Аннотация:Recent studies show, that working memory functioning is impaired in people with stuttering (Bajaj, 2007; Kaganovich et al. 2010). However, there is still no certain neurophysiological explanation of this fact.
Participants in the study were 10 people with stuttering and 10 people without any speech impairments (8 men and 2 women in each subject group, mean age - 25,3±4,8 years old). We performed computer neuropsychological testing of visual working memory capacity. Subjects’ goal was to remember three simultaneously presented for 1000 ms visual stimuli and then find them in the same sequence among 16-20 similar stimuli after a 1200 ms delay. The test consisted of two series, which differed in stimuli type - complex geometric figures and words; the stimuli were based on A.R. Luria’s neuropsychological assessment materials. During the computer test event-related potentials were registered for the stimuli presentation. We compared the percentage of correct answers in the test between subject groups; event-related potentials were averaged for each part of the test and also compared between subject groups (the significance of the differences in ERP amplitudes was evaluated with Student’s t-test).
According to the results of the test, visual working memory capacity in stuttering is significantly lower in comparison to the control subjects for memorizing complex geometric figures, while memorizing words did not reveal any significant differences. ERP amplitudes differ significantly between subject groups on the 400-600 ms interval post-stimulus for the ‘geometric figures’ part of the test; for the second part of the test there were no significant differences in ERP amplitudes.
Furthermore, the coordinates of electrical activity dipole sources for 400-600 ms interval were calculated with BrainLoc 6.0 program (dipole coefficient > 0.95). For both parts of the test and both subject groups activation of orbitofrontal cortex and occipital lobe was revealed. However, the activation of orbitofrontal cortex in control subjects was stronger during more difficult part of the test than during the easier one, whereas in stuttering this activation was weaker (smaller amount of dipoles were revealed) regardless of the task difficulty. It can be speculated, that the resources of the central executive of working memory are limited in stuttering, which does not affect the performance in simple tasks but causes trouble during the difficult ones.