Stolen from
this comment:
What an awesome idea to think about!
Constrained languages make it easier to standardize communication (think semantic web vs. the free web), minimizing errors of interpretation. A familiar movie-plot-structure or song-rhythm tends to put the viewer at ease and confident. At this point, it's easy to switch into "flow"y automatic mode, focusing on the higher-level structure (i.e. the meaning rather than the words). By constantly demanding your attention (though not necessarily your focus), the task puts you in a trance-like state of consciousness.
This is kinda like how driving on a highway can be relaxing.
When the medium is free-form (at least in the time dimension), one's attention is free to shift around, and one is free to spend time on complex planning, etc... it is precisely this freedom that makes anxiety possible.
I would like to look at frontal lobe activation in structured vs unstructured tasks. If my hypothesis is correct (more frontal activation in unstructured tasks), this would explain autistic impairment in the latter.
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Bluegrass seems like a very constrained form. Maybe this is my bias, since it's a style I know very well.
To test this hypothesis using information theory, I would try to show that the relevant features can be compressed quite efficiently.
If we had an MDL program for generating any tune over the space of bluegrass tunes (generating only the relevant features, let's say the kind of information that is in a MIDI file), the input necessary to generate any given tune would be rather small.