Loudness adaptation under free-field listening

Previous reports [D. Fishken et al., J. Acoust. Soc. Am. Suppl. 1 61, S61 (1977); B. Scharf and T. J. Horton, J. Acoust. Soc. Am. Suppl. 1 63, SI6 (1978)] of loudness adaptation based upon the method of successive magnitude estimation showed that the loudness of a steady high-frequency tone presented through earphones decreases with duration provided the tone is within 20 to 30 dB of threshold. Tones below about 1 kHz and also white noise show much less adaptation. These measurements have been extended to freefield listening. Seated in an anechoic room with his head held steady. O faced a loudspeaker 3.7 m away. Tones were each presented for 3 min at l0 dB above threshold. Every 20 s a light came on for 2 s. The O assigned a number corresponding to the loudness of the tone during the 2-s interval. Results from 26 Os showed that the loudness of a 4-kHz tone decreased after 2 min by 60% and after 3 min by 76%. These values are similar to those measured previously for earphone listening. Tentative results at 8, 10, and 12 kHz suggest somewhat less adaptation at these higher frequencies. Why loudness adapts at low levels and high frequencies and not otherwise remains a mystery. [Research supported in part by NIH.]