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No description available.

No description available.

The purpose of the present research was threefold: 1) to investigate whether natural aging affects the movements to remembered targets when participants make reaching movements under closed-loop feedback conditions, 2) to determine if experience with visually-guided movements facilitates memory-guided reaching and 3) to determine if age affects this facilitation. Two groups of 10 participants (healthy older and healthy younger) performed a manual aiming task with a mouse on a graphics tablet. A target appeared in one of 6 possible locations on a computer screen and participants had to make aiming movements with a visible cursor in 3 different visual conditions: full vision, immediate recall and delayed recall. In the full vision condition vision of the target was available throughout the movement. In the delay conditions the target disappeared either at the initiation of the aiming movement (immediate recall) or 2 seconds before movement onset (delayed recall). Vision of the hand (cursor) was available in all conditions. Each memory condition was divided into 2 blocks; block 1 was presented before the full vision condition and block 2 was presented after. Endpoint accuracy and variability were measured along with movement kinematics. Results showed no age differences in the kinematics in the full vision condition. For memory dependent pointing age also did not affect the movement kinematics or endpoint accuracy. Movements to remembered targets were significantly more variable in the delay recall compared to the immediate recall condition. A Block by Condition effect showed that the delay effect was present in the first block, but not in the second block, suggesting that variability did not increase with memory delay once participants had experience from full vision reaching. A Group by Condition effect showed the older adults were more variable than younger, although this difference was smaller in the delay condition due to the increase in variability as a function of delay seen in younger but not older adults. These findings suggest that aging does not affect how movements are controlled whether pointing to visible or remembered targets. They also suggest that aging does not affect the accuracy in pointing to remembered targets. Aging does affect the variability of these pointing movements. Finally, experience in pointing at targets with full vision modulates the increase in variability of pointing as a function of delay.

The purpose of the present research was threefold: 1) to investigate whether natural aging affects the movements to remembered targets when participants make reaching movements under closed-loop feedback conditions, 2) to determine if experience with visually-guided movements facilitates memory-guided reaching and 3) to determine if age affects this facilitation. Two groups of 10 participants (healthy older and healthy younger) performed a manual aiming task with a mouse on a graphics tablet. A target appeared in one of 6 possible locations on a computer screen and participants had to make aiming movements with a visible cursor in 3 different visual conditions: full vision, immediate recall and delayed recall. In the full vision condition vision of the target was available throughout the movement. In the delay conditions the target disappeared either at the initiation of the aiming movement (immediate recall) or 2 seconds before movement onset (delayed recall). Vision of the hand (cursor) was available in all conditions. Each memory condition was divided into 2 blocks; block 1 was presented before the full vision condition and block 2 was presented after. Endpoint accuracy and variability were measured along with movement kinematics. Results showed no age differences in the kinematics in the full vision condition. For memory dependent pointing age also did not affect the movement kinematics or endpoint accuracy. Movements to remembered targets were significantly more variable in the delay recall compared to the immediate recall condition. A Block by Condition effect showed that the delay effect was present in the first block, but not in the second block, suggesting that variability did not increase with memory delay once participants had experience from full vision reaching. A Group by Condition effect showed the older adults were more variable than younger, although this difference was smaller in the delay condition due to the increase in variability as a function of delay seen in younger but not older adults. These findings suggest that aging does not affect how movements are controlled whether pointing to visible or remembered targets. They also suggest that aging does not affect the accuracy in pointing to remembered targets. Aging does affect the variability of these pointing movements. Finally, experience in pointing at targets with full vision modulates the increase in variability of pointing as a function of delay.

It is all but universally accepted in epistemology that knowledge is factive: S knows that p only if p. The purpose of this thesis is to present an argument against the factivity of knowledge and in doing so develop a non-factive approach to the analysis of knowledge. The argument against factivity presented here rests largely on empirical evidence, especially extant research into visuomotor noise, which suggests that the beliefs that guide everyday motor action are not strictly true. However, as we still want to attribute knowledge on the basis of successful motor action, I argue that the best option is to replace factivity with a weaker constraint on knowledge, one on which certain false beliefs might still be known. In defence of this point, I develop the non-factive analysis of knowledge, which demonstrates that a non-factive constraint might do the same theoretical work as factivity.

