Unlike dogs and cats, people do not point their ears as they focus attention on novel, salient, or task-relevant stimuli. Our species may nevertheless have retained a vestigial pinna-orienting system that has persisted as a 'neural fossil’ within in the brain for about 25 million years. Consistent with this hypothesis, we demonstrate that the direction of auditory attention is reflected in 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.

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1It is commonly assumed that, unlike dogs and cats, we humans do not make 2 ear movements when focusing our attention reflexively toward novel sounds or 3 voluntarily toward those that are goal-relevant. In fact, it has been suggested 4 that we do have a pinna-orienting system. Although this system became ves-5 tigial about 25 million years ago, it still exists as a "neural fossil" within the 6 brain. Consistent with this hypothesis, we demonstrate for the first time that the 7 direction of auditory attention is reflected in the sustained electrical activity of 8 muscles within the vestigial auriculomotor system. 9 Surface electromyograms (EMGs) were taken from muscles that either move 10 the pinna or alter its shape. To assess reflexive, stimulus-driven attention we 11 presented novel sounds from speakers at four different lateral locations while the 12 participants silently read a boring text in front of them. To test voluntary, goal-13 directed attention we instructed participants to listen to a short story coming from 14 one of these speakers, while ignoring a competing story from the corresponding 15 speaker on the opposite side. 16 In both experiments, EMG recordings showed larger activity at the ear on the 17 side of the attended stimulus, but with slightly different patterns. Upward move-18 ment (perking) differed according to the lateral focus of attention only during 19 voluntary orienting; rearward folding of the pinna's upper-lateral edge exhibited 20 such differences only during reflexive orienting. The existence of a pinna-orienting 21 system in humans, one that is experimentally accessible, offers opportunities for 22 basic as well as applied science. It could lead to a better understanding of the 23 evolution of auditory attention and support the near real-time decoding of audi-24 tory attention in technical applications, for example, for attentionally controlled 25 hearing aids that preferentially amplify sounds the user is attempting to listen 26 to. 27 Introduction 28 A review of research (Hackley, 2015) on pinna-orienting in humans identified three rel-29 evant findings scattered across the preceding 100-or-so years. The first was Wilson's 30 (1908) (Wilson, 1908) oculo-auricular phenomenon, in which shifting the gaze hard to 31 one side elicits a 1 to 4 mm deflection of the lateral rim of both ears. The relevance to 32 spatial attention is uncertain, though, because the relation between the side with the 33 largest ear movement and that to which gaze is directed has been weak and inconsistent & Hillyard, 1987) of the bilateral postauricular muscle (PAM) reflex (onset latency = 37 10 ms) to acoustic onset transients. Increased amplitudes were observed when subjects 38 directed their attention to a stream of tones on the same side as the recorded muscle 39 while ignoring a competing, contralateral stream. Comparisons across left/right stim-40 ulus, attention, and PAM combinations localized modulation to the motor limb of the 41 reflex arc. This pattern could indicate that the muscle behind...