The Discrimination Limen for Loudness under Varying Rates of Intensity Change

Abstract

Two studies have been conducted on the influence of the rate of auditory intensity change upon a subject's ability to discriminate that change. In experiment I the stimulus intensity changed gradually through time. Complete psychophysical functions were obtained for four subjects at five rates of change between 2 and 150 db/min. To control for possible differential auditory fatigue effects, a stable level of fatigue was maintained throughout the trials. The slowest rate of change was the only one which produced results significantly different from the other rates and this was so for only two of the four subjects. In experiment II a warbling type of intensity variation was used with four warble rates between 0.3 and 3.0 beats/sec. The rate of change of the warble amplitude was adjusted for each warble rate to serve as a compensation for the fewer number of warble cycles presented in a given observation time with the slower warble rates. This control has apparently not been used before in two previous similar studies whose results indicated a very definite decrement in discrimination as the warble rate decreased. The results from this experiment showed no significant effects on the DL from varying the warble rate. The results will be discussed in terms of individual differences and changing discriminative criteria as they relate to temporal factors.