A new empirical angle on the variability debate: Quantitative neurosyntactic analyses of a large data set from Broca’s Aphasia

• Published in: Brain and language 2006-02, Vol.96 (2), p.117-128
• Main Authors: Drai, Dan, Grodzinsky, Yosef
• Format: Article
• Language: English
• Subjects: Aphasia; Aphasia, Broca - diagnosis; Aphasia, Broca - physiopathology; Cerebral Cortex - physiopathology; Confidence interval; Confidence Intervals; Empirical Research; Humans; Language Disorders - diagnosis; Linguistic Performance; Linguistics - methods; Models, Biological; Patients; Quantitative analysis; Sentences; Severity of Illness Index; Statistical Analysis; Syntax; Variability; β-Distribution
• ISSN: 0093-934X; 1090-2155
• DOI: 10.1016/j.bandl.2004.10.016

Behavioral variation in Broca’s aphasia has been characterized as boundless, calling into question the validity of the syndrome-based schema and related diagnostic methods of acquired language disorders. More generally, this putative variability has cast serious doubts on the feasibility of localizing linguistic operations in cortex. We present a new approach to the quantitative analysis of deficient linguistic performance, and apply it to a large data set, constructed from the published literature: Comprehension data of 69 carefully selected Broca’s aphasic patients, tested on nearly 6000 stimulus sentences, were partitioned in different ways, and subjected to a series of analyses. While a certain amount of variability is indeed evident in the data, our quantitative analyses reveal a highly robust selective impairment pattern for the group: the patients’ ability to analyze syntactic movement is severely compromised, in line with the Trace-Deletion Hypothesis. Further analyses suggest that patients’ performance on no-movement sentence types exhibits less variation than on sentences that contain movement. We discuss the clinical and theoretical implications of our results.