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Figure 3. A schematic model of neural entrainment. Endogenous neural oscillations (see text for details) experience a phase reset following a sequence of regularly spaced salient events (e.g., beats in music). These events tend to be heard but they can also arise from vision and touch. After a phase reset, the synchronized oscillations are considered to be entrained. The neural entrainment continues through a rest in the music (i.e., it persists after the sensory stimulation ends).
required for expert music performance, particularly in con- tinuous pitch instruments like the voice or violin (Loui, 2015).
Let us define the beat here as a pattern of perceptual accents that occur at equally spaced time intervals across a rhythmic sequence. It is important to note that by invoking the notion of a perceptual accent, the beat is ultimately a psychological construct (London, 2012). There are several reasons for con- sidering the beat in this manner. First, the perceptual accents need not be physically prominent (i.e., louder or longer). Second, the beats of a rhythm do not always coincide with events of a rhythm. Third, the feeling of the beat can persist even after the music stops.
A neurocognitive view of beat perception suggests that the beat emerges from the entrainment of endogenous (i.e., internally generated) neural oscillations. This process, referred to as neural entrainment, is depicted in Figure 3. The starting point for understanding neural entrainment is noting that it is well- known that neurons exhibit endogenous oscillatory activity, regardless of whether or not these neurons are part of a system that is currently “online.” These neural oscillations exhibit their own frequency and phase characteristics. However, after an observer perceives a few regularly spaced perceptually salient events, a phase reset may occur wherein the endogenous oscil- lations that are of a similar frequency to the frequency of the perceptually salient events become phase aligned (Obleser et al., 2017). At this point, the neural oscillations are said to be entrained. Remarkably, this entrainment of neural oscillations
will continue to be sustained even after a beat has stopped. Open questions in this subtopic of rhythm research include the extent to which this neural entrainment persists and the extent to which it is possible to entrain to rhythms that are presented through nonauditory modalities (Iversen et al., 2015).
Feeling the Music
Because all sound arises from mechanical vibration, one might expect that music should be perceptible on the basis of mechanical vibration on the skin (see the example with a cello in Figure 4). Like the sensory hair cells that exist in the cochlea of the inner ear, mechanoreceptors found in the dermis layer of the skin are responsible for the transduction of vibrotactile stimuli. Four classes of mechanoreceptors have been identified that are sensitive to vibrotactile input (Bolanowski et al., 1988). Each class has its own characteristic frequency and frequency range. Because of these physiology foundations, there appears to be some capacity to represent the spectral properties of a vibrotactile stimulus even at the level of the skin.
Georg von Békésy, the Nobel Laureate biophysicist who has arguably had the most lasting impact on auditory research (see acousticstoday.org/7302-2 for a short biography), con- ducted a series of experiments that involved mechanically stimulating skin on the forearm to assess different models of cochlear function (von Békésy and Wever, 1960). These particular experiments led him to conclude that the fre- quency response corresponding to the place of maximal excitation in a traveling wave was sharpened through a
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