EN
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.