Selective impairment of knowledge underlying prenominal adjective order: evidence for the autonomy of grammatical semantics

English speakers have strong preferences for the order in which adjectives can occur before a noun - e.g. big brown dog vs. *brown big dog. These ordering preferences are based on a restricted set of semantic features which include fairly abstract functional distinctions like descriptive vs. classifying as well as information about adjective categories like size vs. color. Other perceptual and conceptual features of adjective meaning - e.g. particular colors like brown vs. black -do not influence the syntactic behavior of the words. According to the grammatically relevant semantic subsystem hypothesis proposed by Pinker [Pinker S. Learnability and Cognition. Cambridge, MA: MIT Press, 1989], it is reasonable to suppose that the features of adjective meaning that constrain their linear order reside at a different level of mental representation than the features that are invisible to syntax. If this is true, then it is possible that the two components of meaning could be impaired independently of each other by brain damage. This paper reports a series of experiments that confirmed this prediction. Six of 16 brain-damaged subjects failed a test that assessed their knowledge of the semantic principles that determine prenominal adjective order. However, all of the subjects-performed within normal limits on a second test that assessed their knowledge of the grammatically irrelevant perceptual and conceptual features of the same adjectives that were used in the first test. In addition, all of the subjects performed well on a third test that assessed their knowledge of the basic syntactic structure of English noun phrases (NPs). Taken together, these results suggest that the brain-damaged subjects who failed the first test have impaired knowledge of the grammatically relevant semantic features that influence prenominal adjective order; in contrast, they have well-preserved knowledge of grammatically irrelevant aspects of adjective meaning and of basic elements of NP syntax. This study therefore provides support for the view that there is an independent level of representation in the mind/brain for grammatical semantics. (C) 2000 Elsevier Science Ltd. All rights reserved.