On the Perception of Direction of Echo

The minimum time differences over which same two sounds coming from different directions in succession are heard separately in direction are obtained. When two clicks are used as stimuli, the second click is lateralized separately from the first click if the former lags more than 10 msec behind the latter and the second click is less than 20 dB smaller as compared with the first one. If an accessory click is inserted between these two clicks, the minimum time difference over which two stimuli are separately lateralized is longer than that in the case without an accessory click and its value amounts to 20∼30 msec. Such a minimum difference is 100∼200 msec in the case that the space between the first click and the second one is filled up with some stimuli. As one of the results, it is shown that this time difference is smaller for a sound containing more high-frequency component than for one containing less. Moreover, when two sounds with same duration are given to each ear with an interaural time difference, the minimum duration over which a sound image moves from side to center on the head is obtained. These data are discussed in regard to physiological facts.