Psychophysical Studies of Auditory Masking in Marine Mammals: Key Concepts and New Directions

Abstract

In recent years, growing awareness of the potentially harmful effects of human-generated noise has led to concern over whether and how increasing ocean noise levels may adversely affect marine mammals by interfering with their detection of biologically important signals. The consequences of adding noise to an animal’s environment may be studied, in part, by identifying and understanding the ways in which noise alters normal or baseline hearing capabilities. The process of auditory masking occurs when the perception of a given signal is negatively influenced by the presence of another sound. Masking effects may be manifested through spectral or temporal interference from noise that decreases the audibility of the signal relative to conditions when the masking noise is not present. In addition to auditory-masking effects, it should be noted that other auditory effects as well as nonauditory behavioral, physiological, or anatomical changes may also occur as a result of noise exposure. Furthermore, marine mammals are not the only aquatic animals that may be vulnerable to these effects. However, the scope of this paper is limited to consideration of the masking effects of noise on the auditory perception of marine mammals. The specific aims are to 1) briefly review the key concepts and methods drawn from a psychophysical approach to the study of auditory masking, 2) examine how masking studies have been applied thus far to improve understanding of noise effects on marine mammals, and 3) consider how future laboratory studies with marine mammals may incorporate progressively more complex and realistic listening scenarios into psychophysical testing programs.