Blind individuals rely on sound to perceive the distal environment much as sighted individuals rely on vision. Although several lines of research point to enhanced auditory capabilities in blind individuals, the precise nature and extent of such capabilities are unclear. Understanding perceptual differences in auditory processing between blind and sighted individuals, and the neurophysiological mechanisms underlying these differences, forms this project's long-range goal. The present proposal brings techniques of human psychophysical measurement and functional magnetic resonance imaging (fMRl) to bear on three topics: a) the quantification of advantages blind individuals may hold for a range of auditory perceptual and cognitive abilities (e.g., discrimination, attention, memory, and knowledge acquisition), b) the relationship between these abilities and the cortical organization in temporal, occipital and parietal cortex areas resulting from blindness, and c) the relationship between age of onset of blindness, auditory skills and cortical organization. Using methods of signal detection, initial studies will measure blind and sighted individuals' ability to detect, discriminate, and attend to both simple (e.g., frequency) and complex features of sound (e.g., timbre, resonance modes). In order to examine the neural systems underlying auditory processing differences in blind and sighted individuals, fMRl studies will adapt the above behavioral tasks to measure the location, volume and intensity of hemodynamic response in the temporal, parietal and occipital cortices. Additionally, we will compare early blind (EB), late blind (LB) and sighted (SC) individuals to examine the effects of early visual experience on functional reorganization of the brain. The fMRl studies will manipulate stimulus complexity and task difficulty to assess their relative contributions to posterior cortical activity. Recent studies have begun to reveal the considerable abilities of the ear to acquire, retain, and retrieve knowledge about the physical attributes of sound-producing objects and the forces that set them in motion. Accordingly, a second set of studies will determine whether EB individuals show learning advantages over LB and SC individuals. This proposal brings together a novel combination advanced psychoacoustic techniques and fMRI in order to clarify the behavioral capacities and neural concomitants of complex auditory processing in both healthy and blind populations. In sum, this research program should shed important light on behavioral and functional changes in auditory processing as a result of visual impairment. Not only can this improve our understanding of normal auditory processing in sighted individuals, but also can suggest new ways in which the blind may compensate for their visual impairment by optimizing their use of expanded auditory capabilities.
| Stevens, Alexander A; Weaver, Kurt E (2009) Functional characteristics of auditory cortex in the blind. Behav Brain Res 196:134-8 |
| Garg, Arun; Schwartz, Daniel; Stevens, Alexander A (2007) Orienting auditory spatial attention engages frontal eye fields and medial occipital cortex in congenitally blind humans. Neuropsychologia 45:2307-21 |
| Weaver, Kurt E; Stevens, Alexander A (2007) Attention and sensory interactions within the occipital cortex in the early blind: an fMRI study. J Cogn Neurosci 19:315-30 |
| Weaver, Kurt E; Stevens, Alexander A (2006) Auditory gap detection in the early blind. Hear Res 211:1-6 |
