Consciousness Blog 13 February 2016
Recent research has however begun to elucidate the neural processes that are involved in human appreciation of music. Published in Neuron, Volume 88, Issue 6, p1281–1296, 16 December 2015, an article 'Distinct Cortical Pathways for Music and Speech Revealed by Hypothesis-Free Voxel Decomposition', by Sam Norman-Haigner, Nancy G. Kanwisher and Josh H. McDermott, of the Massachusetts Institute of Technology, reports on the identification of distinct cortical pathways for speech and music in the auditory cortex. Previous work by the same team reported in The Journal of Neuroscience in 2013, also using fMRI scanning, had identified specific regions of the auditory cortex that respond exclusively to clearly pitched harmonic tones, known as 'resolved' tones, as distinct from pure frequency-based 'noise'. In a normal human, the process of harmonic resolution is carried out within the cochlea, so that input to the auditory cortex is 'resolved' where that is neurally feasible.
Through a crowd-based survey, the researchers identified 165 sound clips of two seconds each, representing a thorough overview of types of sound input, including speech and music, and observed the fMRI response to this range of sounds in human subjects. The experiment resulted in the identification of clearly distinct regions of the auditory cortex for speech and music. "This analysis revealed six components," say the researchers, "each with interpretable response characteristics despite being unconstrained by prior functional hypotheses. Four components embodied selectivity for particular acoustic features (frequency, spectrotemporal modulation, pitch). Two others exhibited pronounced selectivity for music and speech, respectively, and were not explainable by standard acoustic features."
The research supports the idea, obvious to many commentators, that music and rhythm had a role in socialization from very early on in evolution: you have only to think of bird-song or whale-song, and mating rituals in numerous animal species. Darwin wrote in The Descent of Man and Selection in Relation to Sex: "the males sometimes pay their court by dancing, or by fantastic antics performed either on the ground or in the air. With birds of paradise a dozen or more full-plumaged males congregate in a tree to hold a dancing-party, as it is called by the natives: and here they fly about, raise their wings, elevate their exquisite plumes, and make them vibrate, and the whole tree seems, as Mr. [Alfred] Wallace remarks, to be filled with waving plumes…One observer, who kept several pairs alive, did not doubt that the display of the male was intended to please the female."
harmonies and rhythm are two different things, of course, and it is not
clear that many or any pre-human species combined them into dance as we
understand it, although some bird species seem to come close to it; but
what is clear is that when groupish behaviour came along, it enlisted
music and dance as means of strengthening the bonds between group members.
One stream of research would have it that the combination of musical and
motor skills that is required for dancing arose in human and bird species
because both are 'vocal learners', whereas pre-human primates had relatively
unsophisticated vocal skills. However that theory does not sit well with
plentiful research showing an abundance of 'CV's (conspecific vocalizations)
in non-human primates, see e.g. Pascal Belin, Voice processing in
human and non-human primates, Philos Trans R Soc Lond B Biol Sci.