Modeling normal and impaired knowledge of semantic constraints on adjective order without explicit constraints

TitleModeling normal and impaired knowledge of semantic constraints on adjective order without explicit constraints
Publication TypeTalks
AuthorsVandekerckhove, B., Sandra D., & Daelemans W.
Place PresentedTalk given at the 20th Computational Linguistics In The Netherlands Conference, Utrecht, The Netherlands: Utrecht University
Year of Publication2010
Date Presented05/02/2010

Recent work in neurolinguistics (Kemmerer et al., 2009) reports six aphasics that are selectively impaired in their knowledge of the semantic constraints that govern pre-nominal adjective order. The patients failed a test in which they had to discriminate between preferred and dispreferred adjective arrangements (e.g. 'a big brown dog' vs. ?'a brown big dog'). At the same time, their performance in two other tests suggests that the patients' knowledge of the semantic categories to which these constraints apply (value, size, color, etc.) and of syntactic word order constraints (e.g. 'a big brown dog' vs. *'dog brown big a') are still intact.
We simulated the performance profile of these patients in the three tasks using a simple memory-based language processing model. The exemplar memory consists of (word, part-of-speech tag) tuples. Support for a target word sequence is given by the product of the probabilistic support for each part-of-speech in the sequence, conditional on the previous word token and its nearest neighbors. The distance between two exemplars is given by their Modified Value Difference.
By varying the number of neighbors taken into account for extrapolation in this model, we show how the aphasic patients can be characterized as 'overeager abstractors'. Their impairments might affect not so much abstract linguistic *knowledge* of explicit semantic constraints as the level of abstraction they employ over concrete exemplars during linguistic *processing*.

David Kemmerer; Daniel Tranel; & Cynthia Zdanczyk (2009). Knowledge of the semantic constraints on adjective order can be selectively impaired. Journal of Neurolinguistics 22, 91-108.