The Physiology of Concentration

Author: N.H. Crowhurst

Concentration is aided by two things: your sense of direction (which helps you to concentrate on sound coming from where your friend is standing) and the individual characteristics of his voice (his "voice personality") which helps you to separate what he is saying from what people with different voice personalities are saying. How is this discrimination achieved, when all we can really tell apart (in audio terms) is the frequency content and the intensity of individual frequencies.

It is all possible due to the form that individual hearing perception takes in its transmission from the individual ears to the brain. Each ear has a number of resonators in the cochlea that are sensitive to individual frequencies, using from 20 to 29,000 to cover the entire audio frequency range. Each of these receptors, however, does not transmit its individual frequency to the brain. What it does transmit is a series of nerve pulses.

The first pulse to be transmitted to the brain is sent when that particular frequency is first detected by the ear. Thereafter, a sequence of pulses is sent along the same nerve fiber, dependent upon the intensity of that frequency at the instant. The louder the sound component of the particular frequency, the more frequently this nerve carries pulses to the brain.

The section of the brain devoted to the analysis of sounds heard "recognizes" a complicated pulse pattern by comparison with patterns already familiar. There are a number of characteristics by which the patterns can vary, enabling deliberate "differential listening." The most important part of any group of patterns is the first set of pulses along any particular grouping of nerve fibers. This is the transient effect of the sound heard. The following grouping indicates the way the sound varies in intensity or tone quality after it first starts.

The auditory nerve conveys to the brain a pulse code pattern corresponding with all the sounds being heard all the time. The code can be decoded in a variety of ways because of its enormous complexity and the vast resources of the brain cells that interpret sound. Sounds can be grouped, for example, according to the particular pattern of fundamental and overtones characteristic of a violin. Thus, when listening to orchestral music, the sound of the violin can be distinguished from all the other musical sounds going on at the same time. Similarly, one person's voice can be singled out from the voices of many other people by noticing the pattern peculiar to that person's voice personality. The automobile mechanic's ear becomes tuned to the sound patterns that come from each component in an automobile engine. As a result, he can distinguish a sound due to a knock in an end bearing as different from one due to loose valve tappets, among all the other engine noises.

Although the hearing faculty is extremely critical and can detect any particular sound with high precision, it is extremely tolerant; it can pay attention to what it wants to hear and ignore everything else.

The physiology of concentration