A comparison of comodulation masking release and profile analysis

Abstract

Large reductions in signal thresholds may be observed under stimulus conditions in which there is common information in a number of auditory channels or critical bands. In comodulation masking release (CMR) tasks, a reduction in the threshold of a signal in a narrow‐band noise occurs when a flanking or cue band of noise is also present, provided that the flanking band has an amplitude envelope which is correlated with that of the masker band. This reduction in threshold occurs in dichotic conditions, where the flanking band is presented in the opposite ear to the signal‐plus‐masker. In profile analysis (PA), the overall level is randomized from one stimulus to the next. The threshold for detecting an increment in level of a single component is reduced when flanking components equal in amplitude to the pedestal are added. In general, this effect has not been found when the flanking components are presented dichotically. The present work examines the extent of the similarity, and divergence, between CMR and PA. For the PA conditions, a five‐component sinusoidal complex was used; its level was varied randomly over a 40‐dB range. For the CMR conditions, each of the five components was 100% sinusoidally amplitude modulated at a 10‐Hz rate. Two intermediate conditions of PA without the level variation, and CMR with the level variation, were also run. All four conditions were run monaurally and dichotically. A reference condition in which only one masking component was present was also used. For PA conditions when the stimulus level was randomized, thresholds in the monaural and dichotic conditions were 16 and 11 dB lower than in the reference condition, respectively. By contrast, for the CMR conditions, whether the stimulus level was randomized or not, thresholds in the reference, monaural and dichotic conditions differed by little more than 3 dB; i.e., no CMR was observed. Further experiments are now in progress to determine why a CMR was not observed in these conditions.