Coordinated gaze and hand movements predominate a number of our interactions in reachable space and yet few studies examine the potential contribution of tactile feedback in planning these actions. This thesis was designed to investigate eye and hand coordination during movement sequences when reaching out to interact with objects. We developed a virtual reality paradigm that allowed us to control visual, tactile, and in some cases, auditory feedback provided to participants. Participants reached and touched five objects in succession. We measured behaviour that resulted from removing one or more of the aforementioned sources of feedback – focusing on task accuracy, and the timing and dynamics of eye and hand movements. Our principle manipulations were to remove visual feedback of the hand, and/or to change the object response to contact. We also unexpectedly removed tactile feedback signaling contact. In Experiment 1, we examined gaze and hand movement timing relative to contact events. Gaze remained long enough to capture contact in central vision, but also followed a time course indicating that contact timing was predicted. In Experiment 2 we examined the influence of dynamic object consequences (i.e., motion). Gaze remained to monitor consequences that follow initial contact especially when the hand was invisible; with longer delays it became difficult to differentiate between predictive or reactive movements. In Experiment 3 we directly tested whether gaze would hold upon a site of action during prolonged manipulation. Here, gaze remained past contact time and instead its departure was associated with the completion of action. Our findings are congruent with the notion that visually guided reaches are controlled to facilitate directing the hand to viewed locations of action – without visual feedback of the hand accuracy diminished and hand approach changed across all experiments. However, we provide consistent evidence that gaze is also controlled to capture planned sensory consequences related to action at its viewed location. Monitoring these sites would facilitate comparing predicted sensory events with those that are actively measured and improve control throughout the movement sequence. Such a process also indicates the importance of considering tactile feedback when examining coordinated eye and hand movements. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2009-11-13 16:12:30.086

One enduring question in the study of speech concerns the nature of the link between speech perception and production. Although accumulating evidence suggests that these two facets of spoken language are tightly coupled, the cognitive structure and neural organization underlying the interactions between the two processes are not well understood. In this thesis, I focus on questions that arise from observations related to when individuals are both talking and listening, and assess the sensitivity of talkers and listeners to the same change in the acoustics of speech. First, I aim to elucidate the neural substrates of auditory feedback control during vocalization by examining the brain response to acoustic perturbations towards auditory concomitants of speech using functional magnetic resonance imaging (fMRI) (Chapters 2 and 3). I demonstrate, for the first time, an extensive network of brain regions involved in the detection and correction of auditory feedback errors during speech production, for which three functionally differentiated neural systems can be delineated. Then I set out to address the online perception of own voice identity as individuals are talking. Chapters 4 and 5 measure the perceptual sensitivity of individuals to the auditory concomitants of their own speech by presenting temporally gated auditory feedback in stranger’s voices during talking. The results show that people perceive stranger’s voices as a modified version of their own voice and adjust their vocal production accordingly, when their utterances and heard feedback are phonetically congruent. Chapter 6 further examines this perceptual effect by using experimental paradigms in the domain of body ownership and shows that the misattribution of the stranger’s voice, is not predicted by individual differences in suggestibility; rather it is related to the integration of multimodal cues. In summary, by focusing on how the acoustics of speech are simultaneously processed for both the perception and production sides of spoken language, the series of studies add significantly to our understanding of the psychophysical, cognitive and anatomical relationships between speech perception and production, and are relevant to a wide range of clinical pathologies (e.g., stuttering, schizophrenia). / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2012-08-29 10:08:57.516

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

This thesis investigates the processes of human postural control. How do we keep still? In any action, the force required changes with limb position. This force-position relationship is elastic stiffness. Holding a desired posture requires muscle activation that accounts for this load property. The studies here examine the physiological processes of postural control as elastic stiffness changes. Psychophysical studies show that thresholds for detecting differences in load stiffness are large relative to those normally encountered. To discriminate stiffness, subjects made consistent movements and judged the force required and detection thresholds followed rules for force perception. For the purposes of postural control, stiffness per se is not a variable of primary interest. The effects of load stiffness on postural stability were investigated using a pendulum that allowed independent control of load force and stiffness. Postural stability varied with load stiffness and this effect was independent of load force. Performance deteriorated as load stiffness became more negative. Load-dependent changes were at low frequencies only, suggesting neural processes operating at long latency, and perhaps ???volitional??? tracking, are the key to postural control. Imposed perturbations evoke patterns of muscle activation reflecting the state of the neural pathways of postural control. Stretch responses obtained while subjects held different loads show that the short-latency spinal reflex and the long-latency functional reflex in the active flexor muscle are unaffected by load stiffness. However, a stereotyped response observed after stretch-reflex latency varied systematically with load stiffness, as did reciprocal activation of the antagonist extensor muscle. The long-latency reflex appears to be a part of a coordinated reciprocal response of antagonist muscle pairs. Adapting to load properties involves modulating these later neural responses. A method was developed, based on ultrasound, to track changes in muscle and tendon length associated with small postural movements. The relationship between wrist angle and muscle and tendon length in the active muscle changed with load stiffness. Particularly with negative-stiffness loads, the wrist moves on the end of a compliant tendon without corresponding changes in muscle length. Thus, compensation of postural performance by neural modulation is limited by the properties of muscle and tendon.

abstract: This study examines cognitive and motor function in typical older adults following acute exercise. Ten older adults (Mage = 65.1) completed a single session of assisted cycling (AC) (i.e., exercise accomplished through the use of a motor), voluntary cycling (VC) (self-selected cadence), and a no cycling (NC) control group. These sessions were randomized and separated by approximately one week. Both ACT and VC groups rode a stationary bicycle for 30-minutes each session. These sessions were separated by at least two days. Participants completed cognitive testing that assessed information processing and set shifting and motor testing including gross and fine motor performance at the beginning and at the end of each session. Consistent with our hypothesis concerning manual dexterity, the results showed that manual dexterity improved following the ACT session more than the VC or NC sessions. Improvements in set shifting were also found for the ACT session but not for the VC or NC sessions. The results are interpreted with respect to improvements in neurological function in older adults following acute cycling exercise. These improvements are balance, manual dexterity, and set shifting which have a positive effects on activities of daily living; such as, decrease risk of falls, improve movements like eating and handwriting, and increase ability to multitask. / Dissertation/Thesis / Masters Thesis Exercise and Wellness 2015

No description available.

No description available.

No description available.

No description available.