Sign language narrative reveals universal and modality-specific features of cortical timescale hierarchy.

Human languages are unique in their capacity to tell stories. Prior neuroimaging studies show that spoken language narrative comprehension engages a neural time-scale hierarchy, from words and sentences to narratives. Sign languages share core features with spoken languages but also have modality-specific elements such as use of hands, face and spatial position to convey meaning and mark grammar. Here, we use naturalistic fMRI to examine which aspects of the language hierarchy are speech-specific versus modality-general. Native signers (n = 20) watched a 20-minute Polish Sign Language interpretation of The Fall of the House of Usher and its progressively scrambled versions during fMRI. We show that signed narratives synchronize hierarchical neural networks, revealing a modality-invariant dissociation between frontotemporal regions, which track sentence-level structure, and the Default Mode Network tracking plot. We identify two signatures not previously reported for speech: the superior parietal cortex synchronizes at long discourse timescales, while the ventral occipital cortex responds to word- and sentence-level processing. These results reveal both universal and potentially modality-specific aspects of language neurobiology.