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...
Recently, electromyographic (EMG) signals of auricular muscles have been shown to be an indicator of spatial auditory attention in humans, based on a vestigial pinna-orienting system. Because spatial auditory attention in a competing speaker task is closely related to the more generalized concept of attentional effort in listening, the current study investigated the possibility that the EMG activity of auricular muscles could also reflect correlates of effortful listening in general. Twenty subjects were recruited. EMG signals from the left and right superior and posterior auricular muscles (SAM, PAM) were recorded while subjects attended a target podcast in a competing speaker paradigm. Three different levels of listening effort, low, medium, and high, were generated by varying the number and pitch of distractor streams, as well as the signal-to-noise ratio. All audio streams were either presented from a loudspeaker placed in front of the participants (0 deg), or in the back (180 deg). Averaged PAM activity was not affected by different levels of listening effort, but was significantly larger when stimuli were presented from the back, as opposed to the front. Averaged SAM activity, however, was significantly larger in the high listening effort condition, compared to low and medium, but was not affected by stimulus direction. We hypothesize that the increased SAM activity is a response of the vestigial pinna-orienting system to effortful stream segregation task.
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