Learning mechanisms in the brain
Mapping the tonal hierarchy in the brain
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The tonal hierarchy is a perceptual concept that organizes the notes of the western major and minor scales (those scales investigated so far) as more or less stable. Notes that make up the tonic chord are most stable, followed by other notes in the scale, with non-scale notes being the least stable. This hierarchy is learned implicitly, meaning there's no need to know anything about music theory to know that a note "fits" - or doesn't. Previous work has attempted to map the tonal hierarchy, a robust behavioural construct, in the brain based on various event-related potentials. For example, the early right anterior negativity (ERAN), which has been interpreted as an index of musical grammar, where in short, ungrammatical chords elicit an ERAN; grammatical chords do not. The 2021 paper co-authored by Sarah called Mapping tonal hierarchy in the brain hypothesizes a link between ERAN amplitude and scale degree; instead, it finds that only scale and non-scale tones can be differentiated. Other work does find a link between scale degree and various ERPs.
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Together with Danica Robichaud, an honours student in the CAANLab at Memorial University of Newfoundland, we are extending the 2021 paper to include an active task, while controlling for auditory confounds raised by reviewers of the published study. Future projects along this line of research might include replicating existing findings on this topic, testing new paradigms and/or analyses, extending to different scales, or other student or collaborator interests.
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Creating a new tonal hierarchy
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Investigating how something like the tonal hierarchy, which is quite complex, is created in our minds is another interesting line of research. Since most people are quite familiar with western music and the major scale, that kind of music can't be used to study the emergence of such a system. Instead, artificial grammars are created. An artificial grammar means that for each note, how they fit with each other – what’s “in-key”, what’s “out-of-key”, what can come after what is prescribed by an algorithm. That way, the music is completely new to anyone who hears it. Previously, with the help of Praveena Satkunarajah (PhD student in CAANLab), an artificial grammar was created to be similar in complexity to the western tonal system. Participants were exposed to this new type of music and then asked to rate each note's fit in the system's scale. So far, a study with 30 minutes of exposure found that this was insufficient for the listeners to pick up on the underlying statistical structure of the grammar. Future projects might include longer exposure times, the inclusion of harmony, and manipulation of the grammar itself, as well as the addition of EEG to see how long it takes to detect a hierarchy like the western tonal hierarchy (this is dependent on the outcome of the above line of research).