Thesis (M.Eng.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2008/05/13). Includes bibliographical references.

Proefschrift Universiteit Maastricht. / Met lit. opg. - Met samenvatting in het Nederlands.

Note:

Thesis (Ph. D.)--University of Chicago, Committee on Neurobiology, March 1999. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 127-162).

No description available.

No description available.

<p> This dissertation investigated the importance of information from various sensory receptors on the perception of self-orientation. In five experiments, we systematically manipulated the relative orientation between the gravitational inertial forces and the body. </p> <p> The first experiment was originally designed to evaluate the effect of body inversion on the perception of straight-ahead. Interestingly, when participants were inverted, females presented a greater footward bias in the perception of straight-ahead than males. Two follow-up experiments revealed that whole-body rotation and altered blood-distribution could not explain the gender differences in the perception of straightahead. As a result, we attributed the gender differences in the perception of selforientation to differences in the use of afferent information from stable gravireceptors (i.e., otoliths). </p> <p> A fourth experiment examined the contribution of perceptual strategy to the perception of self-orientation. Once again, females exhibited a greater footward bias than males in the perception of straight-ahead. However, this bias was reduced slightly when female participants were instructed to focus on cues arising from inside the body. This finding indicates that, at least to some extent, strategy mediates gender differences in perceptual decision-making. </p> <p> The final experiment was designed to examine the importance of limb movement on the perception of spatial orientation. Five response modes were used to gradually increase the motor demands associated with perceptual judgments about self-orientation. This study was designed to test a theory of visual information processing (i.e., Milner & Goodale, 1995), which claims that the use of distinct visual processing modules depend on the motor demands of a visual perception task. Interestingly, we found that whole limb movements affect the perception of an egocentric illusion (i.e., oculogravic illusion; see Graybiel, 1952). </p> / Thesis / Doctor of Philosophy (PhD)

Master of Science in Medicine / Saccadic and vestibular-evoked eye movements are similar in that their three-dimensional kinematic properties show eye position-dependence. When the line of sight is directed towards an eccentric target, the eye velocity axis tilts in a manner that depends on the instantaneous position of the eye in the head, with the magnitude of tilt also depending on whether the eye movement is saccadic or vestibular-evoked. The mechanism responsible for producing eye velocity axis tilting phenomena is not well understood. Some authorities have suggested that muscle pulleys in the orbit are critical for implementing eye velocity axis tilting, while others have suggested that the cerebellum plays an important role. In the current study, three-dimensional eye and head rotation data were acquired, using the magnetic search coil technique, to confirm the presence of eye position-dependent eye velocity axis tilting during saccadic eye movements. Both normal humans and humans with cerebellar atrophy were studied. While the humans with cerebellar atrophy were noted to have abnormalities in the two-dimensional metrics and consistency of their saccadic eye movements, the eye position-dependent eye velocity axis tilts were similar to those observed in the normal subjects. A mathematical model of the human saccadic and vestibular systems was utilized to investigate the means by which these eye position-dependent properties may arise for both types of eye movement. The predictions of the saccadic model were compared with the saccadic data obtained in the current study, while the predictions of the vestibular model were compared with vestibular-evoked eye movement data obtained in a previous study. The results from the model simulations suggest that the muscle pulleys are responsible for bringing about eye position-dependent eye velocity axis tilting for both saccadic and vestibular-evoked eye movements, and that these phenomena are not centrally programmed.

The vestibulo-ocular reflex (VOR) is a simple reflex that stabilizes gaze by moving the eyes in the opposite direction to the head. The gain of the VOR (ratio of head to eye velocity) can be increased or decreased during motor learning. It is thought that the memory for learned changes in the VOR gain is initially encoded within the cerebellar flocculus. Furthermore, these learned gain changes can be disrupted or consolidated into a long-term memory. In this thesis we describe novel results that show that consolidation of the VOR can take place rapidly, within 1 hour after learning has stopped. Furthermore, we demonstrated that unlike learning, which has been shown to have frequency selectivity, disruption and rapid consolidation generalize across the range of frequencies. We suggest that disruption and rapid consolidation in the VOR are local mechanisms within the cerebellar cortex, and do not require new learning. This thesis also provides additional evidence for the idea that learned gain increases and decreases are the result of separate mechanisms, most likely long-term depression and potentiation respectively, at the parallel fibre-Purkinje cell synapses. We demonstrate that learned gain increases, but not decreases, require the activation of type 1 metabotropic glutamate receptors (mGluR1) and B type γ-aminobutyric acid (GABAB) receptors. Blocking one or both of these receptors with an antagonist inverts gain-up learning, while the agonist augments gain-up learning. Furthermore, we provide novel evidence that these receptors are co-activated during gain-up learning.