Speaking of
Immediately after rehashing
'mood as error signal', I ran across
this graph of a writer's life posted by magazine writer Erin Griffith.
This is the transient response of a resonant system when switched on. In other words, a system with an internally moving template that responds partly to the error signal at each swing, gradually damping out the oscillation. Best possible illustration of the point!
More personally, the graph itself resonates with my experience as a courseware writer. Some of the details are different, but the pattern is identical.