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Distinct Theta Synchrony across Speech Modes: Perceived, Spoken, Whispered, and Imagined

Jung-Sun Lee, Ha-Na Jo, Eunyeong Ko

TL;DR

This work addresses how theta-band ($4$-$8$ Hz) neural synchrony varies across perceived, overt, whispered, and imagined speech to inform multi-mode BCIs. It combines high-density EEG with PLV, PLI, and coherence analyses to map region-wise connectivity patterns. Findings show overt and whispered modes engage broad frontotemporal networks, perceived speech relies on posterior-temporal areas, and imagined speech exhibits a more localized frontal-central pattern. These insights highlight both shared and distinct neural mechanisms and support the development of mode-aware decoding strategies for naturalistic speech interfaces.

Abstract

Human speech production encompasses multiple modes such as perceived, overt, whispered, and imagined, each reflecting distinct neural mechanisms. Among these, theta-band synchrony has been closely associated with language processing, attentional control, and inner speech. However, previous studies have largely focused on a single mode, such as overt speech, and have rarely conducted an integrated comparison of theta synchrony across different speech modes. In this study, we analyzed differences in theta-band neural synchrony across speech modes based on connectivity metrics, focusing on region-wise variations. The results revealed that overt and whispered speech exhibited broader and stronger frontotemporal synchrony, reflecting active motor-phonological coupling during overt articulation, whereas perceived speech showed dominant posterior and temporal synchrony patterns, consistent with auditory perception and comprehension processes. In contrast, imagined speech demonstrated a more spatially confined but internally coherent synchronization pattern, primarily involving frontal and supplementary motor regions. These findings indicate that the extent and spatial distribution of theta synchrony differ substantially across modes, with overt articulation engaging widespread cortical interactions, whispered speech showing intermediate engagement, and perception relying predominantly on temporoparietal networks. Therefore, this study aims to elucidate the differences in theta-band neural synchrony across various speech modes, thereby uncovering both the shared and distinct neural dynamics underlying language perception and imagined speech.

Distinct Theta Synchrony across Speech Modes: Perceived, Spoken, Whispered, and Imagined

TL;DR

This work addresses how theta-band (- Hz) neural synchrony varies across perceived, overt, whispered, and imagined speech to inform multi-mode BCIs. It combines high-density EEG with PLV, PLI, and coherence analyses to map region-wise connectivity patterns. Findings show overt and whispered modes engage broad frontotemporal networks, perceived speech relies on posterior-temporal areas, and imagined speech exhibits a more localized frontal-central pattern. These insights highlight both shared and distinct neural mechanisms and support the development of mode-aware decoding strategies for naturalistic speech interfaces.

Abstract

Human speech production encompasses multiple modes such as perceived, overt, whispered, and imagined, each reflecting distinct neural mechanisms. Among these, theta-band synchrony has been closely associated with language processing, attentional control, and inner speech. However, previous studies have largely focused on a single mode, such as overt speech, and have rarely conducted an integrated comparison of theta synchrony across different speech modes. In this study, we analyzed differences in theta-band neural synchrony across speech modes based on connectivity metrics, focusing on region-wise variations. The results revealed that overt and whispered speech exhibited broader and stronger frontotemporal synchrony, reflecting active motor-phonological coupling during overt articulation, whereas perceived speech showed dominant posterior and temporal synchrony patterns, consistent with auditory perception and comprehension processes. In contrast, imagined speech demonstrated a more spatially confined but internally coherent synchronization pattern, primarily involving frontal and supplementary motor regions. These findings indicate that the extent and spatial distribution of theta synchrony differ substantially across modes, with overt articulation engaging widespread cortical interactions, whispered speech showing intermediate engagement, and perception relying predominantly on temporoparietal networks. Therefore, this study aims to elucidate the differences in theta-band neural synchrony across various speech modes, thereby uncovering both the shared and distinct neural dynamics underlying language perception and imagined speech.

Paper Structure

This paper contains 7 sections, 3 equations, 2 figures, 1 table.

Table of Contents

  1. INTRODUCTION
  2. MATERIALS AND METHODS
  3. Dataset Description
  4. Signal Preprocessing
  5. Functional Connectivity
  6. RESULTS AND DISCUSSION
  7. CONCLUSIONS

Figures (2)

  • Figure 1: Theta-band PLV-based functional connectivity across four speech modes: (a) perceived, (b) overt, (c) whispered, and (d) imagined speech. Each circular graph represents inter-regional phase synchrony derived from the theta band. Node colors indicate cortical regions (frontal, central, temporal, parietal, and occipital), as illustrated in the accompanying legend.
  • Figure 2: Theta-band coherence-based functional connectivity across four speech modes: (a) perceived, (b) overt, (c) whispered, and (d) imagined speech. Each circular graph represents inter-regional phase synchrony derived from the theta band. Node colors indicate cortical regions (frontal, Ceftral, temporal, parietal, and occipital), as illustrated in the accompanying legend.