Primary speech frequencies: Adaptation inside versus outside—Inhibition or excitation?

Abstract

Previously, loudness adaptation from the ipsilateral comparison paradigm (ICP) and the simple adaptation (SA) procedure were compared at primary speech‐ related frequencies (250 to 4000 Hz), with only the ICP showing significant loudness decline/adaptation [Tannen et al., J. Gen Psychol. 128, 385–399 (2001)]. Eighty naive undergraduates participated in any one of three subsequent studies of ICP versus SA adaptation. In agreement with Tannen et al., only the ICP showed significant loudness decline/adaptation from 250 to 6000 Hz. However, at 8000 Hz both the ICP and SA show significant adaptation, and correlate significantly. However, despite the lack of correlation between individual scores under 8000 Hz, a further analysis of group mean values from 250 to 8000 Hz showed a significant correlation (r=0.97, p<0.001). Perhaps the SA procedure shows a lack of adaptation at speech frequencies because the method is insensitive. Alternatively, it may be considered that a ‘‘stable platform’’ [i.e., no adaptation for constant stimuli] favors the perception of the constantly varying speech signals. Support for the ‘‘stable platform’’ versus the ‘‘insensitivity’’ hypothesis will be discussed.