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PsychoacousticsPsychoacoustics is the study of the perception of sound. It aims to provide insights into the mechanisms through which sounds entering the ear are processed and utilised to provide the listener with a meaningful picture of their extra-personal space (i.e. the world outside). Sounds convey two important qualities that inform us of the nature of the world, content and location. The ability to extract these qualities from sounds confers a strong evolutionary advantage upon any animal that can accomplish it. Predators need to be identified, located and fled from, while for a potential mate the same information needs to be extracted but a different response needs to be enacted. It follows then, that psycho-acoustical studies can be very loosely grouped in to two separate but related areas: the perception of "what" and the perception of "where". The "what" refers to the perception of a sound’s content. A single sound has many attributes; among them are pitch, loudness and timbre. Many experiments have described in detail the capacity of the auditory system to detect small differences in these qualities: the so called just noticeable differences, eg how small a change in pitch can we detect? The analysis of multiple sounds also falls under the broad banner of the "what". How, in an acoustically busy environment, are we able to listen to a specific conversation and discard all the other auditory stimuli? When we consider that all the sound energy that enters the ear is unseparated and overlapping in frequency, volume and quality, it is easy to appreciate that this is not a trivial problem. Cherry (1953) famously articulated this as the "The Cocktail Party Problem". (See Bregman (2001) for information on Auditory Scene Analysis and a more thorough discussion.) The "where" is concerned with sound source locations. Unlike vision and touch, the receptors for audition are arranged on the basis of frequency, not location. Therefore the establishment of location must be computed not just read from the patterns of receptor activity. Research indicates that cues to horizontal location are mainly found in the differences in sound onset and sound level between ears, and the cues to vertical location come from filtering the incoming sound in a directionally dependent manner by the pinna (external ear). Identical sounds played from different locations around the head will be filtered by the pinna in a manner that reflects the unique location of the sound source. It appears that these spectral cues to location are able to be learnt and then utilised to help isolate a specific location in space. Location and content cannot be considered entirely separately, there is some evidence that location cues can help considerably when solving the Cocktail Party problem and similarly it appears that by separating sounds by source may assist in computing their locations. ReferenceCherry, E. C. (1953). Some experiments on the recognition of speech, with one and two ears. J. Acoust. Soc. Am. 25, 975–979. RecommendedMoore, B. C. J. (2003). An Introduction to the Psychology of Hearing (5th Edition). Academic Press. Summary Written ByJoel Cooper |