Summation priming in aphasia: evidence for alterations in semantic integration and activation.

The present study used a lexical decision paradigm to study the summation of priming effects in normal and aphasic participants. The amount of priming produced by pairs of definitionally converging associative words was compared to the amount of priming produced by pairs of single associative words and non-words in two experiments in which the ISI between primes and targets varied from 200 ms (Experiment 1) to 600 ms (Experiment 2). Control subjects showed a pattern of additive summation priming at the short ISI and overadditive summation priming at the longer ISI. Broca's aphasics showed overadditive priming at the short ISI and no significant priming at the longer ISI; Wernicke's aphasics showed no significant priming at the short ISI and additive priming at the longer ISI. These results suggest that aphasics differ from normals in their ability to integrate the activation derived from multiple linguistic associations and may provide an account of some of the clinical phenomenology of these patients.