The Lombard Effect: From Acoustics to Neural Mechanisms

• Published in: Trends in neurosciences (Regular ed.) Vol. 41; no. 12; pp. 938 - 949
• Main Authors: Luo, Jinhong, Hage, Steffen R., Moss, Cynthia F.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2018
• Subjects: acoustic communication; ambient noise; Animals; audiovocal integration; Brain - physiology; cognitive networks; Humans; Noise; Phylogeny; subcortical circuits; Verbal Behavior - physiology; vocal motor control; Vocalization, Animal - physiology; subcortical circuits; acoustic communication; cognitive networks; vocal motor control; audiovocal integration; ambient noise
• ISSN: 0166-2236; 1878-108X; 1878-108X
• DOI: 10.1016/j.tins.2018.07.011

Understanding the neural underpinnings of vocal–motor control in humans and other animals remains a major challenge in neurobiology. The Lombard effect – a rise in call amplitude in response to background noise – has been demonstrated in a wide range of vertebrates. Here, we review both behavioral and neurophysiological data and propose that the Lombard effect is driven by a subcortical neural network, which can be modulated by cortical processes. The proposed framework offers mechanistic explanations for two fundamental features of the Lombard effect: its widespread taxonomic distribution across the vertebrate phylogenetic tree and the widely observed variations in compensation magnitude. We highlight the Lombard effect as a model behavioral paradigm for unraveling some of the neural underpinnings of audiovocal integration. The Lombard effect is a phylogenetically ancient audiovocal phenomenon that may have emerged ∼450 million years ago. The Lombard effect is elicited by a subcortical network that processes acoustic features of stimuli, such as amplitude, frequency, and duration. The Lombard effect is better explained by the SNR between a subject’s vocalization and ambient noise, than by the amplitude of ambient noise per se. The physiological SNR of the auditory system is influenced by various parameters such as amplitude, call frequency, and duration, and Lombard effect for a given vocalization is determined by these parameters collectively. Cortical networks can play a modulatory role in the Lombard effect, and may differentially influence the Lombard effect across groups of animals that differ with respect to neuroanatomical structure and organization. The Lombard effect serves as a valuable behavioral paradigm to unravel the neural underpinnings of audiovocal integration, which is essential to many other aspects of vocal control.