Influence of the preceding item in measurements of the noise-masked thresh-old by a modified constant method.

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Abstract
A tone lasting 3 sec. was presented to the ear at 5-sec. intervals in a constant background of thermal noise. The intensity of the tone was changed by random discrete steps from one presentation to the next. The percentage of tones detected at each intensity was observed to vary with the intensity of the preceding tone. Within one db of threshold (the intensity at which 50% of the tones presented are detected), the number of equally intense signals detected varies by approx. 25% as a function of the preceding signal. A relatively intense preceding signal reduces the percentage detected, a moderately intense preceding signal increases it, and a preceding signal at the same intensity slightly reduces it. For mitigating the influence of the preceding item a sequence of a chosen set of signal intensities is given in which each precedes all of the others and itself very nearly the same number of times.
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