Psychoacoustics can be defined simply as the psychological study of hearing. The aim of psychoacoustic research is to find out how hearing works. In other words, the aim is to discover how sounds entering the ear are processed by the ear and the brain in order to give the listener useful information about the world outside.
The connection of psychoacoustics with psychology can be misleading, as I have discovered over and over again while trying to describe my job at parties. Many of the problems approached by psychoacousticians have very little to do with what the popular conception of psychology. For example, some of my own research has been concerned with how the loudness of sounds is represented by nerve cells in the ear. Some might imagine that this would be a concern of neurophysiology, and indeed it is. However, whereas an auditory physiologist might approach the problem by sticking an electrode into a hapless rat, a psychoacoustician would approach the problem by measuring the ability of human listeners to make discriminations between carefully chosen sounds presented over headphones. The fact that we measure the behavioural responses of human listeners is essentially why psychoacoustics is regarded as a branch of psychology.
Psychoacoustics is not concerned with how sounds produce a particular emotional or cognitive response. We leave this esoteria to the cognitive psychologists and stick to the basics. Having said that, psychoacoustics is a very broad area, and while there is a large overlap with physiology at one end, at the other end we sometimes have to appeal to mainstream psychology in order to account for our more complex experimental results.
Some of the hot areas of psychoacoustic research at the time of writing are:
How do we separate sounds occurring simultaneously (e.g. two speakers speaking at once)?
How do we localise sounds in space?
How do we determine the pitch of, say, a musical instrument?
Thrilling stuff, eh?
Note: researchers in this field are properly called psychoacousticians and they should not be confused with the infinitely more dangerous psycho acousticians who have a tendency to stab people in the back with tuning forks.
What is Psychoacoustics Useful?
Many readers might be disappointed at this point to discover that psychoacoustics is not about sonic mind control, although if you have ever done one of my experiments you might appreciate the effect of extreme boredom on the will to live. Despite the rather dry account of our activities I have given so far, psychoacoustics really does have something of importance to offer society at large.
Determining the abilities and limitations of human hearing is invaluable in helping us to use sounds in our environment. Any device that produces sound for the purpose of human listening should take account of what the listener's ears are going to do with that sound. Some of these design imperatives are little more than common sense, or can be dealt with by a casual listening test. In many cases, however, a deeper knowledge is required. For example, how would you design a data compression device that reduces the amount of digital information travelling down a phone line without affecting perceived sound quality? How would you determine a safe or comfortable level of noise exposure at a factory? How would you design an auditory warning system that is clearly audible above the background noise without being distracting? A working knowledge of psychoacoustics can be a great help in all these design problems.
One very important application of psychoacoustics for many people is in helping the hearing impaired. Although conventional hearing aids, which are basically just electronic amplifiers, help their users hear quiet sounds, they are in many cases worse than useless in situations where there is lot of competing sounds, such as in a crowded room with many people speaking at once. In these situations, the competing sound is amplified just as much as the sound of interest and no advantage is obtained from the aid. Researchers such as Brian Moore at the University of Cambridge are using their measurements of the limitations associated with hearing impairment in order to design the next generation of hearing aids. These aids will help listeners "hear out" the sounds that are of interest to them. Without a thorough knowledge of the psychoacoustics of hearing impairment such design would be by trial and error. With the appropriate information, however, it is possible to design an aid that can compensate directly for the individual's specific disability.
Why is Psychoacoustics Interesting?
Human beings are naturally very curious creatures. We like to know why things are the way they are. Sounds are so important to us in so many different areas that one might expect a great deal of interest in why we perceive sounds in the way that we do. To be honest, however, many psychology students run screaming from lectures in hearing. I believe this is more to do with the frequently technical nature of the subject matter than a lack of desire to learn about hearing. This is a shame because the basic findings of psychoacoustics can be understood without a detailed background knowledge.
