| Summary: | 碩士 === 國立陽明大學 === 腦科學研究所 === 97 === Background: Detection of sound duration is important for language perception. Duration change has been reflected by mismatch negativity (MMN) or its magnetic counterpart (MMNm) in oddball paradigms. MMN-like responses to short-duration sound were also found in an equiprobable-paradigm. It is thus hypothesized that there exists a preferential reactivity of human brains to duration shortening. The present study aimed to study how our brains differentially react to duration-varying tones based on neuromagnetic as well as behavioral measures. Materials and Methods: In Experiment 1, magnetoencephalographic responses were recorded in ten subjects to 25~125ms equiprobable paradigm (25-50-75-100-125 ms tones), 50~150ms equiprobable paradigm (50-75-100-125-150 ms tones), and single-tone paradigms of 25-ms or 50-ms duration. In Experiment 2, the subjects performed behavioral tasks after recognizing an assigned target sound in an individual equiprobable paradigm. In Experiment 3, the effect of deviance magnitude of the shortest tone within an equiprobable paradigm on neuromagnetic responses was evaluated in ten subjects. Results: MMNm-like activities, called sub-standard MMNm, were clearly elicited by the shortest tone in equiprobable conditions. For the same stimulus (25ms or 50ms tone), the generator of the sub-standard MMNm was anterior to that of the N100m. Higher correct response rates and lower error response rates were found while discriminating the shortest tone compared with discriminating longer tones. Moreover, sub-standard MMNm amplitude tended to increase with the increment of deviance magnitude of the shortest tone.
Conclusions: In conclusion, human brains are sensitive particularly to the shortest tone as revealed by the characteristic of sub-standard MMNm and behavioral performance.
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