PHYSIOLOGICAL AND TECHNOLOGICAL STUDIES ON THE AUDITORY SCENE ANALYSYS

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Human can recognize speeches even in noisy environments where noise masks speech sounds. This phenomenon is called 'cocktail party effect' or, by Bregman, 'auditory scene analysis' (1991). He suggested in his psychophysical studies that there are several auditory mechanisms underlying this effect such as temporal induction of sounds (restoration of original sounds in the periods masked by noise), segmentation, grouping and location of sounds. These mechanisms are not fully understood physiologically. The present study is aimed to investigate physiological mechanisms of auditory scene analysis in the auditory cortex and to make a neural model. Neural mechanisms of (1) temporal induction, (2) segmentation and grouping and (3) sound location were investigated in the guinea-pig auditory cortex using an optical imaging technique of neural activity and (4) a neural model of the auditory cortex and a noise-robust speech recognition model were studied. Responses to gap-inserted pure tone appea … More red at the onset of pre- and post-gap tone. The onset response to the post-gap tone was inhibited by insertion of noise, and this inhibition was stronger in the belt fields than in the AI. These results suggest that the inhibition of the onset detection after the noise is an important mechanism for auditory induction. The response in AI and the anterior belt field followed to the amplitude-modulated sounds (AM) at high modulation frequencies (fm) but the dorsocaudal field and the caudal belt field followed to AM at low fm, and the caudal belt field elicited the larger offset responses for the higher fm. These results show that the caudal belt fields have a longer time window to process sounds, suggesting that this field is more specialized to analyze complex sounds, and show that the offset response is involved in the sound-grouping mechanisms. The caudal belt fields were found to be more sensitive to the sound location than the AI. A neural model of the auditory cortex reproduced spatiotemporal neural activity of the AI. Less