The spectrally dependent monotic component in the decreasing-loudness aftereffect: Implications for dynamic auditory localization

Listeners exposed to a tone increasing in intensity report an aftereffect o f decreasing loudness in a steady tone heard afterward. In the present stud y, the spectral dependence of the monotic decreasing-loudness aftereffect ( adapting and testing 1 ear) was compared with (a) the spectral dependence o f the interotic decreasing-loudness aftereffect (adapting 1 ear and testing the other ear) and (b) a non-adaptation control condition. The purpose was to test the hypothesis that the decreasing-loudness aftereffect may concer n the sensory processing associated with dynamic localization. The hypothes is is based on two premises: (a) dynamic localization requires monaural sen sory processing, and (b) sensory processing is reflected in spectral select ivity. Hence, the hypothesis would be supported if the monotic aftereffect were more spectrally dependent and stronger than the interotic aftereffect; A. H. Reinhardt-Rutland (1998) showed that the hypothesis is supported wit h regard to the related increasing-loudness aftereffect. Two listeners were exposed to a 1-kHz adapting stimulus. From responses of "growing softer" o r "growing louder" to test stimuli changing in intensity, nulls were calcul ated; test carrier frequencies ranged from 0.5 kHz to 2 kHz. Confirming the hypothesis, the monotic aftereffect peaked at around the 1-kHz test carrie r frequency. In contrast, the interotic aftereffect showed little evidence of spectrally dependent peaking. Except when test and adaptation carrier fr equencies differed markedly, the interotic aftereffect was smaller than the monotic aftereffect.