Edwards B W, Viemeister N F
Department of Psychology, University of Minnesota, Minneapolis 55455.
J Acoust Soc Am. 1994 Aug;96(2 Pt 1):733-40. doi: 10.1121/1.411440.
The encoding mechanisms for amplitude modulation (AM) and frequency modulation (FM) were investigated using AM-FM discrimination tasks. In the first experiment, AM and FM were set at equally detectable levels within a trial, and discrimination thresholds were obtained adaptively in a 3IFC task. Here, AM-FM discrimination thresholds were considerably larger than both AM and FM detection thresholds. This is consistent with an encoding system whereby AM and FM are partially encoded by the same mechanism. In the second experiment, performance on AM-FM discrimination is measured with a fixed-level procedure. Psychometric functions obtained for a constant modulation depth of AM were nonmonotonic with FMs modulation index beta and each displayed a single minimum. The nonmonotonic nature of the functions is consistent with a model in which FM is encoded primarily with the same mechanism that encodes AM but also with a second mechanism, probably related to changes in instantaneous frequency, that is independent of the mechanism that extracts AM. The fact that minima in the discrimination psychometric functions increase from d' = 0 as beta increases indicates that the information encoded by the second mechanism becomes more detectable with increasing beta.
使用调幅（AM）和调频（FM）辨别任务研究了调幅和调频的编码机制。在第一个实验中，在一次试验中，将调幅和调频设置为同等可检测水平，并在三间隔迫选（3IFC）任务中自适应地获得辨别阈值。在此，调幅 - 调频辨别阈值远大于调幅和调频检测阈值。这与一种编码系统一致，即调幅和调频部分由相同机制编码。在第二个实验中，用固定水平程序测量调幅 - 调频辨别性能。对于调幅的恒定调制深度获得的心理测量函数随调频调制指数β呈非单调变化，且每个函数都显示出一个单一最小值。这些函数的非单调性质与一个模型一致，在该模型中，调频主要由与编码调幅相同的机制编码，但也由第二种机制编码，可能与瞬时频率的变化有关，该机制独立于提取调幅的机制。辨别心理测量函数中的最小值随着β增加从d' = 0开始增大这一事实表明，随着β增加，第二种机制编码的信息变得更易检测。
