This thesis investigates the dynamic characteristics of fast phase eye movements in the Vestibulo-Ocular Reflex (VOR) and their application in vestibular lesion clinics. Eye responses in the VOR consist of alternations between slow phases (eye moves opposite to head) to stablize the eye in space and fast phases to quickly redirect the eye in space. At the end of each fast phase segment, the eye position appears well correlated with head velocity. In contrast to slow phases, fast phases are of quite short duration. Therefore, they must be detected precisely in order to do any further analysis. This thesis reports an improved version of a previous autoregression (ARX) model classification algorithm, to allow automatic classification of fast phase segments or to detect only end points of fast phases. / Results in this thesis demonstrate that the dynamics associated with the fast phase end points present specific patterns. These patterns can be represented as a linear or a cubic equation. In other words, a first-order or third-order polynomial can be fitted to the experimental data by the least square technique. The DC bias of the fitted data shows distinctive ranges for normal subjects and vestibular lesion patients. The asymmetric an non-linear shapes of the fitted curve can also denote a lesion. Other dynamic properties, such as the fast phase segment frequencies or the phase shift between the output eye position and input head velocity, have strong tendencies to differentiate normals from patients. In addition, the characteristics of fast phase beginning points suggest that the initiation of fast phases in independent of any obvious eye velocity or eye position threshold.

In order to investigate if the ERG could be used to monitor the function of the retina as it is adapting to a new luminous environment, we measured the impact of pre-exposure to a bright luminous environment on the electrical response of the retina recorded (1) immediately after closure of this bright background luminance (i.e., at the onset of dark adaptation) and (2) immediately after a reduction of the background luminance from a brighter to a dimmer level. Our experimental approach resulted in highly significant and transient modifications in the amplitudes and in the peak times of most of the ERG components. This study also lead to a reinterpretation of the genesis of the oscillatory potentials as well as of the origin of the Light Adaptation Effect, a not yet explained retinal phenomenon previously reported by several investigators. We believe that our procedure could have a significant clinical value, as it seems to be suggested with our results obtained from two patients affected with congenital stationary night blindness with myopia.

The purpose of this project is to study the role of human color vision in shape processing. We examine the extent to which color vision can contribute to complex shape processing tasks or whether they are accomplished mainly by the achromatic pathways of the brain. We tested normal human visual performance using psychophysical experiments. The stimuli were presented on a monitor and the task of the subject is to indicate whether shape differences in the stimuli have been seen. Each psychophysical trial was run four-to-five times using a two-interval forced choice paradigm. Stimuli were calibrated so that they selectively activate either the achromatic pathways (black & white) pathways or the color (red-green and blue-yellow) pathways of the human brain. The results of the study show that color vision can perform many of the various types of shape discrimination tasks at similar levels to achromatic vision.

<p> The present dual field of view flexible colonoscope can provide both forward view and radial or backward view of the colon to improve detection of cancerous polyps. The colonoscope has its own illumination that illuminates the parts of the colon viewed by imaging optics. The optical system, limited only by the diffraction effects at the exit pupil over the entire visible spectrum, can provide high resolution and is suitable for color imaging. The flexible colonoscope has an on-board sensor at the proximal end of the colonoscope to improve resolution. The proximal end of colonoscope measures only 8 mm in diameter and 20 mm in length. The present colonoscope has the potential to be scaled down to as small as 6 mm inner diameter from the present 8 mm. </p>

Measurements of acquired colour deficits can aid in the detection of certain visual ailments (King-Smith (1991)). Such ailments cause selective deficits among the different neural colour and luminance coding mechanisms at the post-receptoral level. These mechanisms consist of varying combinations of inputs from the three cone types (L, M, S) responsible for phototransduction in the human visual system. An efficient colour test can measure the sensitivities of these mechanisms independently. In order to achieve this, precise estimates of the cone inputs (or cone weightings) to these mechanisms need to be obtained. / We obtained these estimates through measurement of contrast detection thresholds for sinusoidal gratings in 69 different axes in colour space in three normal human subjects. The colour space used (cone contrast space) permitted direct estimation of the cone weightings from the threshold information. We sensitized each mechanism in turn by varying the spatiotemporal properties of the grating. At each spatiotemporal condition, planar and three-dimensional "super-elliptical" fits were made to the threshold data. The cone weightings of the sensitized mechanism were obtained directly from the parameters of these fits. (Abstract shortened by UMI.)

Spatial vision, refers to how the visual system encodes the relationships between simple features in the external world for extraction of meaningful information as to object form and location in space. Amblyopia (from the Greek, meaning "blunt vision") is a developmental monocular deficit arising in an estimated 5% of children and is the most common cause of unilateral blindness in the adult population. The condition is primarily associated with a strabismus (misalignment of an eye) or anisometropia (unequal refractive error in the two eyes) or both (mixed amblyopia) being present at or shortly after birth. The strabismic amblyopic deficit includes a decrease in contrast sensitivity, with an accompanying loss in acuity. This population is unique in that unlike the anisometropic group, they experience spatial distortions and non-contrast dependent anomalous spatial localization. This has led to the proposition that tarachopia or "distorted" vision may be a better descriptive term to use as opposed to amblyopia or "blunt" vision. / In an effort to characterize the distortions that strabismic amblyopes perceive, we have quantified the deficit in spatial localization across the dimensions of spatial scale, eccentricity and exposure duration. The results show that: (1) the deficits of spatial localization, spatial uncertainty (increased alignment threshold) and bias (perceived point of subjective alignment) are uncorrelated; (2) both deficits are scale invariant for well separated elements; (3) the form of the regional distribution depends on the spatial measure used and the scale at which it is measured; (4) there is a poor correlation between the deficit for either spatial measure and the contrast sensitivity loss; and (5) spatial uncertainty is invariant with exposure duration. / In addition we have sought to characterize the neural substrate of the spatial deficits. We psychophysically probe the sampling properties of the neuronal population and analyze the dependence of simple pattern discrimination on stimulus bandwidth properties. Our results show that the detection deficit due to neural pooling is effective in limiting the spatial frequencies where sampling considerations are important. Within this region of visible high frequencies, an irregular arrangement of neurons rather than neural loss is the greater contributor to the strabismic amblyopes' deficit. In addition, the amblyopic eye either has broader orientation and spatial frequency detectors or is deficient only for first-order orientation processing.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1116. Advisers: Jamshid Ghaboussi; David Pecknold. Includes bibliographical references (leaves 120-126) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4306. Advisers: Philip N. Sabes; Stephen G. Lisberger.

Thesis (Ph.D.)--Indiana University, School of Optometry, 2007. / Source: Dissertation Abstracts International, Volume: 68-10, Section: B, page: 6598. Adviser: T. Rowan Candy. Title from dissertation home page (viewed May 20, 2008).

Thesis (Ph.D.)--University of California, San Francisco, 2005. / Source: Dissertation Abstracts International, Volume: 66-02, Section: B, page: 0738. Adviser: Stephen G. Lisberger.