Two important concepts in my current hypotheses about the nature of music are State of Mind and Infant Language Acquisition.
In this article I list three groups of academic researchers whose investigations deal with these concepts and relate them to music in a manner which shares some common ground with my own theory.
State of Mind
My current working hypothesis is that the primary effect of music, and also its primary biological function, is to induce an altered state of mind.
To make this hypothesis complete, it is necessary to specify what it is about the "musical state of mind" which is different from the ordinary "non-musical" state of mind.
Based on observations about the use of music in films, and my own subjective experience, I have developed the more specific hypothesis that music encourages a partial disconnection from immediate reality, and intensifies emotions that we feel when thinking about things beyond our immediate reality, ie in our daydreams.
But regardless of this detail, the limited assumption that the consequent state of mind is the primary thing is itself significant. If music only matters because of how it affects us, then the actual content of music has no intrinsic meaning, and whatever the rules are that define music, they must be the result of some accidental evolutionary contingency.
I have so far found two instances of academic researchers who have reached conclusions suggesting that the purpose of music is to induce a certain state of mind.
Ruth Herbert: Dissociation and Absorption
Ruth Herbert is a research fellow at Oxford University whose research interests include "psychological processes involved in everyday listening", and in particular "trancing, dissociation and absorption".
Her publications on this particular topic include Conceptualizing the Subjective Experience of Listening to Music in Everyday Life, Modes of Music Listening and Modes of Subjectivity in Everyday Life and her book Everyday Music Listening (Absorption, Dissociation and Trancing)
Part of my hypothesis about the effect of music is that it induces a tendency to partially disconnect from immediate reality, which would appear to be very similar to what Herbert calls "dissociation". Also I relate disconnection from immediate reality to "connection" to the music, which relates to Herbert's concept of "absorption".
Perlovsky and Masataka: Cognitive Dissonance and Cognitive Interference
Perlovsky and Masataka's research relates to situations where some type of psychological conflict is induced in the experimental subjects, and music appears to resolve this conflict in one particular direction.
For example, in the cognitive dissonance scenario, child subjects are asked not to play with their second-favourite toys (from a group of available toys), and the conflict is between their desire to play with the second-favourite toys, and the fact that actually they are not playing with those toys (given that they comply with the request not to play with them). This conflict is tested when subjects are asked how much they like playing with the toys that they originally reported as being their second best toys. If music is played, the conflict is more likely to be resolved in favour of what they desire, ie playing with the toys, as opposed to what is real ie not playing with the toys.
In the cognitive interference scenario, the conflict is based on an example of the "Stroop interference task", where subjects are asked to identify the colour of some words, where the words themselves describe some other colour, eg RED, or YELLOW. In this scenario, music helps the subjects to resolve the conflict in favour of the correct answer, ie the actual colour, rather than the interfering content of the words.
Neither of these two scenarios appears to relate directly to my hypothesis that music helps the listener to more fully experience the emotions of daydreams. But they can be both be interpreted in terms of psychological conflicts, and it is also possible to interpret the experience of emotions in daydreams as the resolution of a psychological conflict.
In the case of daydreams, the conflict is a conflict between reality and fantasy: "reality" tells the daydreamer that the content of the daydream is not real, therefore the emotions should be limited by their non-reality, whereas "fantasy" says that, temporarily, the daydream is to be perceived as much as possible as if it is real, and this includes the emotions. With this interpretation, music resolves the conflict in favour of "fantasy" and against "reality".
In all of these three scenarios, there is an identifiable psychological conflict, and music helps to resolve that conflict in one particular direction.
A possible conclusion is that there is some more general underlying principle in all three scenarios, which describes a certain class of psychological conflicts, and where music resolves such conflicts in favour of one of the tendencies in the conflict, and against the opposing tendency.
(Additionally, we can directly relate the daydream scenario and the compliance-based cognitive dissonance scenario, if we suppose that the children actually daydreamed about playing with the toys that they weren't playing with, since the music would then cause them to more fully experience the positive emotions of that hypothetical experience of playing with those toys.)
Infant Language Acquisition
How a "State of Mind" Hypothesis Leads to Consideration of Infant Language Acquisition
If the purpose of music is to induce a certain state of mind, then the actual content of music is less relevant.
Even across different cultures, music has various specific aspects, such as melody, and scales, and rhythm. None of these aspects appear to define any specific meaning, and the content of music appears to be solely determined by the requirement to be musical.
From a purely evolutionary point of view, these aspects of music, which are simultaneously very specific yet apparently meaningless, would appear to require some explanation. One thing we might look for is something else in human thought or behaviour which is "like" music, which music could have evolved from. That is, a musical pre-cursor.
The Most Obvious Candidate for a Musical Pre-Cursor
As it happens, there is one other thing which is very much "like" music, and that thing is Language. If there is an evolutionary relationship between the apparently arbitrary requirements of music, and some other aspect of human nature, that other aspect is probably language.
A more detailed hypothesis, based on consideration of various specific relationships between musical aspects and speech aspects, and also deeper patterns found in the different relationships in each case, ie musical rhythm compared to speech rhythm versus musical melogy compared to speech melody, is that music has evolved from language by adding at least one additional constraint to a built-in language "recognizer".
Such a language recognizer most plausibly exists as part of our initial language acquisition process, ie for when we are infants. The job of such a recognizer is simply to recognize language, when it occurs, based on simultaneous occurrence of expected components of language.
The recognizer does not carry any strong assumption about what language should be (ie no "Universal Grammar"), but it does carry an implicit assumption that there is a thing which is language, which needs to be understood and processed by the infant's mind as a thing which is separate from all other things, and which merits a certain amount of attention and concentration when it does occur.
Given this assumption, it is plausible that the built-in recognizer has the effect of altering the infant's state of mind in a manner which helps the infant to more quickly learn its native language. And this relationship between language recognition and an altered state of mind could have evolved into a relationship between music recognition and a similar altered state of mind.
I have not found any academic research that has discussed this particular hypothesis about the relationship of music to infant language acquisition, however I have found one paper that does discuss in detail a slightly different hypothesis about the relationship between music and infant language acquisition.
Anthony Brandt: Musical Ability Underlies Language Acquisition
In support of their hypothesis, Brandt et al document all the various similarities and parallels between music and language, in particular where those similarities and parallels relate to language acquisition.
Their view is distinct from my hypothesis about the relationship between music and language acquisition, in that they do not appear to regard music as a separate "thing" which needs to be explained, rather they treat it as an intrinsic component of language acquisition.
In particular, Brandt et al's hypothesis, that music exists to support early language acquisition, fails to explain why people should continue to want to listen to music long after they have become fluent in the various "musical" aspects of their native language. (In their paper they do acknowledge, to a very limited extent, that the response to music is something that persists long after the stage in early language acquisition where they consider music perception to be relevant, but they do not highlight that as a major difficulty in their theory.)