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The study concerns the effect of task difficulty on perception of temporal order (TO) for auditory stimuli presented in rapid succession. The measurement comprises auditory mismatch negativity (MMN), i.e., a negative potential with latency from 100 to 250 ms, induced by preattentive changes during auditory stimulation (Näätänen et al. 1978). Fifteen healthy volunteers, aged 21-29 years, participated in this study. The stimuli were two white noises of 10-ms (short) and 50-ms (long) durations. Within each pair noises were separated by a silent gap of 160, 60 or 10 ms, corresponding to three different levels of TO task difficulty, specifically: “easy”, “moderate” or “difficult”. An auditory oddball paradigm was used, thus a standard and deviant stimuli were presented. In half of the subjects deviants were short-long noises and in the other half long-short noises. Standards were long-short or long-short sequences, respectively. The subject’s task was to watch a silent movie on a computer screen without paying any attention to these auditory stimuli. The stimuli were presented in 9 blocks (3 blocks per each difficulty level). Each of them contained 200 stimuli (20% deviants and 80% standards). Both standard and deviant stimuli were presented in random order. The EEG signal was registered from 64 electrodes, using Brain Products EEG with reference to all averaged electrodes. We expect in ‘easy’ task the MMN with higher amplitudes and/or shorter latencies, than in more difficult tasks, corresponding to gaps of 60 ms, or 10 ms.
Temporal information processing (TIP) is a well known neural process that underlies many aspects of human cognition, e.g., speech comprehension and speech production. The specific disorders of these language functions result from left hemispheric brain damage. A lot of literature data, as well as earlier experiments performed in our Laboratory have indicated that specific temporal training improves both TIP and auditory comprehension. The aim of this study was to test whether such a training in aphasic patients influences selectively speech reception, or also speech production. We compared performance of ten aphasic subjects before and after the training. Patients attended 16 training sessions (3 sessions a week, 45 minutes each). The training task was to indicate the temporal-order of two sounds presented to both ears in rapid succession. The task difficulty was adjusted adaptively, according to subject’s performance. Before and after the training both TIP abilities (temporal-order threshold measuring for two monaurally presented clicks) and language skills were tested. Language tests comprised global auditory comprehension and phonemic hearing on word and sentence levels, moreover, naming and verbal fluency. The preliminary results showed that our temporal training improved both auditory speech comprehension and speech production. These results indicate that temporal mechanisms underlying both receptive and expressive language functions can be ameliorated by the specific temporal training in milliseconds time domain. Supported by 507/1/N-DFG/2009/0.
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