The Lombard effect and other noise‐induced vocal modifications: insight from mammalian communication systems

Abstract

Humans and non-human mammals exhibit fundamentally similar vocal responses to increased noise, including increases in vocalization amplitude (the Lombard effect) and changes to spectral and temporal properties of vocalizations. Different research focuses have resulted in significant discrepancies in study methodologies and hypotheses among fields, leading to particular knowledge gaps and techniques specific to each field. This review compares and contrasts noise-induced vocal modifications observed from human and non-human mammals with reference to experimental design and the history of each field. Topics include the effects of communication motivation and subject-specific characteristics on the acoustic parameters of vocalizations, examination of evidence for a proposed biomechanical linkage between the Lombard effect and other spectral and temporal modifications, and effects of noise on self-communication signals (echolocation). Standardized terminology, cross-taxa tests of hypotheses, and open areas for future research in each field are recommended. Findings indicate that more research is needed to evaluate linkages among vocal modifications, context dependencies, and the finer details of the Lombard effect during natural communication. Studies of non-human mammals could benefit from applying the tightly controlled experimental designs developed in human research, while studies of human speech in noise should be expanded to include natural communicative contexts. The effects of experimental design and behavioural context on vocalizations should not be neglected as they may impact the magnitude and type of noise-induced vocal modifications.

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…Thus a behavioural adaptation whereby dolphins attempt to increase their call amplitude above masking noise to minimize any reduction in whistle communication range might also explain the frequency shift we observed. Research devoted to understanding a possible connection between the Lombard effect and other noise-induced vocal modifications, including frequency shifts, has received minimal attention in the nonhuman field of communication research (Hotchkin & Parks, 2013). As we could not measure whistle source levels, it was not possible for us to determine whether the shifts in frequency we observed were accompanied by amplitude modifications.…”

“…Previous studies investigating the Lombard effect in cetaceans did not investigate concurrent changes in signal frequency (Holt et al, 2009;Scheifele et al, 2005) or failed to demonstrate a frequency shift associated with increased amplitude (Holt et al, 2015;Parks et al, 2011). However, as this research area is in its infancy, a possible coupling between the Lombard effect and other noise-induced vocal modifications in cetaceans warrants further investigation (Hotchkin & Parks, 2013).…”

“…The ultimate aim of most noise-induced vocal modification is to maintain the signal-to-noise ratio of calls during increased ambient noise (Hotchkin & Parks, 2013). In species that display vocal plasticity, such as birds, bats and cetaceans, shifts in call frequency can help achieve this and geographical variation in these call parameters has been linked to natural variation in ambient noise levels from biotic and abiotic factors (Brumm & Slabbekoorn, 2005;Foote & Nystuen, 2008;Hage, Jiang, Berquist, Feng, & Metzner, 2013;Mossbridge, Shedd, & Thomas, 1999).…”

“…Where explicitly studied, the Lombard effect has been demonstrated in all nonhuman mammalian species (Hotchkin & Parks, 2013), including several cetacean species (Holt et al, 2009;Parks et al, 2011;Scheifele et al, 2005). In several bird and mammal species, the Lombard effect is associated with a range of other changes in vocal output, including a rise in fundamental frequency (Dabelsteen, 1984;Hotchkin, Parks, & Weiss, 2015;Nelson, 2000;Nemeth et al, 2013;Ritschard & Brumm, 2011;Tressler & Smotherman, 2009).…”

Sensorimotor integration on a rapid time scale

“…Evidence of the Lombard effect comes from studies of mammals (including humans), birds, frogs, and fish (12)(13)(14)(15)(16). Despite over a century of research, the brain mechanisms of the Lombard effect remain elusive.…”