Detection of illicit phrasal movement in Huntington's disease

The role of the basal ganglia has been a longstanding issue in neural language models. Huntington's disease (HD) shows primary impairment in the striatum and has previously been shown to affect the processing of phrase-structural hierarchies that are built by phrasal movement (e.g. in passives). Here we asked patients with HD to judge the acceptability of sentences containing different types of illicit phrasal movement, which were contrasted with semantic violations involving no movement. A logistic mixed-effects regression showed that patients had a profound impairment in judging incorrect but not correct sentences across all types of illicit movement, while the semantic condition was also affected, but significantly less so. Adding neuropsychological variables to the model did not improve predictions. These results demonstrate a loss of cognitive control, worsening with disease progression, over phrase-structural hierarchies, which extends to forms of meaning built at sentential levels.