattern providing more interference than a concurrent 4-count pattern. However more research in the area of concurrent temporal interference is required to determine possible interference effects. Scanning data did show a significant improvement in performance of the to-be-learned task as well as the symmetrical bimanual coordination pattern, in support of previous studies. Examination of the sound data provided information regarding anchoring strategies of participants.Education, Faculty ofKinesiology, School ofGraduat

Perturbation Predictability Can Influence the Long-Latency Stretch Response.

Perturbations applied to the upper limbs elicit short (M1: 25-50 ms) and long-latency (M2: 50-100 ms) responses in the stretched muscle. M1 is produced by a spinal reflex loop, and M2 receives contribution from multiple spinal and supra-spinal pathways. While M1 is relatively immutable to voluntary intention, the remarkable feature of M2 is that its size can change based on intention or goal of the participant (e.g., increasing when resisting the perturbation and decreasing when asked to let-go or relax following the perturbation). While many studies have examined modulation of M2 between passive and various active conditions, through the use of constant foreperiods (interval between warning signal and a perturbation), it has also been shown that the magnitude of the M2 response in a passive condition can change based on factors such as habituation and anticipation of perturbation delivery. To prevent anticipation of a perturbation, most studies have used variable foreperiods; however, the range of possible foreperiod duration differs between experiments. The present study examined the influence of different variable foreperiods on modulation of the M2 response. Fifteen participants performed active and passive responses to a perturbation that stretched wrist flexors. Each block of trials had either a short (2.5-3.5 seconds; high predictability) or long (2.5-10.5 seconds; low predictability) variable foreperiod. As expected, no differences were found between any conditions for M1, while M2 was larger in the active rather than passive conditions. Interestingly, within the two passive conditions, the long variable foreperiods resulted in greater activity at the end of the M2 response than the trials with short foreperiods. These results suggest that perturbation predictability, even when using a variable foreperiod, can influence circuitry contributing to the long-latency stretch response

Visual representation of the TMS stimulation points with respect to imperative stimulus onset, represented by downwards pointing arrows.

<p>Visual representation of the TMS stimulation points with respect to imperative stimulus onset, represented by downwards pointing arrows.</p

Mean (+/− SE) motor-evoked potential (MEP) amplitude during the RT interval expressed as a percentage of maximal MEP (Mmax) for 10 ms time bins prior to EMG onset.

<p>The number of trials making up the mean for each of the time points (secondary axis) is represented by columns. The asterisk (*) denotes a significant increase in MEP amplitude as EMG onset approaches.</p

Mean (+/− SE) motor-evoked potential (MEP) amplitude relative to the onset of the imperative stimulus expressed as a percentage of baseline.

<p>Mean (+/− SE) motor-evoked potential (MEP) amplitude relative to the onset of the imperative stimulus expressed as a percentage of baseline.</p