Sound localisation is a complex perceptual process that involves the integration of
information derived from multiple audible cues. Human sound localisation is mediated
by these audible cues. The primary audible cues are the interaural time difference (ITD),
phase difference (IPD) and intensity difference (IID) that result from diffraction of sound
waves around the head and pinnae. The ITD and the IID have received much attention
in the literature as they are considered to be the most important binaural cues. These cues
result from a neural comparison between the signals at both ears. Although these cues
are signal-dependent, they have not been investigated using day-to-day life signals due to
the experimentation complexity. Many research studies employed either single frequency
or unnatural signals to draw conclusions. Further, the IPD could not be distinguished
from the ITD for multiple frequency signals.
This thesis presents new experimental techniques which are developed to investigate the
role of primary audible cues in sound localisation. These techniques independently
control and investigate the cues with multiple frequency signals. Listening experiments
are initially completed with single cues which are followed by experiments with cues in
conflict. The stimuli are chosen to include representative day-to-day life signals. Two
audible cues at a time are used simultaneously in conflict so that their relative importance
can be determined. Experimental techniques included a mathematical approach to
manipulate the phase of all the component frequencies in a multiple frequency signal,
whilst leaving the amplitude structure unchanged. This approach is adopted to
distinguish the IPD from an equivalent ITD for multiple frequency signals. It is therefore
possible to investigate the IPD independently with multiple frequency signals. The
experimental results indicate that the effect of the IPD can be compensated for by an
appropriate opposing ITD. In general, localisations become centrally diffuse when either
the ITD or the IPD is placed in conflict with the IID.
A localisation model is developed to provide predictions for the effect of one cue against
an alternative cue, similar to the experiments. The results from the model are in
agreement with the experiments. It is not evident whether the ITD or the IPD is more
effective.
The new techniques and the localisation model provide the opportunity to investigate the
primary audible cues with representative day-to-day life signals. It has become possible
to independently assess these cues and to draw conclusions based on their role in sound
localisation.
An advance on the auralisation results previously presented for interaural time and intensity conflict cue experiments is reported by the inclusion of phase for multiple frequency tone bursts and wideband signals. A method is presented to manipulate the phase of all the component frequencies in a wideband signal whilst leaving the amplitude structure unchanged through the use of the Hilbert transform. Therefore phase and time become distinguishable from each other for such signals. The results indicate that localisation remains strong in the presence of large phase shifts. Furthermore the central diffuse field that is characteristic of intensity versus interaural time conflict experiments is absent when the intensity and phase of wideband signals are placed in conflict
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