The growing-louder effect in short diotic stimuli.

Previous evidence from short monotic stimuli shows that a steady stimulus is perceived as growing louder; to be perceived as steady, the intensity of the stimulus must decrease. In the present study, 10 subjects heard a sequence of diotic tonal stimuli. Each stimulus lasted 1.5 sec. and increased, decreased, or remained steady in intensity; initial intensity was 40 dB SPL and carrier frequency was 1 kHz. Subjects made forced binary responses of "growing louder" or "growing softer" to each stimulus. Confirming the evidence from monotic stimuli, the mean value of changing intensity eliciting equal numbers of both responses was negative. Possible explanations for this growing-louder effect reside in (a) the percussive nature of many natural sounds and (b) selective responding to approaching sound-sources.