Apparent fluctuations of a sensory threshold

An account is given of a method for the nearly continuous recording of sensory thresholds and other psycho-physical variables. Its application to the difference-threshold for sound-intensity is described. It is found that this threshold, so recorded, shows irregular fluctuations in time, excursions of up to 100 per cent, being commonly present. There is no prima facie indication of any regular periodicity in the fluctuations. No evidence was found of any general trend in amount of fluctuation throughout a half-hour period of observation. Nor, except in one subject, was there any tendency for the amount of fluctuation to increase or decrease over a series of six half-hour periods of observation. There are marked, and fairly consistent, differences between individual subjects as regards the amount and pattern of fluctuation. The possible locus and causes of these effects are briefly considered.