Selective Disruption of Linearization in Non-Speaking Autism: A Cortico-Striatal Account and a Direct Test of the Comprehension–Expression Dissociation

Non-speaking autistic individuals (nsASD) frequently present with a receptive–expressive discrepancy: a subgroup comprehends hierarchically structured language while producing little or no ordered multi-symbol output, across speech, gesture, and augmentative and alternative communication (AAC) alike. Whether hierarchical comprehension is genuinely preserved in this subgroup has, however, remained difficult to establish, because every standard measure of comprehension requires some form of ordered response — confounding the very output channel whose failure defines the profile. The question has thus stayed open not because evidence weighs against preserved comprehension, but because the methods needed to test it directly have been unavailable. To address this measurement gap, the present account takes two complementary approaches. It proposes that the profile reflects a selective disruption of linearization — the interface operation mapping hierarchical structure onto one-dimensional temporal output — at the implementation level of cortico-striatal sequencing circuits, leaving the generation of hierarchical structure intact. On this basis it introduces the Hierarchy-Dependent Comprehension Task (HDCT), a paradigm designed to isolate hierarchical comprehension from output load and to test, rather than presuppose, the preserved-comprehension claim. A three-stage model of externalization situates the account and generates testable predictions, including a structural comparison with Broca's aphasia.