Vestigial auriculomotor activity indicates the direction of auditory attention in humans

Abstract

<jats:p>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.</jats:p>

Fast EEG-Based Decoding Of The Directional Focus Of Auditory Attention Using Common Spatial Patterns

“…10. (e.g., lateral movements) and EMG activity (especially subtle directive ear movements [37]). However, there are several indications that the CSP filters do not exploit these effects and indeed focus mainly on neural activity.…”

“…As ear movements spectrally (β-and γ-band) overlap with the information used by the CSPs, it is more difficult to exclude the exploitation of subtle ear movements [37]. There are, however, two counterindications.…”

Muscles in and around the ear as the source of “physiological noise” during auditory selective attention: A review and novel synthesis

“…The postauricular muscle (PAM) is noteworthy in having an extremely large EMG signal (up to 250 µV p‐p) yet is a vestigial muscle that has been called a cognitive or neural “fossil” (Hackley, 2015; Strauss et al., 2020). As noted, it sits behind the ear, and is brought into play when the ear is wiggled or a click or tone‐burst enters the auditory system (O'Beirne & Patuzzi, 1999).…”

“…The muscle is situated right behind the pinna, and in animals with large pinnas it has an important role in moving the external ear in the direction of a sound source. In humans, of course, only a few talented individuals can move their ears (Strauss et al., 2020). Notwithstanding, the PAM reflex is strong in some 96% of individuals, although its amplitude can vary greatly (by a factor of 10 or more) depending on tension (Hackley, 2015; Patuzzi & O'Beirne, 1999).…”

“…This paper also draws attention to recent work that has implicated eye movements resulting from co-activation of the ocular muscles and the ear muscles (Gruters et al, 2017;Strauss et al, 2020), and these additional factors are also relevant to the whole issue of which facial muscles might be contributing responses to experimental stimuli. The conclusion reached is that, in the complex field of selective attention, experiments involve underlying factors which have not so far been well appreciated.…”