Sentence comprehension disorders in aphasia: The concept of chance performance revisited

Abstract

Background: In behavioural tests of sentence comprehension in aphasia, correct and incorrect responses are often randomly distributed. Such a pattern of chance performance is a typical trait of Broca's aphasia, but can be found in other aphasic syndromes as well. Many researchers have argued that chance behaviour is the result of a guessing strategy, which is adopted in the face of a syntactic breakdown in sentence processing.

Aims: Capitalising on new evidence from recent studies investigating online sentence comprehension in aphasia using the visual world paradigm, the aim of this paper is to review the concept of chance performance as a reflection of a syntactic impairment in sentence processing and to re-examine the conventional interpretation of chance performance as a guessing behaviour.

Main Contribution: Based on a review of recent evidence from visual world paradigm studies, we argue that the assumption of chance performance equalling guessing is not necessarily compatible with actual real-time parsing procedures in people with aphasia. We propose a reinterpretation of the concept of chance performance by assuming that there are two distinct processing mechanisms underlying sentence comprehension in aphasia. Correct responses are always the result of normal-like parsing mechanisms, even in those cases where the overall performance pattern is at chance. Incorrect responses, on the other hand, are the result of intermittent deficiencies of the parser. Hence the random guessing behaviour that persons with aphasia often display does not necessarily reflect a syntactic breakdown in sentence comprehension and a random selection between alternatives. Instead it should be regarded as a result of temporal deficient parsing procedures in otherwise normal-like comprehension routines.

Conclusion: Our conclusion is that the consideration of behavioural offline data alone may not be sufficient to interpret a performance in language tests and subsequently draw theoretical conclusions about language impairments. Rather it is important to call on additional data from online studies that look at language processing in real time in order to gain a comprehensive picture about syntactic comprehension abilities of people with aphasia and possible underlying deficits.

Keywords:

• Sentence comprehension in aphasia
• Chance performance
• Visual world paradigm
• Eye tracking
• Online sentence processing.

Notes

This review was written in the framework of a research project funded by the German Science Foundation (DFG, VA 482/4-1).

¹The TDH is based on transformational theories of grammar (e.g., Chomsky, 1986). These assume that non-canonical structures are derived from canonical sentences by moving the object from its base position adjacent to the verb and after the subject to the sentence initial position leaving behind a gap filled with a trace t (or copy).

²According to the VP-internal subject hypothesis (Koopman & Sportiche, 1991) the subject is moved from its position inside the VP to a higher node in the syntactic tree in the derivation of a sentence.

³In addition to wh-questions, Dickey and colleagues also used yes-no questions and object clefts as comprehension probes. For the sake of simplicity we only report the results that are important for the purpose of this review.