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The present study was designed to investigate the context effect on loudness judgment. Exp. 1 was done in just the same way as Garner did in 1954. Ss were asked to make half loudness judgment. The variable stimulus series were 55-65dB, 65-75dB and 75-85dB 1000Hz pure tone, each with 90dB standard tone. 5 Ss for each series. Here the paint of half loudness of the standard was almost the midpoint of each stimulus series. This is the same result as Garners, and shows that half loudness judgment depends on the stimulus context (Table 1). In Exp. 2, the noise in the electric car was used as a stimulus and stimulus series were 50-75dB, 60-85dB, 70-95dB and 45-95dB. 5 Ss for each series were instructed to judge absolutely the loudness using 7 categories. A clear context effect was found as shown in Fig. 1. The results of Exp. 1 and 2 indicate that there evidently exists the context effect on loudness judgment.The question is why such context effect appears. Helson says in his Adaptation-level theory that the judgments are made on the basis of sensory character and that the shifts in judgment reflect the change in sensation. On the other hand, Stevens insists that the context effect appears as a result of semantic limitation of verbal reports. Therefore in Exp. 3 reaction time was used as an index of loudness. White noise (w. n.) and band noise (b. n.; center frequency 4000Hz) were used as stimuli and Ss were instructed to respond only to white noise by releasing the key as soon as they heard the noise. The stimulus series were 60-80dB w. n. & 50-70dB b. n., 70-90dB w. n. & 60-80dB b. n., 80-100dB w. n. & 70-90dB b. n. and 60-100dB w. n. & 50-90dB b. n. 5 Ss for each series. The result showed a clear context effect between sound pressure level and reaction time as shown in Fig. 3 and Table 2.It is quite remarkable that there exists the context effect in the experiment using reaction time which is quite free from the semantic effect or Ss' intentional modification. Although reaction time cannot be said to represent the real value of sensation, and there is a possibility that reaction time may be influenced by motor effect, this result may be said to be a noteworthy one since it suggests that the context effect is not to be entirely attributed to the semantic effect as Stevens insists, but may reflect the change in sensory character.
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音の大きさ判断における文脈効果

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