Have you ever wondered why certain pop songs just make you feel so good?
Researchers studying the question found that the right combination of uncertainty and surprise is what gives listeners the most pleasure.
The study, published in the journal Current Biology, involved an analysis of 80,000 chords in 745 pop songs from the US Billboard "Hot 100" chart between 1958 and 1991.
The researchers -- from institutes in Germany, Norway, Denmark and the UK -- used a machine-learning model to quantify the level of uncertainty and surprise of these chords, and then asked 39 adult volunteers to rate how pleasurable they found each series of chords.
Each song was stripped of its melody and lyrics so that only chord progressions were left and the results couldn't be skewed by other associations to the songs that listeners might have had.
skew[skjuː]: v. 偏离，歪斜；扭转，偏转；歪曲
They found two things: that participants derived greater pleasure when they were relatively certain what would happen next but then were surprised by an unexpected chord progression.
However, the same number of participants found it pleasant when they were uncertain as to what would follow, and then the subsequent chords were more familiar to them.
"It is fascinating that humans can derive pleasure from a piece of music just by how sounds are ordered over time," Vincent Cheung, the lead researcher on the paper from the Max Planck Institute for Human Cognitive and Brain Sciences, Germany, said in a statement.
"Songs that we find pleasant are likely those which strike a good balance between knowing what is going to happen next and surprising us with something we did not expect. Understanding how music activates our pleasure system in the brain could explain why listening to music might help us feel better when we are feeling blue."
Cheung told CNN that pleasure in music is linked to expectancy. Previous studies had looked into the effects of surprise on pleasure, but he and his colleagues' study also focused on the uncertainty of listeners' predictions.
The songs used in the experiments included James Taylor's "Country Roads," UB40's "Red, Red Wine" and The Beatles' "Ob-La-Di, Ob-La-Da."
用于实验的歌曲包括詹姆斯·泰勒的《Country Roads》、UB40乐队的《Red, Red Wine》和甲壳虫乐队的《Ob-La-Di, Ob-La-Da》。
The findings may help improve artificial musical algorithms and could help composers write music or predict musical trends.
"The idea is that hopefully as a scientist analyzing these patterns of pleasure in humans, you can somehow work out where music can go next," Peter Harrison, a researcher at Queen Mary University, London, who worked on the project, told CNN.
As part of the same experiment, the researchers also used brain imaging to locate the areas of the brain reflected in musical pleasure.
They found the regions involved were the amygdala, the hippocampus and the auditory cortex, which process emotions, learning and memory, and sound, respectively.
Cheung added that another part of the brain, the nucleus accumbens -- which processes reward expectations -- was perhaps responsible for "directing our attention towards the music so that we will try to find out what will happen next."