Researchers at Saarland University published a study in Frontiers in Neuroscience revealing that ancient auricular muscles in humans activate during challenging listening tasks, indicating that these vestigial muscles may still play a role in auditory processing. They found that when people focus on difficult listening tasks, the auricular muscles show electrical activity, similar to ear movements in other species that indicate attentiveness.
The study involved recruiting 20 participants without hearing problems and applying electrodes to their auricular muscles to measure electrical activity while they engaged in various listening tasks. The participants listened to an engaging audiobook for five minutes while simultaneously exposed to one or two distracting podcasts from the same speaker.
Each participant underwent 12 five-minute trials covering three different levels of difficulty: easy, medium, and hard. In the easy trials, the audiobook was much louder than the podcast, and the speaker's voice contrasted strongly with that of the audiobook. In the moderate and difficult trials, the audiobook was only slightly louder than the podcast, and the speakers' voices were similar, making it harder for participants to focus.
The researchers aimed to determine whether the activity of auricular muscles depends on the difficulty of the listening task, using electromyography to monitor electrical activity in muscle tissues. The study found that the more difficult the listening task, the more active the superior auricular muscles became. "These muscles, particularly the superior auricular muscle, show increased activity during challenging listening tasks," explained Andreas Schröer of Saarland University.
Participants were asked questions about the content of the audiobook to test their understanding and retention during the distraction. The researchers found that participants' scores declined as the difficulty of the task increased, and they reported having more trouble and losing track more often, matching their actual listening performance.
The superior auricular muscles reacted more strongly to the difficulty level of the task, especially when switching from medium to hard mode. In contrast, the posterior auricular muscles primarily reacted to changes in the direction of the sound. "The posterior auricular muscles reacted to changes in direction while the superior auricular muscles reacted to the difficulty level of the task," the study noted.
Although modern humans cannot move their ears around in the same way that dogs, cats, and horses do, these findings suggest that humans involuntarily tense their ear muscles when listening intently. "Our auriculomotor system probably tries its best after being vestigial for 25 million years, but does not achieve much," said Schröer.
"It's unclear if the muscle activity observed in the study is directly linked to the effectiveness of hearing, and it cannot be determined whether this muscle activity helped participants hear better or if it was a futile effort," the researchers stated.
"This suggests that the activity of these muscles can serve as an objective measure of listening effort and facilitate studies with other questions," they proposed.
This article was written in collaboration with generative AI company Alchemiq