Juslin & Västfjäll (J&V) present a framework within which “musical emotions” can be organized. They propose six mechanisms to explain how music elicits emotions in listeners. One mechanism J&V propose is the process of emotional contagion, whereby we internally mimic the emotional content of music via mirror neurons, resulting in the experience of the same emotion as conveyed through the music. They argue that the voice-like qualities in music arouse us, and that we process music as we would a super-expressive voice. According to super-expressive voice theory (Juslin et al. Reference Juslin and Sloboda2001), we process a musical piece as if it were a voice. Although there is preliminary evidence that perception of emotion in music and in the voice share some of the same brain areas (e.g., Nair et al. Reference Nair, Large, Steinberg, Kelso, Stevens, Burnham, McPherson, Schubert and Renwick2002), we report evidence of distinctions.
Recent functional magnetic resonance imaging (fMRI) studies indicate that there are specific parts of the brain, including the superior temporal sulcus, that respond selectively to human voices (Belin et al. Reference Belin, Zatorre, Lafaille, Ahad and Pike2000). Moreover, electroencephalogram (EEG) research reveals that such processing is faster and more extensive for vocal than for non-vocal sounds (Schirmer et al. Reference Schirmer, Simpson and Escoffier2007). These two findings suggest that our brains can differentiate between emotional voice sounds, and emotional musical sounds, very early in processing.
Studies of patients with brain injuries provide further evidence of the distinction between the processing of voices and non-voices. Griffiths et al. (Reference Griffiths, Warrent, Dean and Howard2004) describe a patient who underwent a stroke that resulted in damage to his left insula and left amygdala, and consequently possessed a deficit in “musical emotion” processing, while retaining normal music perception and voice prosody perception. If the same mechanism is responsible for both processes, how can one be impaired and the other intact? This indicates that separate neural networks may underlie voice prosody and musical emotion perception.
A dissociation was also found in patient I.R., who suffered damage to her left superior temporal gyrus and left insula, among other regions, resulting in the loss of music recognition, while leaving musical emotion perception and speech prosody intact (Patel et al. Reference Patel, Peretz, Tramo and Labreque1998; Peretz et al. Reference Peretz, Gagnon and Bouchard1998). Although patient I.R. correctly discriminated the emotional nature of musical excerpts, she claimed that she was only guessing, and was surprised to learn that she was doing well. It therefore appears that her discrimination ability was outside of her awareness or intention (Peretz et al. Reference Peretz, Gagnon and Bouchard1998). This is strikingly similar to the phenomenon of blindsight, in which patients are able to respond to visual stimuli, but are not consciously aware of perceiving them (Weiskrantz et al. Reference Weiskrantz, Warrington, Sanders and Marshall1974). Interestingly, I.R.'s speech prosody judgments were normal (she did not have to “guess”). The fact that emotion perception in music was outside of awareness, while emotion perception in the voice was within awareness, is further evidence of distinct systems for voice prosodic processing and musical emotion processing.
Another problem with the emotional contagion mechanism is that it fails to explain emotional reactions to music that are not congruent with the emotional content of the music. For example, when watching a frightening movie and you hear an angry voice, or a “threatening” musical excerpt, this theory predicts that you should also feel angry. However, this is not the case; instead, we feel fearful. From an evolutionary perspective, it would not be adaptive to possess a simulation mechanism that causes you to become angry upon hearing an angry voice or other threatening sound. Therefore, this theory fails to take into account all types of emotional expressions.
J&V present a thoughtful list of mechanisms responsible for musical emotions. Such a framework is much needed, and undoubtedly will be informative for guiding future studies. However, there are weaknesses in one of the proposed mechanisms – emotional contagion – that need to be addressed. One possibility is that the same underlying mechanism is responsible for both musical and vocal emotional expressions, as super-expressive voice theory postulates, but that the former is more sensitive to damage than the latter. Further studies must directly compare “musical emotions” and vocal emotions to elucidate these differences.
