Loudness adaptation: real or illusory.

There is general agreement that, except at low sensation levels, the loudness of a continuous pure tone does not appear to change with time. By contrast, using a simultaneous dichotic loudness balancing procedure (SDLB) a substantial fall in loudness can be revealed. As a result it has been held that the latter does not represent a loudness loss in real terms but is a manifestation of some form of central binaural interaction possibly involving localization mechanisms. In two studies reported here, one involving a loudness scaling procedure using as a standard a reference tone of 65 dB (HL) and the other a loudness doubling procedure, a loudness loss has been clearly demonstrated following sustained stimulation with a continuous 60-dB (HL), 1000-Hz tone applied monaurally. The progression of the loudness loss with time follows a similar course to that found with the SDLB procedure. In consequence it is concluded that both represent a loudness loss in real terms and that inability to detect a change in loudness over time of a continuous tone results from the absence of any reference standard by which it can be judged.