https://phys.org/news/2018-06-laurel-yanny-repetitions.html

"There's this neat auditory illusion called the Speech-to-Song Illusion that musicians in the '60s knew about and used to artistic effect—but scientists didn't start investigating it until the '90s," said Michael Vitevitch, professor and chair of psychology at KU, who conducted the study with undergraduate and graduate student researchers in the department's Spoken Language Laboratory. "The illusion occurs when a spoken phrase is repeated— but after it's repeated several times it begins to sound like it's being sung instead of spoken."

The KU researcher said previous studies have looked at characteristics of phrases that contribute to the illusion and have elicited the phenomenon in speakers of English, German and Mandarin. Further studies have shown brain regions that process speech to be active when a phrase is perceived as speech while brain regions that process music fire when the phrase is heard as song.