Canévet G, Scharf B
Laboratoire de Mécanique et d'Acoustique, CNRS, Marseille, France.
J Acoust Soc Am. 1990 Nov;88(5):2136-42. doi: 10.1121/1.400110.
A sound at a low level is heard as much softer after having decreased continuously from higher levels than if presented after a period of silence at that same low level. Canévet [Acustica 61, 256-264 (1986)] demonstrated this phenomenon for a tone that (1) decreased from 65 to 20 dB in 180 s; he also presented a tone that (2) increased from 20 dB, or (3) was presented as pairs of bursts at various levels in random order. Below about 40 dB, loudness changed most rapidly in the decreasing condition so that, at 20 dB, the tone was judged ten times softer than in conditions (2) and (3). In the present experiments, magnitude estimation was used to examine the possible role of judgmental biases and adaptation in this rapid loudness decline, which we call decruitment. Results show that decruitment did not come about because subjects made many successive loudness judgments; loudness declined as much when a tone was judged only twice, at the beginning and end of its 180-s decrease. In contrast, interrupting the decreasing tone so that it was heard only at 70 dB and 160 s later at 30 dB greatly diminished the decruitment. Similarly, pairs of 500-ms tone bursts presented at successively lower levels instead of continously decreasing did not show decruitment, suggesting that sequential biases are irrelevant. The likely cause of decruitment is sensory adaptation.
与在相同低水平的一段沉默后呈现相比，从较高水平持续下降后的低水平声音听起来要柔和得多。卡内韦[《声学学报》61卷，256 - 264页(1986年)]针对一种音调演示了这一现象，该音调(1)在180秒内从65分贝降至20分贝；他还呈现了一种从20分贝开始上升的音调(2)，或者(3)以随机顺序在不同水平呈现为成对的脉冲串。在大约40分贝以下，响度在下降条件下变化最快，以至于在20分贝时，该音调被判定比条件(2)和(3)中的音调柔和十倍。在本实验中，采用量级估计法来检验判断偏差和适应在这种我们称为响度递减的快速响度下降中可能起的作用。结果表明，响度递减并非因为受试者进行了多次连续的响度判断；当一个音调在其180秒下降过程的开始和结束时仅被判断两次时，响度下降幅度相同。相比之下，中断下降的音调，使其仅在70分贝时被听到，160秒后在30分贝时被听到，大大减弱了响度递减。同样，以连续降低的水平而非连续下降的方式呈现成对的500毫秒音调脉冲串时，未出现响度递减，这表明顺序偏差无关紧要。响度递减的可能原因是感觉适应。
