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Title: Investigation of acoustic cues used by humans to identify the spatial position of an object based on echoes
Author: Edwards, David Steven
ISNI:       0000 0004 2729 2111
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2012
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Echolocation involves obtaining information on an object by analysis of echoes reflected from it when an outgoing emission is directed towards it. This study investigates human ability to determine the left-right position of an object using echolocation in a specific set of conditions. Previous literature demonstrated that echolocation can be used to identify the spatial position of an object, though the acoustic cues used to achieve such a task have not been identified. Understanding whether subjects are able to use binaural cues for such a task is important because, if they can, then the determination of spatial position via echolocation can be generalised to real-life conditions. Furthermore, ISVR pilot studies have demonstrated that subjects may have had access to additional echolocation cues in previous studies. This study investigates the ability of subjects with minimal (procedural) training to determine the left-right position of an object in 'virtual echolocation' experiments in which cues unrelated to echoes from the emission were eliminated. Impulse response measurements taken when an emission was directed at a board positioned at 17· to the ears of an acoustic mannequin, KEMAR, were analysed and combined (convolved) with emission signals. Convolved stimuli were presented to subjects via insert earphones in three psychoacoustic experiments conducted by the author. Experiment 1 used 18 subjects to examine sensitivity at 0.9 m using broad band stimuli of 10-400 ms, showing that sensitivity increased with signal duration. By windowing out the start of each signal, it was also shown that the precedence effect, which generally reduces a subjects' sensitivity to binaural cues within echoes, does not affect ability at the distance measured. The experiment also demonstrated that small changes to board position could have dramatic effects on information useable within the echo, explaining why many subjects have been observed moving their heads when echolocating, a technique known as 'head scanning'. A set of 13 subjects were common to experiments 2 and 3, with participants using 400 ms-duration stimuli to identify board position. Experiment 2 showed sensitivity above chance levels for echolocater to object distances of 0.6 to 1.2 m using broadband stimuli. Experiment 3 applied diotic presentation and level-roving to examine whether subjects relied on non- binaural cues at 0.9 m. Frequency-filtering isolated any binaural cues used. Results indicated that high-frequency interaural level difference (lLD) was the main cue, though 2 trained musicians showed some ability to use non-binaural cues. It is concluded that subjects with minimal training can use echolocation to determine the left-right spatial position of a large reflective object placed at a 17 degree angle from them based primarily on high-frequency lLD, at least at a distance of 0.9 m. Thus, it should be possible to identify spatial position of an object outside of the laboratory via echolocation. Furthermore, increased sensitivity with duration indicates that subjects should try to maximize energy in their emission signal when echolocating. Further work should be conducted to isolate the acoustic cues used in other echolocation tasks and the virtual technique piloted here provides a mechanism for doing so.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available