Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Neuroscience

Supervisor

Dr. Melvyn A. Goodale

Abstract

Some blind humans use the reflected echoes from self-produced signals to perceive their silent surroundings. Although the use of echolocation is well documented in animals such as bats and dolphins, comparatively little is known about human echolocation. The overarching goal of the work presented in this thesis was to shed light on some of the basic functions of human echolocation, including the perception of the shape, size, and material. I addressed these aspects of echolocation using behavioural psychophysics and neuroimaging.

In Chapter 2 I show that blind echolocators were able to accurately identify the shape of 2D objects, but that their ability to do so was dependent on the use of head and body movements to ‘scan’ the objects’ edges. I suggest that these scanning movements may be similar to the many saccades made by sighted individuals when visually surveying an object or scene.

In Chapter 3 I addressed the possibility that object size perception via echolocation shows size constancy – a perceptual phenomenon associated with vision. The results revealed that an expert echolocator accurately perceived the true physical size of objects independent of their distance, even though changes to distance directly affect size-related echo information. The results of this study highlight the ‘visual’ nature of echolocation, and suggest further parallels between the two modalities than previously known or theorized.

Chapter 4 presents the results of a functional neuroimaging study aimed at uncovering the neural correlates of material processing via echolocation. By having echolocators listen to recordings of echoes reflected from surfaces of different materials, I show not only that they can determine the material properties of objects, but also that the neural processing underlying this ability may make use of a visual- and auditory-material processing area in the parahippocampal cortex.

Taken together, the work presented in the current thesis describes some of the recent contributions to our understanding of human echolocation, with a particular emphasis on its apparent parallels with vision and visual processing. The results of this work show that accurate and reliable information can be extracted from echoes, thus supporting echolocation as a viable resource for the blind.

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