When singers belt out high notes their eyebrows also move higher than they do when they sing low notes, reveals a new study.
While that may not be an absolute physiological rule, a team of Danish and American researchers discovered that it happens quite consistently.
The eyebrow/high-note evidence comes from "an experiment lasting less than one minute."
Sofia Dahl at Aalborg University Copenhagen, and David Huron and Randolph Johnson at Ohio State University, ran their experiment 44 times, each with a different volunteer, the Guardian reported.
They asked each person to sing, but purposely did not solicit any information as to whether anyone had musical training.
The experiment was simple and quick. To prompt each volunteer to sing, Dahl, Huron or Johnson used this script: "I want you to sing a comfortable pitch and sustain it while we take your picture. Sing whatever vowel you like. Now hold the note ... [Take picture]. Now I want you to sing a higher [lower] pitch - the highest [lowest] pitch you can. Good. Now hold it. [Take picture]"
The research team then showed the photographs to judges who had not been present during the vocalisation.
The results were apparently stark. The report asserts the "independent judges selected the high-pitch faces as more friendly than the low-pitch faces. When photographs were cropped to show only the eye region, judges still rated the high-pitch faces friendlier than the low-pitch faces."
Building on a mound of earlier research that is documented in the scientific literature, Dahl, Huron and Johnson assessed the brow/pitch behaviour they saw and heard.
Their data, they conclude, is "consistent with the role of eyebrows in signalling aggression and appeasement."
The prior work by others gathered evidence about the role or roles eyebrows play in expressing human emotion.
This new study mentions a discovery in 1978 that "raised or arched eyebrows are indicative of appeasement or friendliness," a 1979 finding that "when angry, the eyebrows are lowered, resulting in a more pronounced brow ridge", and a 1981 treatise explaining that in many cultures lowered eyebrows are "interpreted as displays of greater dominance or aggression".
The study has been published in the journal, Empirical Musicology Review.