An Introduction to Psychoacoustics
Psychoacoustics, a branch of psychophysics, is the study of how sound and noise psychologically (and, by extension, physiologically) effects people.
Sound is not a purely physical phenomenon. Or it is up until the moment of ‘auditory transduction’, when the organ of Corti sends electrochemical impulses (known as action potentials) through the auditory nerve to the auditory cortex. Once these ‘actions’ are received, we are no longer operating in the field of acoustics or even the field of physics; we are operating in the realms of psychology and neurology.
The distinction between psychological and neurological responses to sound can be difficult to define. A good example of a psychological effect comes from the field of music therapy, arguably one of the most robustly explored areas of psychoacoustics. When we hear a snippet of music from our childhood – a pop song or a television theme tune – a whole host of images and emotions can come flooding from the deeper recesses of our memory. An example of a neurological (even physiological) response has been experienced by anyone who has been to the cinema to watch an action movie. The film’s sound designers manipulate the fine dynamics of sound to artificially trigger the ears’ acoustic reflex (normally reserved for very loud noises) to create the impression that an explosion, for example, is a lot louder than it actually is in reality. If filmmakers where to actually expose the cinema-going public to acoustic-reflex-triggering loud noises, they would find themselves on the receiving end of any number of legal actions.
Mood and Music
That music affects us emotionally will come as no surprise to anyone. In fact, research has shown that the agreeable feelings linked to emotional music are the result of dopamine release in the striatum (comprising a cluster of neuron in the subcortical basal ganglia of the forebrain). This is the part of the brain that plays a crucial role in the anticipation/reward aspect of drug addiction. Social conditioning plays some role in our emotional responses to music. For example, music in a minor key is likely to make us sad, largely because the likes of funeral marches and requiems tend to be in a minor key. There is, however, something in minor key music which is, in a sense, ‘universally sad’. An anthropological study of the Mafa tribe in Northern Cameroon and eastern Nigeria, who had never been exposed to western music, demonstrated that they could tell the difference between happy and sad (major key and minor key) western music, but they were far less effective at doing so than subjects who’d grown up exposed to the western culture musical traditions.
Nails on a Chalkboard
One popular area of study in the field of psychoacoustics is the effect of nails being raked down a chalkboard. Although some people are immune to this phenomenon, most people find it very unpleasant. There is actually a name for this response: grima. Inge Schweiger Gallo of the Complutense University of Madrid, investigated the sensation and concluded it was a more extreme form of disgust that Spanish speakers ‘word-associate’ with “repulsion” “unpleasant sensation” and “shivering” but is only used in relation to experiences like fingernails on a chalkboard, squeaking polystyrene and touching cork or certain types of foam rubber etc. There is actually no word for grima in English.
The brain interprets sound via the ‘Reticular Activating System’, a collection of neurons about the size of your little finger located in the brain stem. In fact, this cluster of nerves interprets all sensory input, with the exception of smell. The Reticular Activating System ‘listens’ all the time, even when you’re sleeping.
One hypothesis for the adverse reaction to the sound of the nails on a chalkboard is that the noise is similar to that of a primate warning shriek (such as a monkey might produce upon sighting a predator). Studies of macaque monkeys and cotton-top tamarin monkeys seem to support this hypothesis. This suggests that our reaction is akin to a fight or flight response and is a residual mechanism from our primate past.
Hyperacusis (sometimes called hyperacousis) is a heightened sensitivity to noise. For some sufferers, this is a minor inconvenience or irritation; for others, it can make everyday activities unbearable. The condition is most typically associated with tinnitus but there are many triggers or contributing factors, including:
- Ménière's disease
- Tay–Sachs disease
- Lyme disease
- Williams syndrome
- Systemic lupus erythematosus
- Multiple sclerosis
- Severe head trauma
- Endolymphatic hydrops
This list is far from exhaustive.
There are no pharmaceutical treatments for this condition. A sufferer is likely to be treated with either Cognitive Behavioural Therapy or Retraining Therapy (similar to that employed for treating tinnitus), using pink noise.
A modern example of psychoacoustics in action is the Mosquito, a technical innovation designed to discourage teenagers from gathering in public spaces (e.g. outside shops, in public parks, outside business premises). In a nutshell, the Mosquito is a speaker that generate an annoying whine (hence the name).
Because the ability to hear higher frequencies declines as we get older, the Mosquito works by generating noise at frequencies to which under 18s are particularly sensitive, around 17.4 kHz.
Although a proven and effective method of dispersing crowds of youths, the Mosquito is a controversial innovation. In 2008, the National Autistic Association expressed concern that the device might adversely affect people with autism. The German Federal Institute for Occupational Safety and Health said the noises coming from the Mosquito could result in dizziness, headache, nausea, as well as effecting a ‘target’s’ equilibrium, increasing their risk of accident. And in the UK, the civil liberties and human rights organisation, Liberty, has expressed concern that the device may in fact violate sections 8 and 14 of the European Convention on Human Rights, as well as the United Kingdom's Human Rights Act 1998.
A final word
This is, of course, a far from comprehensive article on the fascinating subject of psychoacoustics. In fact, it only scrapes the very tip of the iceberg on the subject. But if this has given you a taste for the topic, there are a number of books available at amazon: click here.