Independent effects of imageability and grammatical class in synonym judgement in aphasia

Background: The grammatical class effect in aphasia, i.e. dissociated processing of words according to their respective grammatical class, has been attributed to either grammatical, lexical or semantic (i.e., imageability) deficits. This study explores the hypotheses of impaired semantic treatment as the source of the grammatical class effect in aphasia. Method: A synonym judgement task that includes nouns and verbs of high and low imageability has been administered to 30 Spanish-speaking patients suffering from receptive or productive aphasia and 30 controls. Results: Normal controls performed significantly better than aphasic patients. Although globally the productive aphasics performed significantly better than the receptive aphasics, grammatical class (nouns better than verbs) and imageability (high imageability better than low imageability) affected performance in both subgroups. No significant interaction emerged between these two factors. Conclusion: The results suggest that the grammatical class effect may emerge from semantic impairment and that it is at least partially-independent of the imageability of words.