Impaired comprehension of reversible sentences is widely observed in aphasia. Reversible sentences (e.g., The cat chased the dog) cannot be interpreted accurately without attention to word order and other syntactic devices, whereas the sole plausible interpretation of nonreversible sentences (e.g., The cat drank the milk) can be derived from content words via semantic or pragmatic inferencing. Impaired comprehension of reversible sentences, along with relatively intact comprehension of single words and nonreversible sentences, most frequently co-occurs with Broca's aphasia but is also observed in other forms of aphasia (Caramazza and Zurif, 1976; Martin and Blossom-Stach, 1986; Caramazza and Micelli, 1991). This comprehension pattern, termed asyntactic comprehension, has been studied intensively as evidence about the syntactic abilities of aphasic listeners.

Accounts of asyntactic comprehension differ in two dimensions. The first is competence versus performance: Does the failure to interpret reversible sentences correctly derive from a loss of linguistic knowledge or language-processing ability, or does this failure stem from performance factors such as resource limitations? The second dimension is parsing versus mapping: Does asyntactic comprehension derive from a failure to parse or from a failure to map an accurate parse onto a semantic representation?