This 2018 UK review subject was colored-hearing arising on hearing music:
“Music-colour synaesthesia has a broad scope encompassing not only tone-colour synaesthesia elicited on hearing individual tones, but a complex and idiosyncratic mixture of phenomenological experiences often mediated by timbre, tempo, emotion and differing musical style.
The possession of synaesthesia or absolute pitch was shown to have very little effect on the actual colours chosen for each of the musical excerpts, but it might be reasonable to expect that music that elicits a strong emotional response may be more likely to induce synaesthesia than music that does not.
The examination of eight neuroimaging studies were found to be largely inconclusive in respect of confirming the perceptual nature of music-colour synaesthesia. Neither the hyperconnectivity nor the disinhibited feedback theory currently holds as a single categorical explanation for synaesthesia.
Theories promoting the notion of ‘ideaesthesia’ have highlighted the importance of the role of concept and meaning in the understanding of synaesthesia..and a replacement definition: Synaesthesia is a phenomenon in which a mental activation of a certain concept or idea is associated consistently with a certain perception-like experience.”
The review cited other interesting reviews, including The Merit of Synesthesia for Consciousness Research. The cited “eight neuroimaging studies were found to be largely inconclusive” and much of the review was philosophizing and casting around for clues.
One relevant element missed by the underlying research and the review was critical periods of human development. A cited reference in How brains mature during critical periods was Sensitive periods in human development: Evidence from musical training (not freely available) which illuminated some aspects of the research:
“In contrast to a critical period, where a function cannot be acquired outside the specific developmental window, a sensitive period denotes a time where sensory experience has a relatively greater influence on behavioral and cortical development. Sensitive periods may also be times when exposure to specific stimuli stimulates plasticity, enhancing changes at the neuronal and behavioral levels.
The developmental window for absolute pitch may be more similar to a critical than a sensitive period.
The auditory cortex appears to have an unusually long period of developmental plasticity compared with other sensory systems; changes in its cellular organization and connectivity continue into late childhood.
The effects of musical training have been shown to impact auditory processing in the brainstem as well.”
Let’s say that a researcher wants to examine, for example, absolute pitch, a rare trait, present in a subset of synesthetes – music-color, another rare trait. The study as designed would probably be underpowered due to an insufficient number of subjects, and it would subsequently find “very little effect.”
Let’s say another researcher focused on brain areas in the cerebrum, and like the eight cited studies, ignored the nuclei in the pons part of the brainstem which are the first brain recipients of sound and equilibrium information from the inner ear via the eighth cranial nerve. Like those studies, they were also biased against including other brain areas that would indicate “a strong emotional response.” A study design that combined leaving out important brain-area participants in the synesthesia process with a few number of synesthetes would be unlikely to find conclusive evidence.
The reviewer viewed the lack of evidence from “eight neuroimaging studies” as indicating something about the “perceptual nature of music-colour synaesthesia.” An alternative view is that the lack of evidence had more to do with study designs that:
- Had a small number of subjects;
- Didn’t investigate likely music-color synesthesia development periods;
- Omitted relevant brain areas; and
- Didn’t investigate associations of music-color synesthesia with epigenetic states.
Does an orangey twilight of fading sunflowers help you feel?
https://www.sciencedirect.com/science/article/pii/S1053810017305883 “Music-colour synaesthesia: Concept, context and qualia” (not freely available)