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ceptually and in terms of their underlying acoustic attributes, they are useful both for musical expression and for creating well-controlled experimental stimuli in order to understand how the brain processes timbre.
An ERP study compared the three dimensions of timbre (attack time, spectral centroid, and spectral flux) directly using mismatch negativity (MMN), a negative ERP that occurs around 200 ms after any small deviations from the sound context. The MMNs elicited by the different dimen- sions were indeed separate in their underlying neural sources, suggesting separate dimensions of processing in auditory memory and providing convergent results with the psy- chophysical data (Caclin et al., 2006). An functional MRI experiment showed that modulations in spectral shape elic- ited right-lateralized brain activity in the superior temporal sulcus (STS), an area immediately below the STG (Warren et al., 2005). This right-lateralized STS activity supports the idea that the right hemisphere is relatively tuned to spectral changes, whereas the left hemisphere is more tuned to fine- grained temporal structure (Flinker et al., 2019).
Because timbre is an important cue toward the perception of auditory objects, the study of “dystimbria,” or the impair- ment of spectral and temporal analysis without loudness or pitch-processing difficulty (Griffiths et al., 2007), can provide a window into how the brain perceives objects from the world of sound. On the other hand, people with exceptionally fine- grained training in listening to timbres, such as piano tuners, have enhanced gray matter in the superior temporal struc- tures as well as in the hippocampal complex, which is crucial for learning and memory (Teki et al., 2012). These gray matter differences are correlated with the duration of one’s career in piano tuning and not with actual age, suggesting that there are adaptations in brain structure that come with advanced musical experience, even within the specific task of listening for timbre in order to tune a musical instrument.
Beat is the basic building block of musical rhythm that allows for the synchronization of musical events. Beat not only synchronizes musical events to one another but also synchronizes our brains to the rhythm of musical stimuli. When presented with a beat, EEG recordings show rhythmic activity at the beat frequency (Nozarandan et al., 2011). This neural sense of beat is produced through the coupled oscilla- tion of auditory and motor pathways, including motor areas
of the brain (Grahn and Brett, 2007), that could be respon- sible for the ability to predict a pulse even in situations where there is no spectral energy produced on the beat itself (Tal et al., 2017). The motor system contributions to beat percep- tion are particularly apparent in classical musicians and in patients with Parkinson’s disease. Parkinson’s patients, who have multiple motor deficits, are impaired at discriminating beat-based rhythms but not rhythms that lack an underly- ing beat (Grahn and Brett, 2009). This suggests an important role of the motor system in the detection and generation of internal beats.
The coupling between the auditory and motor systems when confronted with beat-based stimuli might explain why we feel “groove,” which is defined as the pleasurable urge to move to music. Music that is rated as high in groove elicits larger motor-evoked potentials (electrical fluctuations measured from motor neurons in the hand and arm) in musicians than low-groove music or noise (Stupacher et al., 2013). One fea- ture that determines the sensation of groove is syncopation, which can be defined as a slight violation of an expected and beat-based rhythm. However, this is not to say that higher syncopation necessarily means a higher sense of groove. In fact, an inverse U-shaped relationship between groove and syncopation has been observed, with medium-syncopated music tending to elicit a stronger desire to move than either high- or low-syncopated music (Witek et al., 2014).
In addition to being pleasurable, it is well known that rhythm can synchronize large populations of people, motivating them to movement. Recent research is addressing whether synchronous, rhythmic movement can affect social behav- ior. In a sample of 14-month-old infants, parents holding the infant faced an experimenter and moved either syn- chronously (onbeat) or asynchronously (offbeat) from one another. Infants proceeded to be more helpful toward the experimenter after the synchronous condition compared with the asynchronous condition (Cirelli et al., 2014). This remark- able finding demonstrates the social value of synchronizing to a beat, even during infancy.
Meter refers to the hierarchical organization of beats into recurring groups. Meter usually consists of groupings of two, three, or four beats, although in some cases rarer meters that contain five, seven, or even larger or variable sets of beats may occur. Regardless of the number of beats, there is a ten- dency to have an accent on the first beat of a given measure
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