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Studies investigating human information processing have provided evidence that in some cases, movements can be prepared in advance. Although evidence for motor preparation has been shown at cortical and spinal levels, motor preparation at a subcortical level is not well described. One line of inquiry has involved the use of a startling acoustic stimulus (115-124 dB) that can act as an early trigger for pre-programmed actions in reaction time (RT) tasks. In light of this new research paradigm, the startle reflex may be used as a tool to investigate motor preparation. Here, six experiments were conducted that work towards the goals of understanding the mechanism of RT shortening due to startle, and motor preparation at a subcortical level. The first section (2 experiments) of this dissertation provides evidence that when a motor action can be prepared in advance, it is pre-programmed and stored subcortically awaiting the normal cortical “go” signal. A startle appears to activate structures directly that are involved with the voluntary response channel leading to early triggering of the pre-programmed response, and dramatically reduced RT. In the current dissertation we investigated alternative mechanisms to explain startle RT facilitation, including the stimulus intensity effect, and a fast transcortical route, with results supporting the original subcortical storage hypothesis. The second section (4 experiments) presents data which together provide insight into motor programming processes, and the circumstances under which a response is pre-programmed. For example, when the possibility of not having to make the response existed, a known response was not pre-programmed. Similarly, no pre-programming occurred when certainty existed regarding when to respond. However, while a previous experiment showed that having to make a choice between several response alternatives precluded pre-programming, this dissertation shows that if possible response alternatives are not in conflict with one another, multiple responses can be prepared in parallel. Finally, the complexity of a response such as one involving multiple sequenced sub-components may limit the ability to pre-program in a simple RT task. Taken together, these results suggest that pre-programming is dependent on the task characteristics and appears to involve implementation of strategies to increase programming efficiency. / Education, Faculty of / Kinesiology, School of / Graduate

<p>A fundamental decision when interacting with objects in our environment involves hand selection. Two major factors that influence this choice include handedness (the proficiency of one hand over the other) and the spatial relationships perceived between the object and both effectors (Gabbard & Rabb, 2000). Previous studies have altered the location of an object in space and the complexity of a task as it relates to hand choice decisions (Bryden et al., 2003; Gabbard et al., 2003; Mamalo et al., 2006). This thesis investigates the idea of reaching toward a series of predictable target locations and its effect on the frequency of hand use when compared to unpredictable reaches. Predictable reaches allow participants to assign hand use prior to movement initiation. Participants reached to a series of 3-target sequences in one of two groups: unpredictable reaches, selecting a hand to reach each target as it appeared; and predictable reaches, where the target sequence was presented prior to initiating a reach. Unpredictable reaches at different hand positions in space demonstrate that object proximity often mediates hand choice by promoting use of the effector that affords the shortest reaching amplitude. Further, predictive reaches demonstrate a preference to complete larger reaching amplitudes earlier in the sequence in order to place both hands in a position where object proximity mediates hand choice later in the sequence. Overall, predictable reaches seem to resemble the end-state comfort effect (Rosenbaum, 1992), where participants change their approach to executing reaches when they know the sequence of targets that follows.</p> / Master of Science in Kinesiology

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Studies of speech production and its control have traditionally focused on acoustic parameters and/or articulatory configurations of the end result of the production process as the target of speech production. The representations of production target, however, are far richer than the stereotypical acoustic/articulatory features that have been identified from those traditional studies. Speech production is a process through which mental representations of a language are transformed into vocal tract movements and sounds as physical entities. Thus, the speech production target includes these complete representations, and in order to fully understand how the target is controlled, we need to perturb the production process. This paradigm allows us to see how the production system as a whole corrects behavior in response to the perturbation. By systematically introducing perturbation, it is possible to examine what is needed for the system to detect an error, and how such an error is reduced. This, in turn, enables us to have a better understanding of what the speech production target is and how it is defined. A series of experiments were carried out to examine this issue in this thesis, using a real-time auditory perturbation paradigm. This paradigm perturbs the auditory feedback speakers receive while they are producing a speech segment. In response to the perturbation, subjects spontaneously change their articulation to compensate. The results showed that 1) the speech production target is not a list of independently controlled acoustic features but is a multi-dimensionally defined category that is language dependent 2) spectral and temporal aspects of speech motor control show the same results 3) similar compensation behavior is observed even with using an unfamiliar tool to produce a vowel-like sounds, and 4) an intention to produce a speech category may be manifested in ways that are different than behavior in other motor control studies such as reaching. / Thesis (Ph.D, Psychology) -- Queen's University, 2013-09-30 22:44:48.165

Human soleus H-reflex gain was measured in supine lying and in standing vertically while stabilised by a backboard. H-reflex amplitude was less in stabilised standing than in supine lying. The reduction was partly due to the effect of gravitational load. When the same load was applied (by compression of the body between shoulders and feet) while lying supine the corresponding reduction was 70%. The results are discussed in relation to possible gravitational load receptors. In a second series of experiments a collapsible landing platform was used to differentiate between reflex and programmed contributions to EMG activity in landing from a jump. Post-landing activity of the calf muscles was a short latency spinal reflex triggered by ankle rotation. In the rectus femoris muscle, activity was programmed for short falls and had a reflex component in longer falls. When the collapsible platform caused a landing to occur at a time later than anticipated, reflex gain was increased in the gastrocnemius, biceps femoris and rectus femoris muscles. Experimental results were consistent with the time that would be required for descending pathways to modulate the reflex gain and an appropriate model is proposed.