Consequences of an inhibition deficit for word production and comprehension: evidence from the semantic blocking paradigm.

We investigated the semantic blocking effect in picture naming and word-picture matching for two nonfluent aphasic patients who show evidence of a deficit in inhibiting verbal representations (M.L. and B.Q), one fluent aphasic patient (K.V.), and neurologically intact control participants. In two picture-naming tasks (Experiments 1A and 1B), M.L. and B.Q, relative to controls, showed a greatly exaggerated semantic blocking effect in naming latencies that increased dramatically across repeated presentations. On two corresponding word-picture matching tasks (Experiments 2A and 2B), both also showed an increasing semantic blocking effect, though the effects were not as large nor as consistent as those in naming. The fluent patient, K.V., showed a pattern like controls on both tasks. On an associated word-picture matching task, both M.L. and B.Q showed results paralleling those of controls. The contrast between the production and comprehension patterns for M.L. and B.Q. supports the conclusion that their exaggerated blocking effect in production arises during lexical rather than semantic selection. We postulate that M.L.'s (and potentially B.Q's) production effect is due to difficulties in postselection inhibition, which results in overactivation of lexical representations. This overactivation is likely to be one source of their nonfluency in spontaneous speech.