Recently, researchers have found evidence that after a concussion, residual visuomotor control deficits may linger longer than working memory or psychomotor speed deficits. All of the major computer administered test batteries currently in use for concussion management rely on examination of the latter tasks, and lack any measure of visuomotor control. The present research set out to develop a task to measure visuomotor performance. Using a touch-screen computer, the task required participants to point towards or away from (i.e., antipointing) a target in a design simmilar to an anti-saccade task. The task required participants to use visual information to execute controlled movements, and is designed to measure movement planning, execution performance and accuracy. The task was delivered to a large sample of healthy individuals to develop a normative performance data set. A self-report questionnaire was used to identify a small group of individuals from the normative population who were identified with a prior history of concussion. These individuals were directly contrasted with the healthy individuals. While only a few reported moderate or severe concussions, and information about recency and number of occurrences was unavailable, performance differences were observed --providing evidence of residual deficits. In particular, while concussed individuals were not slower, or less accurate overall than the healthy population on the task, they demonstrated unusual hand and spatial asymmetries. Future research will compare recently concussed individuals with the normative set developed here, and will make direct comparisons with existing computer administered test batteries to determine the efficacy of visuomotor tasks for detecting the long-term effects of concussion.

Recently, researchers have found evidence that after a concussion, residual visuomotor control deficits may linger longer than working memory or psychomotor speed deficits. All of the major computer administered test batteries currently in use for concussion management rely on examination of the latter tasks, and lack any measure of visuomotor control. The present research set out to develop a task to measure visuomotor performance. Using a touch-screen computer, the task required participants to point towards or away from (i.e., antipointing) a target in a design simmilar to an anti-saccade task. The task required participants to use visual information to execute controlled movements, and is designed to measure movement planning, execution performance and accuracy. The task was delivered to a large sample of healthy individuals to develop a normative performance data set. A self-report questionnaire was used to identify a small group of individuals from the normative population who were identified with a prior history of concussion. These individuals were directly contrasted with the healthy individuals. While only a few reported moderate or severe concussions, and information about recency and number of occurrences was unavailable, performance differences were observed --providing evidence of residual deficits. In particular, while concussed individuals were not slower, or less accurate overall than the healthy population on the task, they demonstrated unusual hand and spatial asymmetries. Future research will compare recently concussed individuals with the normative set developed here, and will make direct comparisons with existing computer administered test batteries to determine the efficacy of visuomotor tasks for detecting the long-term effects of concussion.

The visual grasp reflex provides automatic orienting of gaze (the visual axis in space) to novel visual stimuli. Previous studies have demonstrated activation of neck muscles of awake monkeys appearing at a short fixed latency (55 to 95 ms) after visual target presentation, regardless of whether or when saccades are made. The purpose of these early visually-driven muscle activations may be to prime head rotation required as a part of the coordinated eye-head movement to the target. Similar orienting responses might be found for visually guided reaching. Here, we explore early visually-driven muscle activations of the human upper limb immediately preceding planar reaching movements. Subjects performed reaches towards small visual peripheral targets while upper limb kinematics were recorded and intramuscular electromyography was collected from four shoulder and elbow muscles. Subjects maintained their right hand at a central fixation marker that was extinguished for a gap period (200 ms) prior to appearance of a peripheral target. Subjects were instructed to reach to the target as quickly as possible. Some subjects exhibited a short burst of muscle activity (about 20 ms duration) time-locked to visual target onset. This burst occurred around 85 ms to 105 ms after target onset and preceded the onset of muscle activity associated with volitional arm motion by about 100 ms. Notably, this burst was dependent on target location: visually-driven muscle activity occurred in right shoulder extensor muscles for rightward targets and was absent for leftward targets. In order to better dissociate the visual burst from volitional motor activity, we employed a delay paradigm. No time-locked muscle activity was present in the delay task either after the target appeared or after the fixation marker was extinguished. This suggests that the visual burst is dependent on the imminence of voluntary movement and the laterality of the target. We conclude that the appearance of a visual target can result in short-latency activity on the arm musculature that is appropriate for orienting the arm to the target. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2007-09-27 09:42:55.337

Numerous studies have investigated motor learning by examining the adaptation of reaching movements to visuomotor perturbations that alter the mapping between actual and visually perceived hand position. The picture of the visuomotor transformation from visual input to motor input that has developed consists of three broad phases: integration of hand and target locations in a common reference frame, calculation of a movement vector between hand and target, and transformation of this movement vector from the common reference frame into motor commands. The process of adapting to a visuomotor rotation is generally viewed as an alteration of the vectorial representation of reach planning. When visual feedback is rotated, the motor and visual directions no longer coincide and the motor command executed is remapped to the subsequent visual direction produced. In the current set of studies, we examined how learning a visuomotor rotation while reaching to a target with a curved hand path generalizes to straight path reaching and novel target directions. We found that there is very little to no generalization of learning between curved reaches and straight reaches when given only endpoint feedback. With continuous visual feedback, we found partial transfer. This suggests that in the absence of visual feedback, the vectorial adaptation hypothesis is insufficient and adaptation to a visuomotor rotation is mediated by the later stages of the visuomotor transformation, when the motor commands specific to the hand path used are being generated. / Thesis (Master, Psychology) -- Queen's University, 2009-04-16 15:42:40.872