脳幹の複合音処理機能 : 家兎下丘ニューロンの母音様刺激音に対する応答

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Responses of the inferior colliculus neurons to complex tones were recorded with microelectrode technique in anesthetized rabbits. Complex tones for stimuli were composed of two pure tones with frequencies and sound pressure ratios, corresponding to center frequencies of the first and second formants of eight American English vowels. A complex tone and two pure tones which composed this tone were used as one group. The data were obtained from 60 neurons and studied in the form of PST (post-stimulus time) histogram. PST histograms of responses to complex tones were scrutinizingly compared with those for component tones presented singly and classified into the following 6 types: 1) Responses that represented patterns of PST histograms for the pure tones corresponding to the first foamants. About one-half of the responses belonged to this type. 2) Responses that represented patterns for pure tones corresponding to the second formants. 3) Responses that exhibited a reduction of the discharge rate in comparison with the responses to each component tones presented singly. 4) Responses that exhibited phase-locked discharge and combination tone response. 5) Responses that exhibited no discharge to any three stimuli. 6) Responses that had a higher discharge rate than the summation of the responses to both component tones or represented the different discharge patterns from component tones. A small number of neurons showed these responses. The last type of responses can not be explained by adaptation and/or suppression between two tones which have been observed in the level up to the cochlear nucleus. It may be assumed that the neurons which showed these responses act as neuronal detector of complex tone, because they were remarkably sensitive to those particular stimuli. The results of this study indicate that there already exists the processing function of speech signals concerning detection and analysis of different phonemes in the auditory pathway up to the inferior colliculus.
社団法人日本耳鼻咽喉科学会の論文

脳幹の複合音処理機能 : 家兎下丘ニューロンの母音様刺激音に対する応答

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