Selective impairment of adjective order constraints as overeager abstraction: An elaboration on Kemmerer etal. (2009)

Kemmerer, Tranel, and Zdanczyk (2009) reported patients who failed to discriminate between preferred and dispreferred orders of prenominal adjectives, yet were sensitive to the order of adjectives in relation to other parts of speech, and able to judge which of two adjectives was most similar to a cue adjective. The authors concluded that knowledge of the semantic constraints on prenominal adjective order can be impaired without an impairment of purely syntactic adjective order knowledge, or knowledge of semantic adjective classes. Using simulation studies, we demonstrate that the impairment of these patients can be characterized as overeager abstraction. Oversmoothing a similarity-based bigram language model with a similarity metric based on word co-occurrence distributions resulted in the same performance dissociation between tasks as reported for Kemmerer et al.’s selectively impaired patients. Additionally, the strength with which the patients preferred a specific adjective order for a given stimulus was predicted by the stimulus’ robustness to overeager abstraction. Our results provide a general cognitive account based on the online creation of temporary summary representations that is supported by current neurocognitive views on verbal cognition. This account lends a more insightful explanation for impairments of linguistic knowledge than an explanation relying solely on linguistic abstractions.