Edited by Terrence J. Sejnowski, Salk Institute for Biological Studies, La Jolla, CA, and approved May 12, 2017 (received for review February 16, 2017)
Humans and other animals continuously monitor sensory information to inform the selection of motor commands for adaptive behaviors. Acoustic communication, for example, utilizes auditory feedback to fine-tune vocal production parameters. Because most animal species produce vocalizations that last several hundred milliseconds, it is difficult to dissect the temporal dynamics of audio-vocal feedback control. Here we took advantage of the brief echolocation signals of bats and mapped out the time course of vocal adjustments to background noise on a millisecond time scale. The high temporal resolution data provided the foundation for the model of audio-vocal volume control. We discovered that temporal summation, a shared auditory process across the animal kingdom, lies at the core of adaptive vocal volume control.
Sensing is fundamental to the control of movement: From grasping objects to speech production, sensing guides action. So far, most of our knowledge about sensorimotor integration comes from visually guided reaching and oculomotor integration, in which the time course and trajectories of movements can be measured at a high temporal resolution. By contrast, production of vocalizations by humans and animals involves complex and variable actions, and each syllable often lasts a few hundreds of milliseconds, making it difficult to infer underlying neural processes. Here, we measured and modeled the transfer of sensory information into motor commands for vocal amplitude control in response to background noise, also known as the Lombard effect. We exploited the brief vocalizations of echolocating bats to trace the time course of the Lombard effect on a millisecond time scale. Empirical studies revealed that the Lombard effect features a response latency of a mere 30 ms and provided the foundation for the quantitative audiomotor model of the Lombard effect. We show that the Lombard effect operates by continuously integrating the sound pressure level of background noise through temporal summation to guide the extremely rapid vocal-motor adjustments. These findings can now be extended to models and measures of audiomotor integration in other animals, including humans.
Author contributions: J.L. and N.B.K. designed research; J.L. and N.B.K. performed research; J.L. analyzed data; and J.L. and C.F.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702671114/-/DCSupplemental.
