Examining the influence of forward, backward, and simultaneous notched noise on the mid-level hump in intensity discrimination

Abstract

Psychoacoustical intensity discrimination limens (IDLs) for high frequency, short duration pedestals are poorer at mid levels than at lower and higher levels. It has been theorized that this so-called midlevel hump (MLH) may reflect mid-level cochlear compression, whereas the improvement at higher levels may be due to spread of excitation cues. To characterize intensity discrimination within a single frequency channel, researchers (e.g., Plack, 1998) have used simultaneous notched noise (NN) to limit cues from the spread of excitation to other channels. However, additional effects of the NN on the pedestal remain a matter of debate. The NN may provide a reference against which intensity judgments are made. Additionally, the NN may produce excitatory masking in the pedestal frequency channel, suppress the pedestal, and evoke cochlear gain reduction via the medial olivocochlear reflex. These latter two mechanisms change the basilar membrane compression slope, but operate over different time courses. In the present study, we examine the MLH with different durations of forward, backward, and simultaneous NN and pure tone maskers to isolate these potential mechanisms. Results will be interpreted using a computational model of the auditory system. [Research support provided by grants from NIH (NIDCD): R01-DC008327 and the Purdue Research Foundation.]