Summary: The auditory system tracks the speed and location of moving sounds.
The brain’s auditory system tracks the speed and location of moving sounds in the same way the visual system tracks moving objects.
The study recently published in eNeuro lays the groundwork for more detailed research on how humans hear in dynamic environments.
People who use hearing aids have trouble discriminating sounds in busy environments. Understanding if and how the auditory system tracks moving sounds is vital to improving hearing aid technology.
Prior research utilizing eye movements to gauge whether the brain is following the trajectory of a moving sound indicates it cannot. A new study from García-Uceda Calvo et al. instead used head movements, a more accurate measure of sound tracking.
The team analyzed head movements of hearing participants as they tracked randomly moving sounds in a dark room. Their analysis revealed humans follow moving sounds, with great accuracy.
The auditory system actively tracks the velocity of a sound, just like the visual system, rather than changes in position.
The participants improved their sound tracking ability over the course of the experiment, a sign the auditory system was picking up on hidden patterns in the sound trajectories and making predictions.
These results indicate the brain possess cells and circuits dedicated to tracking the velocity of sounds.
About this auditory neuroscience research news
Source: SfN Contact: Calli McMurray – SfN Image: The image is credited to García-Uceda Calvo et al., eNeuro 2021
Adaptive Response Behavior in the Pursuit of Unpredictably Moving Sounds
Although moving sound-sources abound in natural auditory scenes, it is not clear how the human brain processes auditory motion. Previous studies have indicated that, although ocular localization responses to stationary sounds are quite accurate, ocular smooth pursuit of moving sounds is very poor.
We here demonstrate that human subjects faithfully track a sound’s unpredictable movements in the horizontal plane with smooth-pursuit responses of the head.
Our analysis revealed that the stimulus–response relation was well described by an under-damped passive, second-order low-pass filter in series with an idiosyncratic, fixed, pure delay. The model contained only two free parameters: the system’s damping coefficient, and its central (resonance) frequency. We found that the latter remained constant at about 0.6 Hz throughout the experiment for all subjects.
Interestingly, the damping coefficient systematically increased with trial number, suggesting the presence of an adaptive mechanism in the auditory pursuit system. This mechanism functions even for unpredictable sound-motion trajectories endowed with fixed, but covert, frequency characteristics in open-loop tracking conditions.
We conjecture that the auditory pursuit system optimizes a trade-off between response speed and effort. Taken together, our data support the existence of a pursuit system for auditory head-tracking, which would suggest the presence of a neural representation of a spatial auditory fovea.
Inspired by the visual ocular smooth-pursuit system, several studies have used eye movements to track moving sounds, but obtained poor pursuit performance, which led to the idea that the auditory system lacks sensitivity to sound velocity. We here demonstrate accurate head-pursuit of sounds, moving along unpredictable trajectories in the horizontal plane.
Interestingly, the auditory pursuit responses adapted to the covert movement spectrum of the stimulus ensemble, from which we infer that the system may optimize a trade-off between movement speed and effort.
Our results support the existence of an auditory pursuit system, and we discuss its implications for the neural mechanisms that represent and track moving sounds.