~ICMC 2015 - Sept. 25 - Oct. 1, 2015 - CEMI, University of North Texas
Binaural Navigation for the Visually Impaired
with a Smartphone
Lee Tae Hoon
NUS High School
10910080@gmail. com
Manish Reddy Vuyyuru
NUS High School
wildtangles@gmail. com
T Ananda Kumar
NUS High School
[email protected]
Simon Lui
Singapore University of
Technology and Design
simon
[email protected]
ABSTRACT
We aimed to determine the feasibility of binaural navigation
and demonstrate piloting of blindfolded subjects using only
recorded (virtual) binaural cues. First, the localization accuracy, sensitivity to angular deviations and susceptibility to
front-back confusion of the subjects was measured using setups modified from previous works on localization capacity.
Afterwards, a software prototype that seeks the relevant binaural cues from a database to keep a subject on a predetermined path by determining the subject's head orientation and
coordinates was developed on the Android platform. It was
scored by the root-mean-squared deviation (RMSD) of blindfolded subjects from the route. Experimental results show
that precise piloting of blindfolded subjects is achievable using only virtual binaural cues. We also discuss the growing
potential for more sophisticated uses of binaural media.
1. MOTIVATION
The ability to deduce the location of a sound source from auditory cues (localization) is a behavioral instinct developed
upon birthl'I. By recruiting the visual cortex in the context of
localization, the visually impaired process auditory cues better than people without any visual impairmentl2'. However,
outdoor navigation via environmental cues is still remarkably
difficult for them. Since audio navigation systems for the visually impaired rely primarily on verbal instructions instead of
spatial audio localization 13141151, the investigation was initiated to explore and develop the feasibility of recorded (virtual) binaural cues for indoor and outdoor navigation.
2. BACKGROUND
Three main auditory cues are responsible for auditory localization - interaurl intensity differences (IID), interaural time
differences (ITD) and monoaural spectral cues (MSC). IID
and ITD account for sound localization laterally (left, ahead,
right). The sound received at the contralateral ear is shadowed by the head and results in IID. The cue is more profound for higher frequencies where the wavelength of the
sound is smaller than the distance between the two ears
(>1600Hz). The arrival time delay from the physical separation of the ears on the head results in ITD and is more profound for sounds of lower frequencies (<1600Hz)161. MSC
Copyright: ~ 2015 Lee Tae Hoon et al. This is an open-access article
distributed under the terms of the Creative Commons Attribution License
3.0 Unported, which permits unrestricted use, distribution, and reproduction
in any medium, provided the original author and source are credited.
account for sound localization in the median plane (front,
above, back, below). MSC arise from the differences in the
way sounds interact with the head, torso, pinna and ear canal
of the listener.
3. OVERALL METHODOLOGY
30 subjects were selected from an initial pool of volunteers
after screening against hearing disabilities using standard
hearing tests. Subjects' heads were centered at the origin. Angles to a subject's left from the nasal axis are defined as positive and vice versa (see Figure 1). Markers were laid at specific angles at a 1.5m radius from the origin. A 0.500s metronome click covering the frequency spectrum from 500Hz to
5000Hz was played over a 100mm diameter speaker levelled
to the seated subjects' ear levels as the audio stimulus. An
individualized spatial audio database of virtual binaural cues
was built by recording clicks played from the marked positions with in-ear binaural microphones for every subject. The
MS-TFB-2-80049 ultra-low noise microphones were small
and in-ear, thus capturing MSC without disturbing the anthropometry of the external features, and binaural, thus capturing both ITD and IID.
4. ABSOLUTE LOCALIZATION
Deviation
Measured
750
90
0~
2
-60
\ Irteraural Axis -96
I
Figure 1. Setup of Experiment 1
4.1 Method (Real Sound Source)
The audio stimulus was played from the reference angles 750,
550, 100, -350 and -650 at a radius of 1.5m from the origin.
The angles were purposefully picked from the frontal azimuth since subjects instinctively turn to face sounds coming
from the back before attempting to pinpoint the source. Subjects, unaware of the reference angles, were tasked to point a
laser at the source after exposure to each audio stimulus. The
laser then lands on a sheet of paper arched into a semi-circle
of radius 1.8m from the origin positioned at the height of subjects' torsos to capture localization data. The subjects were
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