PROJECT SUMMARY/ABSTRACT The relatively slow variations in amplitude across time (amplitude modulation or AM) inherent to many behaviorally relevant sounds are of fundamental importance to auditory perception and communication. This is true for listeners with normal hearing, listeners with hearing loss, and, in particular, for listeners with cochlear implants, for whom AM cues are the dominant source of auditory information in some settings. The broad goal of the work proposed here is to better understand how listener uncertainty and expectation affect AM processing and perception in dynamic, multisource listening environments. The work is structured under two specific aims. In Aim 1, a series of experiments using novel and innovative psychophysical techniques, which build upon and extend those used previously to characterize the effects of listener uncertainty and expectation in the context of auditory informational masking, are proposed in order to characterize how listener uncertainty and expectation affect the processing of AM. In Aim 2, further experiments using similar techniques are proposed to characterize individual differences in this area. While the focus in both cases is on listeners with normal hearing, the proposed experiments nevertheless may yield clinically relevant results. For example, the dynamic range compression algorithms common to many current-generation digital hearing aids can introduce rapid, unpredictable changes to the AM content of a scene, thereby inducing uncertainty in the listener. A better understanding of how listener uncertainty and expectation affect AM processing and perception in listeners with normal hearing, then, may yield insights into the factors that affect aided multisource listening. Moreover, given the importance of AM cues to listeners with cochlear implants, a better understanding of individual differences in this area may help to explain the large individual differences in outcome measures and communication successes exhibited by this listener group. Thus, the work proposed here is directly in line with NIDCD's mission and strategic plan of understanding normal auditory function so as to improve diagnosis, treatment, and communication outcomes for listeners with auditory communication disorders. The PI of this fellowship application is an advanced predoctoral student at Boston University, where the work will be conducted. A sponsorship team comprising world renowned experts in the field of auditory psychophysics has been assembled that will provide training to the applicant in the core areas of psychophysical theory, experimental techniques, and data analysis methodology. This training, together with supplemental coursework, attendance at various workshops, regular presentations at conferences, and an assortment of professional development activities, will prepare the applicant for the next stage of a productive career as an independent researcher in the field of auditory perception and communic...