Behavioral and fMRI Measures of Crossmodal Plasticity Induced by Auditory Sensory Substitution

Citation

Stiles, Noelle Rebecca Barry (2015) Behavioral and fMRI Measures of Crossmodal Plasticity Induced by Auditory Sensory Substitution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9N29TZP. https://resolver.caltech.edu/CaltechTHESIS:11072014-145237990

Abstract

Thirty nine million people are blind worldwide. Sensory Substitution (SS) attempts to aid the blind by translating images into sound and thereby restoring visual function. Previous studies have found that training on SS generates crossmodal neural changes allowing for activation in early visual regions in response to SS sounds. Unfortunately, training on auditory sensory substitution to become proficient at basic visual tasks takes 1 week to 3 months and even then is slow, inaccurate, and attention-intensive. In this thesis it was studied if SS interpretation could be performed by entirely naive users automatically, and if the crossmodal plasticity engendered through training could be engaged automatically. In contrast to the top-down SS interpretation, we have found that SS interpretation can be effortless and automatic in entirely naive individuals when crossmodally intuitive stimuli that contain crossmodal mappings are used. Crossmodal mappings are pre-existing associations in all individuals of images and sounds that were found to be used for entirely naive interpretation of SS. This result indicates that SS could potentially be made more useful to the blind with appropriate training and translation algorithms. We also studied if the crossmodal plasticity generated by SS training can also be activated automatically in trained blind and sighted device users. We found that crossmodal plasticity engendered through a week of training could be triggered automatically by SS stimuli. This indicates that crossmodal plasticity does not require an attention-intensive task be used and therefore is not entirely top-down cognitive. It might be possible to tap into this automatic processing in visual cortex of SS stimuli to make SS interpretation less effortful and more perceptual following the appropriate training. Overall, this thesis attempts to use SS to understand crossmodal neural processing and plasticity, and to through this broadened knowledge restore some visual function to the entirely blind.

Thesis Files