Phonologic processing in adults who stutter: electrophysiological and behavioral evidence.

Event-related brain potentials (ERPs), judgment accuracy, and reaction times (RTs) were obtained for 11 adults who stutter and 11 normally fluent speakers as they performed a rhyme judgment task of visually presented word pairs. Half of the word pairs (i.e., prime and target) were phonologically and orthographically congruent across words. That is, the words looked orthographically similar and rhymed (e.g., thrown, own) or did not look similar and did not rhyme (e.g., cake, own). The phonologic and orthographic information across the remaining pairs was incongruent. That is, the words looked similar but did not rhyme (e.g., gown, own) or did not look similar but rhymed (e.g., cone, own). Adults who stutter and those who are normally fluent exhibited similar phonologic processing as indexed by ERPs, response accuracy, and RTs. However, longer RTs for adults who stutter indicated their greater sensitivity to the increased cognitive loads imposed by phonologic/orthographic incongruency. Also, unlike the normally fluent speakers, the adults who stutter exhibited a right hemisphere asymmetry in the rhyme judgment task, as indexed by the peak amplitude of the rhyming effect (difference wave) component. Overall, these findings do not support theories of the etiology of stuttering that posit a core phonologic-processing deficit. Rather we provide evidence that adults who stutter are more vulnerable to increased cognitive loads and display greater right hemisphere involvement in late cognitive processes.