Moore B C, Sek A
Department of Experimental Psychology, University of Cambridge, England.
J Acoust Soc Am. 1995 Apr;97(4):2468-78. doi: 10.1121/1.411967.
Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d' of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d' up to about 2), some subjects discriminated the type of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of of phase-locking information depends on the time that the stimuli spend at frequency extremes.
最初，使用二选一强制选择（2AFC）任务测量心理测量函数，以检测调幅（AM）或调频（FM）。载波频率为125、1000和6000赫兹，调制率为2、5和10赫兹。对于两个较低的载波频率，调频检测在最低调制率时往往最佳，而调幅检测在最高调制率时最佳。对于6000赫兹的载波，调幅和调频检测在最低调制率时往往最差。然后，选择可同等检测到的调幅和调频值对，并再次在2AFC任务中测量心理测量函数，以区分调幅和调频。对于125和1000赫兹的载波频率，在最高调制率（10赫兹）时，区分调幅和调频的能力总是最差；在这个速率下，当调制的可检测性相对较低（d'为1.16及以下）时，一些受试者基本上无法区分调幅和调频。对于2赫兹的调制率，当调制的可检测性适中（d'高达约2）时，一些受试者能够区分调制类型，但调制类型的辨别能力在最高调制率时仍有变差的趋势。不同受试者之间调制率有所不同，但在最高调制率时调制类型的辨别能力仍有变差的趋势。有人认为，对于所有载波频率，10赫兹调制率下的调频检测主要基于激发水平的变化。对于2赫兹的调制率以及两个最低的载波频率，一种可能基于锁相的额外机制可能在调频的检测和辨别中起作用。这种机制在高于约5赫兹的调制率下可能无效，因为刺激在频率极值处花费的时间不足。为了验证这一点，使用每秒五个周期的准梯形调制以及250、1000和6000赫兹的载波，测量调频和调幅检测的心理测量函数。与5赫兹正弦调制相比，这提高了性能，并且仅对于两个较低的载波频率，调频检测的性能提升明显大于调幅检测。这与使用锁相信息取决于刺激在频率极值处花费的时间这一观点一致。
