Parrots and Humans Prefer Pitch Sequences of Intermediate Complexity

A well-established inverted U-shape relationship exists between stimulus complexity and human music preference, with preferences peaking at intermediate levels. We investigated whether preference for intermediate complexity is unique to humans or shared with other species. We compared the acoustic preferences of humans and budgerigars, known for their vocal learning and pattern recognition abilities, using a three-option place preference paradigm. Participants were presented with choices between computationally well-defined stimuli varying in complexity: pitch sequences with tones arranged either randomly (high complexity), into repeating patterns with changes (medium), or into a fully repetitive pattern (low). Our results demonstrate that both humans and budgerigars prefer stimuli with intermediate complexity, spontaneously exhibiting an inverted U-shape relationship between complexity and preference without any specific goal or external reward. Because a U-shape relationship has been argued to maximize learning, this preference may be of potential utility for vocal learning, however, further testing could determine whether it is also present for acoustic patterns in vocal non-learning species. Because vertebrates show inverted U-shape responses in a variety of non-auditory contexts, our findings may be rooted in general processes, but may depend on vocal learning to translate to acoustic contexts. This provides exciting opportunities to further investigate the fundamentals of vocal learning within and beyond the auditory and/or musical domain. Significance statementAppreciating music is part of what it means to be human, but it is unclear why. Comparing budgerigars - a vocal-learning parrot species - and humans, we focused on a sweet spot of musical enjoyment: We like to hear music thats not too complex and not too simple. Using a place preference setup, we showed that both species prefer to listen to pitch sequences with medium complexity relative to low or high complexity. This shared pattern suggests a fundamental cognitive principle that guides animals to stimuli that maximize learning, promoting vocal communication. Because both budgerigars and humans are vocal learners and music is a socially transmitted behavior, the appreciation of music thus may be rooted in the requirements of vocal learning.