Moody D B, May B, Cole D M, Stebbins W C
Exp Biol. 1986;45(3):219-32.
Frequency modulation is a common feature of acoustic communication signals, including both human speech and many animal calls. In this study, linear frequency upsweeps were used as simple abstractions of the modulations found in communication signals. Macaque monkeys were trained using positive reinforcement operant conditioning procedures to respond when an ongoing repetitive acoustic signal changed from unmodulated (pure tone) to modulated (sweep). Thresholds for detecting modulation were determined using the psychophysical method of constant stimuli. In the first experiment, it was shown that the monkeys were most sensitive to modulation around a center frequency of 500 Hz. Subsequent experiments were carried out at that frequency, and varied stimulus duration and the frequency relationship between standard and comparison stimuli. The results of these studies indicated that subjects were responding primarily to discrete frequency cues rather than to the presence of modulation. When a premium was placed on attending to modulation by presenting discrete shifts between successive unmodulated stimuli thereby making such shifts an unreliable indicator of the presence of modulation, subjects continued to respond to the presence of the discrete shifts. These results are taken as evidence that the auditory system may deal with frequency modulation near threshold by recoding it as a discrete frequency percept.
频率调制是声学通信信号的一个常见特征，包括人类语音和许多动物叫声。在本研究中，线性频率上升扫描被用作通信信号中发现的调制的简单抽象。猕猴通过正强化操作性条件反射程序进行训练，以便在持续的重复声学信号从未调制（纯音）变为调制（扫描）时做出反应。使用恒定刺激的心理物理学方法确定检测调制的阈值。在第一个实验中，结果表明猴子对中心频率为500Hz左右的调制最为敏感。随后的实验在该频率下进行，并改变了刺激持续时间以及标准刺激和比较刺激之间的频率关系。这些研究结果表明，受试者主要对离散频率线索做出反应，而不是对调制的存在做出反应。当通过在连续的未调制刺激之间呈现离散变化从而使这种变化成为调制存在的不可靠指标来强调关注调制时，受试者继续对离散变化的存在做出反应。这些结果被视为证据，表明听觉系统可能通过将频率调制重新编码为离散频率感知来处理接近阈值的频率调制。
