Rhythmic Entrainment Echoes in Auditory Perception

Abstract

Rhythmic entrainment echoes, rhythmic brain responses that outlast rhythmic stimulation, can evidence endogenous neural oscillations entrained by the stimulus rhythm. We here tested for such echoes in auditory perception. Participants detected a pure tone target, presented at a variable delay after another pure tone that was rhythmically modulated in amplitude. In four experiments involving 154 participants, we tested (1) which stimulus rate produces the strongest entrainment echo and (2), inspired by audition's tonotopical organisation and findings in non-human primates, whether these are organized according to sound frequency. We found strongest entrainment echoes after 6-Hz and 8-Hz stimulation, respectively. Best moments for target detection (in or in anti-phase with the preceding rhythm) depended on whether sound frequencies of entraining and target stimuli matched, in line with a tonotopical organisation. However, for the same experimental condition, best moments were not always consistent across experiments. We provide a speculative explanation for these differences that relies on the notion that neural entrainment and repetition-related adaptation might exercise competing, opposite influences on perception. Together, we find rhythmic echoes in auditory perception that seem more complex than those predicted from initial theories of neural entrainment.

Neural tracking of continuous acoustics: properties, speech‐specificity and open questions

“…These neural ‘echoes’ are also seen in corresponding perceptual data, changing rhythmically after a rhythmic acoustic stimulus (Saberi & Hickok, 2023). This effect is observed for acoustic rhythms between 2 and 8 Hz (Farahbod et al, 2020; L'Hermite & Zoefel, 2023), suggesting an involvement of neural dynamics with similar constrained temporal flexibility as described above. A recent study suggested similar echoes produced by speech prosody at lower frequencies, confirming their relevance for speech processing (Lamekina & Meyer, 2023).…”

“…Brain imaging revealed that blood‐oxygen level dependent (BOLD) responses to amplitude modulated (AM) sounds are strongest if these are presented at 4–5 Hz (Giraud et al, 2000; Tanaka et al, 2000). Rhythmic AM sounds also give rise to rhythmic fluctuations in auditory sensitivity that outlast the stimulus, but only at rates between ~2 and 8 Hz (Farahbod et al, 2020; Hickok et al, 2015; L'Hermite & Zoefel, 2023). Non‐rhythmic acoustic stimuli, such as the onset of broadband noise, produce similar fluctuations in neural dynamics and auditory sensitivity in the delta–theta range, although the exact frequency remains unclear (~1–2 Hz in Kayser, 2019; ~5 Hz in Teng et al, 2018; ~6–8 Hz in Ho et al, 2017).…”

“…Importantly however, neural tracking has its limits: Neural dynamics fail to track the acoustic rhythm if it is too slow or too fast. These limits are defined by the system's eigenfrequency range: Most of the neural effects described in the previous section were observed for the delta–theta range but disappear if the stimulus is too fast or slow (Farahbod et al, 2020; Galambos et al, 1981; L'Hermite & Zoefel, 2023; Teng et al, 2017; Teng & Poeppel, 2020; Zaehle et al, 2010; but see Hertrich et al, 2012; Nourski et al, 2009, for neural responses that persist beyond the theta range). This suggests that neural dynamics are flexible but constrained by their eigenfrequency .…”