Thesis (Ph. D.)--University of Rochester. Dept. of Biomedical Engineering, 2009.The auditory system operates in an interactive multi-sensory setting and its
representation of space is influenced by physiological and environmental factors. To
obtain a useful depiction of acoustic space, the brain must interpret auditory spatial
cues within the context of these factors and appropriately co-register auditory space
with other sensory modalities. A dependable multi-sensory map of the external world
is crucial for successfully navigating through, interacting with, and surviving in the
environment.
The goal of this thesis was to identify, re-evaluate, and elaborate on auditory
and non-auditory factors that impact two-dimensional sound localization in humans.
The influence of (1) elevation cues, (2) static eye position, and (3) sensori-motor
context (pointing method) on auditory spatial processing was evaluated behaviorally.
In Part 1, elevation cues, arising mainly from spectral filtering by the external ear, are
shown to also impact sound localization in azimuth, which depends on interaural
difference cues. Therefore, elevation cues potentially contribute to azimuth accuracy
to correct errors inherent to the geometry of interaural cues.
In Part 2, evidence is put forth to demonstrate that sound localization adapts to
eccentric eye position. The adaptation develops exponentially over time, reaches a
maximum within ~1 minute, spans two-dimensional frontal space, and is
accompanied by a concurrent adaptation in perceived straight ahead. These findings
help reconcile inconsistent reports on this issue in the sound localization literature,
and may also have bearing on spatial adaption to vision displaced by optical prisms. In Part 3, head (or nose) pointing under different sensori-motor contexts
reveals that gaze (eye and head) is a more accurate and precise measure of target
location than either head or eye position alone. This underscores the importance of
quantifying perceived target location using eye in addition to head position even
when subjects are specifically instructed to use head pointing.
In conclusion, this thesis demonstrates that two-dimensional sound
localization is sensitive to a variety of previously unrecognized or poorly
characterized physiological factors. These factors have important implications about
coordination of spatial information across multiple senses, limitations in
methodologies used to study sound localization, and interpretation of data reported by
past studies