When I am in an essentially silent place I can hear a very faint droning or hissing. Can you tell me what this 鈥渟ound of silence鈥� white noise is and why I hear it?
鈥� The faint droning or hissing could occur for several reasons. It could be a result of a mild form of tinnitus, or ringing in the ears, which is experienced by about one in five people. Tinnitus can be caused by a wide range of factors including medication, reaction to certain foods or exposure to loud noise. The sounds could also be caused by spontaneous neural firing which occurs in the absence of sound stimulation in most mammals as a result of the brain 鈥渓istening out鈥�.
鈥淚f the intensity of a stimulus is slowly increased from a very low value, there is no well-defined point at which human ears are suddenly able to detect it鈥�
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However, another less well-known reason for hearing a hissing or droning sound is described by signal detection theory. If the intensity of a stimulus is slowly increased from a very low value, there is no well-defined point at which human ears are suddenly able to detect it. Instead there are a range of intensities over which someone will report a signal at some times and not at others. This was outlined by Brian Moore in An Introduction to the Psychology of Hearing (Academic Press, 1989). So the hissing could be caused by the gradual detection of a very low intensity noise.
Ian Smith, London, UK
鈥� The hissing is possibly tinnitus. I suffer from it myself, in the form of a high-pitched mush of no particular frequency. Mine is very faint, and can only be heard in very quiet situations.
The accompanying drone is less likely to be in the ears. Low-frequency sounds can travel through solid structures such as buildings. It may be worthwhile checking the frequency of the drone, which is probably mains frequency or a harmonic. If it is, sources in the home could include the refrigerator, the central heating system or a fluorescent light.
Tim Gossling, Cambridge, UK
鈥� It sounds to me like a description of mild tinnitus. I suffered profound ear damage at the age of seven, but it was not until I was 34 years old that I found out that not everyone has whistling, droning, clicking, whirring or buzzing noises as a soundtrack to everyday life. I consider myself lucky because my version is generally monotonic and quite high pitched, and so fairly easy to ignore in everyday circumstances. However, when I have a head cold or ear infection I become much more aware of the sounds 鈥� they seem to drop in pitch and intrude much more, blocking out some external sounds and reducing my hearing still further.
Some unfortunate individuals describe their tinnitus as a hard, mechanical chattering which intrudes into every aspect of their waking lives. Have your ears tested and use ear-defenders or hearing protection whenever necessary.
Norman McCanch, Canterbury, Kent, UK
Most people seem to notice a mild hissing or hum in otherwise quiet conditions. However, if it is loud and persistent or increasing in intensity, you should visit a doctor to rule out any underlying problem 鈥� Ed