Plasticity of the visual system following visual impairment.

摘要

Visual experience shapes the organization of the human visual system early in development, and continues to influence the organization of the adult visual system. Visual impairment modifies visual experience, but its impact on the anatomy and function of the visual system is not well understood. This thesis is an attempt to understand the plasticity of the visual system as a response to visual impairment from a set of brain-imaging and psychophysical studies. Chapter One provides an overview of the thesis. Chapter Two is a review and synthesis of the current state of knowledge on plasticity of early visual areas in the presence of central vision loss. Central vision loss is of special interest because it is frequently a consequence of age-related macular degeneration (AMD), which is the most common cause of vision loss in the United States. The rest of this thesis contains a brain-imaging study of four individuals with central vision loss from AMD (Chapter Three), a psychophysical study of perceptual learning in normal peripheral vision among a group of older observers (Chapter Four) and a brain-imaging study of a visually impaired individual who has a rare ability to read both Braille by touch and print visually (Chapter Five). This set of studies shows that the visual cortex can reorganize as a result of visual impairment. However, this ability to reorganize seems to decrease with advancing age. Reduced plasticity due to aging also explains the diminished benefits from perceptual learning among older observers. The age-deficits in cortical plasticity explain why functional adaptation to central vision loss is often difficult for AMD patients. Understanding the cortical adaptation of the visual system following visual impairment has important and significant applications in rehabilitation, treatments and assistive technologies for people with visual impairment. Design of rehabilitation programs for AMD patients should take into account the reduced cortical plasticity due to aging.