Medizinische Physik, Universität Oldenburg, 26111 Oldenburg, Germany.
J Acoust Soc Am. 2012 Jan;131(1):398-408. doi: 10.1121/1.3662078.
Second-order amplitude modulation is a relatively slow variation of the modulation depth of a first-order amplitude modulation with higher frequency. In contrast to first-order modulation, which appears as a physical component in the stimulus spectrum after half-wave rectification, second-order modulation is not necessarily demodulated by the auditory periphery. For binaural processing of second-order amplitude modulated stimuli it is unknown whether interaural time differences (ITDs) in the second-order modulation result in a lateralized percept. Thus, second-order modulation can serve as a tool to investigate whether demodulation of interaurally delayed components is a prerequisite for lateralization. In most of the psychoacoustic experiments presented here, a 25 Hz sinusoidally amplitude-modulated (SAM) 160 Hz tone was either transposed to 4 kHz by half-wave rectifying this SAM waveform before multiplication with a 4 kHz tone (TSAM), or by adding an offset before multiplication (SAMAM). The experiments revealed an inability to lateralize the SAMAM based on ITDs in the 25 Hz component, whereas subjects could lateralize the TSAM. Given that only the TSAM results in a demodulated 25 Hz component after peripheral auditory processing, this result supports the hypothesis that demodulation is a prerequisite for lateralization, which has consequences for temporal modulation processing in models of binaural interaction.
二阶调幅是一阶调幅调制深度随较高频率的相对缓慢变化。与半波整流后出现在刺激频谱中的一阶调制的物理分量不同，二阶调制不一定需要听觉外围进行解调。对于双耳处理二阶调幅刺激，二阶调制中的耳间时间差（ITD）是否会导致偏向感知尚不清楚。因此，二阶调制可用作工具来研究是否需要对耳间延迟分量进行解调，以便进行侧向化。在本文提出的大多数心理声学实验中，25 Hz 正弦调幅（SAM）160 Hz 音要么通过对半波整流后的 SAM 波形与 4 kHz 音相乘（TSAM）来转换为 4 kHz，要么通过在相乘前添加偏移（SAMAM）来转换。实验表明，基于 25 Hz 分量中的 ITD，无法对 SAMAM 进行侧向化，而受试者可以对 TSAM 进行侧向化。由于只有 TSAM 在经过外围听觉处理后会产生解调的 25 Hz 分量，因此这一结果支持了这样一种假说，即解调是侧向化的前提条件，这对双耳相互作用模型中的时间调制处理具有重要意义。
