A perceptual transition occurs when a person hears a repeated single word without a pause; this induces illusory changes of the word. We have been studying the conditions under which perceptual transitions occur. However, it is unclear whether the perceptual transition occurs in the peripheral or central auditory system. To elucidate this, we examined whether the perceptual transition occurred upstream or downstream of the superior olivary complex by dichotic presentation. Thirteen Japanese subjects were presented with six Japanese words. There were three types of presentation methods: (1) diotic presentation with ISI = 0, (2) diotic presentation with ISI = stimulus length, and (3) dichotic presentation to the left and right ears alternately. We measured the time (T) until the perceptual transition occurred. If T in (3) is close to T in (1), the perceptual transition is thought to occur upstream of the superior olivary complex, and if T in (3) is close to T in (2), it is thought to occur downstream of the superior olivary complex. The results in (3) were almost equal to those in (1), suggesting the possibility that it occurred upstream from the superior olivary complex.

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