Vestigial Auriculomotor Activity Indicates the Direction of Auditory Attention in Humans

Abstract

AbstractIt is commonly assumed that, unlike dogs and cats, we humans do not make ear movements when focusing our attention reflexively toward novel sounds or voluntarily toward those that are goal–relevant. In fact, it has been suggested that we do have a pinna–orienting system. Although this system became vestigial about 25 million years ago, it still exists as a “neural fossil” within the brain. Consistent with this hypothesis, we demonstrate for the first time that the direction of auditory attention is reflected in the sustained electrical activity of muscles within the vestigial auriculomotor system.Surface electromyograms (EMGs) were taken from muscles that either move the pinna or alter its shape. To assess reflexive, stimulus-driven attention we presented novel sounds from speakers at four different lateral locations while the participants silently read a boring text in front of them. To test voluntary, goal-directed attention we instructed participants to listen to a short story coming from one of these speakers, while ignoring a competing story from the corresponding speaker on the opposite side.In both experiments, EMG recordings showed larger activity at the ear on the side of the attended stimulus, but with slightly different patterns. Upward movement (perking) differed according to the lateral focus of attention only during voluntary orienting; rearward folding of the pinna’s upper-lateral edge exhibited such differences only during reflexive orienting. The existence of a pinna-orienting system in humans, one that is experimentally accessible, offers opportunities for basic as well as applied science. It could lead to a better understanding of the evolution of auditory attention and support the near real–time decoding of auditory attention in technical applications, for example, for attentionally controlled hearing aids that preferentially amplify sounds the user is attempting to listen to.