The neuromagnetic response to spoken sentences: Co-modulation of theta band amplitude and phase

Abstract

Speech elicits a phase-locked response in the auditory cortex that is dominated by theta (3–7 Hz) frequencies when observed via magnetoencephalography (MEG). This phase-locked response is potentially explained as new phase-locked activity superimposed on the ongoing theta oscillation or, alternatively, as phase-resetting of the ongoing oscillation. The conventional method used to distinguish between the two hypotheses is the comparison of post- to prestimulus amplitude for the phase-locked frequency across a set of trials. In theory, increased amplitude indicates the presence of additive activity, while unchanged amplitude points to phase-resetting. However, this interpretation may not be valid if the amplitude of ongoing background activity also changes following the stimulus. In this study, we employ a new approach that circumvents this problem. Specifically, we utilize a fine-grained time–frequency analysis of MEG channel data to examine the co-modulation of amplitude change and phase coherence in the post-stimulus theta-band response. If the phase-locked response is attributable solely to phase-resetting of the ongoing theta oscillation, then amplitude and phase coherence should be uncorrelated. In contrast, additive activity should produce a positive correlation. We find significant positive correlation not only during the onset response but also throughout the response period. In fact, transient increases in phase coherence are accompanied by transient increases in amplitude in accordance with a “signal plus background” model of the evoked response. The results support the hypothesis that the theta-band phase-locked response to attended speech observed using MEG is dominated by additive phase-locked activity.

Impaired auditory sampling in dyslexia: further evidence from combined fMRI and EEG

“…The reason is that our stimulus being conversational speech, there is no multiply-repeated stimulus that enables a well-defined spectro-temporal analyzis of the evoked response. We did not analyze the phase locking with the speech envelope either, because this would provide information about low frequencies (Howard and Poeppel, 2012), but not the gamma band, and we wanted to compare both frequency bands. Our analysis of correlations between the EEG power time course and the BOLD signal allowed us to estimate the degree to which activations in specific brain regions reflect cortical oscillations in given frequency bands.…”

The effects of selective attention and speech acoustics on neural speech-tracking in a multi-talker scene

“…Significant phase-locking to the sound envelope is also observed for unintelligible, time-inverted, or noise-vocoded speech as well as non-speech sounds (Lalor et al 2009; Howard and Poeppel 2012; Hämäläinen et al 2012; Peelle et al 2012; Wang et al 2012; Millman et al 2013; Steinschneider et al 2013; Ding et al 2014). Nonetheless, speech tracking is more robust for natural compared to noise-vocoded speech, in which the fine structure information is removed but the low-frequency temporal fluctuations contained in the speech envelope are preserved (Luo and Poeppel 2007; Howard and Poeppel 2010; Peelle et al 2012; Wild, Davis, et al 2012; Ding et al 2014).…”

Cortical oscillations and sensory predictions

“…This schematic compares the amplitude of an event-related response (N1, averaged across 10 trials) to unexpected (left panel) and expected (right panel) auditory stimuli. Because evoked responses [event-related potentials (ERPs) and event-related fields (ERFs)] are correlated with the phase-locking of (delta-theta) ongoing oscillations [84], their amplitude depends on the pre-stimulus phase distribution across trials. When a stimulus is anticipated (via the generation of cross-modal or rhythmic predictions), delta-theta phase-reset precedes stimulus onset, which gives rise to a response (ERPs, ERFs) to predicted stimuli of lower magnitude (right panel) relative to when phaselocking is only elicited by the stimulus onset (left panel).…”