The influence of noise on emotional states.

NOISE exists in many different forms [1], but in noise of human origin; in speech and in inarticulate cries, it can be defined as sound whose frequency lies above and below the frequency band 200 Hz-8kHz wherein lies most of the intelligibility of lettered speech [2]. This high frequency sound, from 8 kHz to 40 kHz is also found in the physical environment. Here, it is associated with sounds of an arresting nature. Examples are, an alarm bell, a baby's rattle, a toy xylophone, a child screaming, an adult force breathing, and a child coughing. In Fig. 1, they are presented in the form of spectrograms, where the ordinate is the amplitude, recorded by a third octave band analyser at 10, 12.5, 16, 20, 25, 31.5, and 40 kHz. It is interesting to note that a weak source, such as the xylophone seems to attract the listener whereas a strong one, with similar spectrum of frequencies, such as the child screaming seems to repel. When the sound maintains its amplitude at the higher frequencies, and is, in itself, a strong source, then it appears to be a universally disturbing sound. This can be seen in the spectrum of the alarm bell. Similar spectrograms of weak sources, such as the sounds of an apple being eaten, the scratching of the skin, the snapping of the fingers, and the rustling of paper, are associated with sounds that only disturb the listener, and may, in fact, please the originator. (Fig. 2.) High frequency sound can also disturb, by distracting the attention of the listener from a low frequency source. This effect can be noticed when an individual coughs at a lecture, or someone unwraps a box of chocolates, in the quiet of a theatre. In any complex sound, as in the sudden screaming of a child, the low frequency elements are uniformly spread in a circle round the source of the sound, but as the frequency of the sound waves rises, the higher frequency elements are radiated more and more directionally in a beam. Therefore, if a child is screaming at another child, between the originator and the recipient, there exists a difference in the degree of exposure to the high frequency content of the scream. It can be noted from experience, that a child screaming in anger at another does in fact turn his head, and direct the sound waves straight at the recipient. In so doing, the originator minimises his own exposure to the high frequency sound waves, and maximises the exposure of the recipient. It seems not unreasonable to assume that the emotional shock to the recipient results from the unequal distribution of the high frequency sound. In order to discover what significance could be attached to the presence of high frequency sound in human conversation, an experiment was performed in which this element of the voice pattern was measured in two groups of subjects. These consisted of asthmatic and control families. An asthmatic family was defined as one containing one or more members, who at one time or another, had exhibited attacks of asthma. The control families had no such members. Each of the subjects was asked to recite the 26 letters of the English alphabet, and the amplitude of the sound, was measured