How attention and beat perception modulate neural entrainment to rhythm

Recently, steady-state evoked potentials (SS-EPs) at the frequency of the beat have been observed in electroencephalograms (EEG; Nozaradan et al., 2011, 2012). Previous studies involved participants actively attending to isochronous sequences and repeating rhythms. Here we assessed whether neural enhancement of SS-EPs at beat-related frequencies occurred when (1) participants did not attend to the rhythms, and (2) the rhythm was novel and did not repeat. When participants listened to rhythms that contained a beat SS-EP enhancement was larger during attended rhythms than when participants were distracted by another task, although SS-EPs were still present in all conditions. SS-EP enhancement therefore occurs in non-repeating rhythms, providing further evidence of SS-EPs as a marker of beat perception. Greater response in attended conditions suggests that attention may be a necessary component of beat perception

Investigating how neural entrainment relates to beat perception by disentangling the stimulus-driven response

Beat perception – the ability to perceive a steady pulse in music – is nearly ubiquitous in humans, but the neural mechanisms underlying this ability are unknown. A growing number of electroencephalography (EEG) studies suggest that beat perception is related to neural entrainment, a phenomenon in which cyclic changes in the excitability of populations of neurons synchronize with a rhythmic stimulus. However, the relationship between acoustically-driven and entrainment-driven neural activity is unclear. This thesis presents EEG research that extends our understanding neural entrainment is related to beat perception by characterizing, equating, and finally removing the stimulus-driven response in the neural signal isolating the entrainment-driven responses. Chapter 1 presents a general overview of how neural entrainment may relate to beat perception, the common methods of measuring neural entrainment, and current debates in the literature about how best to account for the stimulus-driven response in the neural signal and also what the neural power spectrum reflects. Chapter 2 presents research on how perceptual and acoustic factors in auditory stimuli influence neural spectral power in a series of experiments in which beat strength, tone duration, and onset/offset ramp duration were manipulated. The results suggest that both perceptual and acoustic factors influence neural spectral power, and that accounting for the stimulus-driven response in the neural spectrum is more complicated than previously assumed. Chapter 3 presents research on how power and phase of the neural signal relate to beat strength and beat location while controlling the stimulus-driven response. The results indicated a relationship between neural entrainment and beat strength, and also, between oscillatory phase and beat location. Chapter 4 presents research on the potential neural mechanisms of beat perception by examining neural activity during a silent immediately after rhythm perception for testing for ongoing, oscillatory activity. The results, although not statistically robust, suggest that entrained activity continues into silence, indicating a relationship between neural entrainment and beat perception. Chapter 5 presents a general discussion of Chapters 2-4 in the context of the existing literature, limitations, and broader interpretations of how these results relate to future directions in the field