Brain Recognizes Musical Rhythms Following Simple Integer Ratios
A study conducted by a team of researchers from MIT devised a way to reveal a person's biases in the brain's interpretation of sensory input. The researchers found out that the brain recognizes musical rhythms following simple integer ratios and is influenced by the exposure to the preferred type of music.
In order to understand how the brain interprets sensory input like musical rhythms, the researchers looked into the concept of priors. Priors are biases thought to be based on past experiences of the person in the world. Priors also help people to make sense of ambiguity perceived in life by finding familiar speech sounds, words, or linguistic forms based on a person's biases.
The study published in the January issue of Current Biology tested both Westerners and a remote Bolivian tribe, the Tsimane, in order to reveal priors for musical rhythm. The researchers also tested for the priors on musicians and non-musicians.
The MIT team conducted the test by first asking American students to listen to a randomly generated series of four beats after which the students are asked to tap back the rhythm they thought they heard. The researchers recorded the student's tapped rhythm and were played back to the students to be tapped out again.
Following a series of iterations, the researchers found out that the tapped out rhythm of the students changed slightly and was eventually dominated by the students' internal biases. By doing the procedure many times, the researchers, Nori Jacoby and Matthew McDermott, was able to measure the biases for the simple rhythms.
Jacoby and McDermott found out that rhythms tapped out by the students follow simple integer ratios. These integer ratios are also common in the rhythms found in Western Music. These meant that the priors for musical rhythm are influenced by the listener's exposure to a certain type of music, Western Music. This was further proven when the researchers tested for priors for musical rhythm between musicians and non-musicians suggesting priors are formed through the listening of music rather than creating music.
The same was done to the remote Bolivian tribe of the Tsimane. The Tsimane tribe has little to no exposure to Western music. Doing the same procedure to the Tsimane, the team found out that although the musical rhythms were different from the musical rhythms commonly found in Western music, the Tsimane musical rhythm still follows simple integer ratios.
The rhythms favored by the Tsimane are consistent with the known music of the tribe as documented in a few records that exist. This further proves that priors of musical rhythms are based on exposure to music and that regardless of music type people are exposed to, the musical rhythms follow small integer ratios.
In an interview with MIT News, Jacoby says, "It's a way to probe the mental representation of what people unconsciously expect. We wanted to find a way to 'read their minds', but without requiring people to introspect or verbalize anything." The researchers are looking into delving prior of musical rhythms across different cultures in future studies.