Music in its totality is a unique component of human ecology and experience (Gardiner Reference Gardiner, Lerner, Schaimberg, Anderson and Miller2003). Nevertheless, there is evidence that how the brain engages (Gardiner 2008) with music may well include adaptations of, and associations with, brain mechanisms not unique to music alone. Musical brain engagement producing emotional experience (Dewey Reference Dewey1980) may be one among many ways in which musical and other aspects of brain engagement can become deeply interrelated (Gardiner Reference Gardiner2000; Reference Gardiner, Vrobel, Rössler and Marks-Tarlow2008a). Evidence reviewed here supports the proposal of Juslin & Västfjäll (J&V) that mechanisms that are not unique to music are fundamental to emotional responses to music, but it also suggests that music adapts rather than adopts such mechanisms.

The evidence concerns the selective influence of the learning of specific musical skills on the learning of specific non-musical skills (Gardiner Reference Gardiner, Lerner, Schaimberg, Anderson and Miller2003; Reference Gardiner, Vrobel, Rössler and Marks-Tarlow2008a). For example, as discussed in Gardiner (Reference Gardiner2000) and Gardiner et al. (Reference Gardiner, Fox, Knowles and Jeffrey1996), learning musical capability has been associated with improved progress at learning arithmetic skills in first and second graders. Current work extends this to third graders as well (Gardiner et al. Reference Gardiner2008b). By contrast, effects of the same musical training on progress at reading in first and second graders have been much smaller (Gardiner Reference Gardiner2000). Capability involving musical pitch was significantly related to progress in first and second grade math, but not to progress in first and second grade reading (Gardiner Reference Gardiner2000). Rhythm skill, by comparison, was correlated weakly, but more evenly, to progress both in reading and in math. Classroom behaviors among students learning individual and group musical skills improved (Gardiner Reference Gardiner2000; Gardiner et al. Reference Gardiner, Fox, Knowles and Jeffrey1996), but those improvements did not correlate significantly to improvements either in pitch or in rhythm skills. The many skills involved in self-control and interaction with others that had to be developed as these students learned to sing alone and together, are all candidates to help explain the many improvements in students' progress in classroom behaviors that were documented (Gardiner Reference Gardiner2000).

Other investigators provide further examples of selective interaction between musical and other skill learning. Rauscher et al. (Reference Rauscher, Shaw, Levine, Wright, Dennis and Newcomb1997) have shown effects of keyboard training on preschooler's capability at assembling whole figures from parts, but not on other visuo-spatial skills. Recent studies relating musical and language development concern improvements at engagement with rapidly changing signals (Gaab et al. Reference Gaab, Tallal, Kim, Lakshnariyann, Glover and Gabrielli2005; Tallal & Gaab Reference Tallal and Gaab2006).

Selective associations between musical and other skill learning cannot be explained by changes affecting processing globally; but the associations can be due to, and signal similarities in, the ways in which the brain of a learner becomes engaged through related processing in order to achieve capabilities in different skill domains (Gardiner Reference Gardiner2000; 2002; Reference Gardiner, Vrobel, Rössler and Marks-Tarlow2008a). Capability in every skill can depend critically on finding a way of engaging mentally to support what is desired (Gardiner Reference Gardiner, Vrobel, Rössler and Marks-Tarlow2008a). As chess studies have illustrated, improvements can be caused by and even depend on qualitative changes in how engagement is carried out (Chase & Simon Reference Chase and Simon1973; DeGroot Reference DeGroot1965). The selective cross-relationships between musical and other learning can show that an important strategy within our development of mental engagement is learning how to adapt similar, though typically not identical, brain processing components and strategies to different applications. The human development of music could, indeed, have depended on capability for such adaptation.

Our survival as a species has depended on evolving and developing certain means of mental engagement that support the personal and social capabilities critical to our survival. Music can be explained as illustrating that our inventive brains can adapt brain capabilities we needed to evolve in order to survive to develop new opportunities that we discover to enrich our lives, even if not in ways as critical to our survival (Gardiner Reference Gardiner, Lerner, Schaimberg, Anderson and Miller2003; Reference Gardiner, Vrobel, Rössler and Marks-Tarlow2008a). Many of J&V's examples relating musical engagement and emotion can viewed in this way.

What J&V term “emotional contagion” seems the most important of the ways proposed to connect music listening to emotional experience. I propose a way of framing that can aid further investigation of such emotional reactions to music: this is, to think of such reactions to music as an adaptation of a more general capability for detecting and reacting to signaling by sounds that express emotion. This ability could have been critical to human evolution.

Emotion and physiological and behavioral changes are deeply interconnected, as James and Lange (Reference James and Lange1922), Cannon (Reference Cannon1929), and many others more recently have emphasized. Emotional expression refers to such changes perceivable by an observer. An individual may try to hide evidence of his or her emotion; but emotional expression can have enormous communicative value as well. Facial expression has been especially well studied (Ekman Reference Ekman1997); but, likewise, a baby's cry, a scream of fear, or a sigh of pleasure can be not only emotional reactions but also signals. Our success as a species – physically weaker, individually, but stronger in our group interactions than our competitors – could have been aided enormously by developing rich capabilities both at expressing and perceiving signs of emotion as signals.

We should not think of music in the abstract merely as sound, but rather remember that it has developed as a product of human acts, part of whose purpose has often included the communication of emotion. J&V propose that the processes involved in the emotional experience of a music listener are “somewhat different” from those involved in generating emotional expression in the music. Nevertheless, I doubt that an engagement with music that detects emotional signals is unrelated to an engagement with music that produces signals conveying emotion. Thus, studies that relate the emotions perceived by people to the acts they make (e.g., Clynes Reference Clynes1977) may be very linformative.

Learning experiments involving music may help to illuminate the connection between emotional expression and emotion as signal. The ability to compose or perform music that conveys emotion improves with learning. Musicians have to learn to judge from their own and listeners' reactions in what way, and how effectively, they are communicating emotion. Comparing music-making gestures when emotional signaling seems especially powerful with instances when music becomes “just notes” may well provide useful clues to differences in the underlying engagement. Our languages for emotional communication are rich and subtle. Music may be of great aid in their investigation.