The purpose of the present experiment was to examine developmentally the effects of frequencies (4 and 10sec) of intermittent sounds given during the standard time on the reproduced time which was estimated by the method of reproduction. The buzzer was intermittently given for 0.1sec at the intervals of 0.3, 0.5, 0.6, 0.75 and 1.2sec in Experiment 1, and at the intervals of 0.15, 0.2, 0.4, 0.75 and 2.0sec in Experiment 2. These five conditions of buzzer frequencies were at random presented four times respectively for each subject. Besides the pulse rate in the condition of sitting still, the tempo of metronome which was accepted most comfortably and the pace of tapping at his own preferred speed were measured for each subject and the relation of these tempos to the estimated time was examined. The subjects were as shown in Table 1.<br>The results were as follows:<br>Generally the higher the frequency of sounds was, in other words, the shorter the sound interval was, the longer was the estimated time. This finding conforms to the theory of the number of perceived changes stated by Fraisse. And the younger the subjects were, the stronger were the effects of sounds. At the intervals centering around 0.7sec, however, the relation of the sound frequency to the estimated time was not so simple as above mentioned, and the ranges of such frequencies were wider for the older subjects. Besides it was not observed in the older subjects that the estimated time tended to prolong according to the frequency for such high frequencies of sound as 0.2sec and/or 0.15sec (see Fig. 1 & Fig. 2).<br>2. The smallest mean deviation among the various conditions of sound frequency was obtained for each subject chiefly at the intervals near 0.7sec in all age-groups and it was also observed that the rates of the subjects' pulses and their preferred tempos of metronome and tapping center around the above frequency (see Fig. 2, Fig. 4 & Table 4).<br>These results indicate that these tempos may be the bases of time estimation, so both the mean deviations and the effects of sounds were small for the sound frequencies near 0.7sec And because these tempos might have been firmly established in the adults as the basis of time estimation, the range of the intervals of sounds with such slight effects on time estimation as mentioned in 1 was wide.<br>3. The reproduced times in those young children who preferred fast tempos of metronome were long, and those young children whose reproduced times were prolonged along with the higher frequencies of sound generally preferred fast tempos of metronome. This relation became looser with age development and even reversal in the adults (see Table 6, Table 7, Table 11 & Table 12).