Bertram Scharf Laboratoire do Mécanique et d'Acoustique, CNRS, Marseille, and Auditory Perception Laboratory, Northeastern University
In this chapter I document the immense advantage of ratio scaling, especially magnitude estimation, in the measurement of loudness adaptation. By loudness adaptation I mean ( Scharf, 1983): "a decrease in the loudness of a steady sound over time" (p. 1). The advantage of magnitude estimation applies to other types of sensory adaptation but is especially important for loudness, where strong interaural interactions have misled many a researcher. A classical approach to measuring loudness adaptation has been via interaural loudness matches. Turn on a sound and then judge its loudness in comparison to that of some other occasional sound. Presenting the comparison sound to the contralateral ear avoids any interruption of the continuous sound. Such procedures, referred to as simultaneous dichotic loudness balance, have revealed as much as 40 dB of "loudness adaptation" after a few minutes of exposure (e.g., Hood, 1950; Kärjä, 1968).
The problem is that the supposedly neutral comparison sound is not a disinterested measuring stick but interacts with events in the other, test ear thereby provoking the observed loudness decline. Early on, Bocca and Pestalozza ( 1959), Elliot and Fraser ( 1970), and Ward ( 1973) pointed out this possibility. One way to circumvent the problem of interaural interaction is to turn off the test sound just before turning on a comparison sound in the other ear. Using this method, referred to as delayed dichotic loudness balance, several early investigators (e.g., Békésy 1929) reported sizable adaptation, but a number of contemporary papers (e.g., Harbert, Weiss, & Wilpizeski, 1968) report no adaptation. Aside from the discrep-