Shared and distinct temporal representations of Chinese words across imaged, silent, and overt speech

How internal speech relates to overt speech remains a fundamental question in speech production: do different forms of speech preserve a common neural representation of the intended word, or does that representation change as speech becomes articulated? We used time-resolved electroencephalography to characterize representations of 10 Chinese words during imagined, silent, and overt speech. Word identity was reliably decodable in all three modes, but its temporal dynamics differed: imagined-speech representations peaked earlier and were less temporally stable, whereas silent and overt speech showed stronger and more sustained representations. Cross-mode decoding revealed word-discriminative information shared across all three mode pairs, with substantially stronger generalization between silent and overt speech. However, direct comparison of word-level representational geometry revealed robust correspondence only between silent and overt speech, indicating that transferable information across modes does not necessarily imply preservation of the broader relational structure among words. Representational similarity analyses further showed distinct visual-form, semantic, and phonetic dynamics across speech modes, with late visual-form and phonetic information contributing uniquely to the geometry shared by silent and overt speech. Controlling for time-matched surface electromyography preserved the overall silent-overt neural correspondence and within-mode phonetic representations, while eliminating the unique phonetic contribution to their shared geometry, suggesting that peripheral articulation accounts for part, but not all, of this common structure. Together, these findings show that imagined, silent, and overt speech share word representations at different levels and suggest that representational geometry and temporal stability are progressively reorganized as internal speech is translated into articulation.