In praise of adventitious sounds.

Study of the characteristics, neural processing, and behavioral effects of communication sounds are an important focus of hearing research. The goal of this paper is to bring attention to another, rather neglected class of sounds that are omnipresent and that are arguably at least equally important for the daily survival of many species and have been in the evolution of the mammalian auditory system. All terrestrial mammals produce adventitious sounds when they locomote. The handful of studies that examined the characteristics of such sounds suggests that high-frequency transients are an important component. Acoustic propagation of such sounds is limited in distance, particularly for sources and receivers on a vegetated ground plane. It follows that the presence of such sounds is an indication of a nearby animal, and that detection and localization of high-frequency transients is vital for both prey and predator. It is suggested that consideration of adventitious sounds is important in grasping the importance of auditory morphological and physiological features. As an illustration, a hypothesis on the relationship of one binaural brainstem circuit to adventitious sounds is briefly discussed.