"An Investigation into the Perceived Urgency of Auditory Warnings
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This thesis considers the perceived urgency of sound, with specific reference to auditory warning design. Psychophysical techniques were investigated as a means of measuring perceived urgency. The biases inherent in different techniques were reviewed. Free modulus magnitude estimation, fixed modulus magnitude estimation, category estimation and cross modality matching were used to scale perceived urgency. On the basis of the cross modality matching validation procedure It was recommended that free modulus magnitude estimation or cross modality matching were used to measure perceived urgency. The successful application of psychophysical techniques meant that the relationship between perceived urgency and objective changes in sound parameters could be quantified. The effects of changes in four different acoustic parameters, speed, pitch, repetition and Inharmoniclty were investigated and quantified. It was shown that increases in all the parameters increased perceived urgency. The amount of change In each parameter that was required to communicate a unit change In perceived urgency was revealed. An attempt was made to see what it was about different acoustic changes that resulted in changes in perceived urgency. In particular, perceived duration was considered as a determinant of perceived urgency. Acoustic parameters were varied in ways known to alter perceived urgency and the effect of these variations on perceived duration was noted. It was shown that one parameter change known increase perceived urgency, increases in speed. Increased perceived duration whereas another, increasingly unresolved stimuli, decreased perceived duration. The Reiss Jones(1989) model of temporal contrast was used to explain these findings. It was suggested that changes in perceived duration were part of what makes changes in acoustic parameters communicate changes in perceived urgency. The nature of the relationship between perceived duration and perceived urgency may depend on the type of acoustic parameter used to communicate urgency.
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