The recent Paul McCartney concert film contains a segment featuring the ex-Beatle jamming with a friendly gorilla banging a drum-stick. The gorilla would be advised to not give up its day gig.

Watching, I am subtly reminded that part of what sets humans apart from the animal kingdom is our musical prowess. Music is ubiquitous across cultures, and we are the only species with the capacity for generating music as a form of creative expression. This suggests that humans come equipped with mental processes specialized for musical production and appreciation, just as we do for language. But, if musical appreciation lies within brain structures that all humans allegedly share, why do your musical preferences differ from everyone else’s?

To learn more about the cognitive structures motivating musical preferences, I spoke to Glenn Schellenberg, a psychology professor of at U of T’s Erindale campus. He adheres to a popular theory that we respond emotionally to a melody when aspects of the tune catch us off guard. Our reactions can be positive or negative, depending on the nature of the surprise.

Last month, Schellenberg and colleagues M. Adachi, K.T. Purdy and M.C. McKinnon published “Expectancy in Melody: Tests of Children and Adults” in The Journal of Experimental Psychology: General. The paper examines a model of what notes we expect to hear and when.

“Because a surprising experience is the flipside of an expected experience, it makes sense to study expectancies,” said Schellenberg.

Simple melodies that fulfill our expectancies completely (the notes of a scale, for example) seldom evoke emotional reactions. Likewise, when a tune has no structure, we develop no expectancies, meaning none can be denied and “the listener finds the experience unsatisfying.” Schellenberg stressed that “a good piece of music is one that denies and fulfills listeners’ expectancies in artful manner.” Expectancies may also explain why some songs are so memorable, or why we get sick of a tune after hearing it too many times.

Schellenberg finds it “interesting to examine which aspects of musical structure are learned through exposure to a particular style of music and which are innately guided.” While the types of music we listen to shape our expectancies to an extent, one of Schellenberg’s findings confirms that “people of all ages and from all cultures expect that the next notes in a melody will be close in pitch (highness or lowness) to the ones they just heard.” Schellenberg thinks that “this is an innate contribution. If it’s not, then it’s learned rapidly and easily.”

Schellenberg’s model of musical expectancy brings us one step closer to fully understanding the relationship between music and the human brain. Perhaps more research will lead to a time when we can create more evocative and enjoyable music by applying our understanding of expectancies. And on that note, professor Schellenberg adds a final comment for those interested in psychology and music: “I’m always looking for brilliant graduate students.”