York Neuroimaging Centre, University of York, York, United Kingdom.
PLoS One. 2012;7(4):e34668. doi: 10.1371/journal.pone.0034668. Epub 2012 Apr 3.
In this study we investigate whether stimulus variability affects the auditory steady-state response (ASSR). We present cosinusoidal AM pulses as stimuli where we are able to manipulate waveform shape independently of the fixed repetition rate of 4 Hz. We either present sounds in which the waveform shape, the pulse-width, is fixed throughout the presentation or where it varies pseudo-randomly. Importantly, the average spectra of all the fixed-width AM stimuli are equal to the spectra of the mixed-width AM. Our null hypothesis is that the average ASSR to the fixed-width AM will not be significantly different from the ASSR to the mixed-width AM. In a region of interest beamformer analysis of MEG data, we compare the 4 Hz component of the ASSR to the mixed-width AM with the 4 Hz component of the ASSR to the pooled fixed-width AM. We find that at the group level, there is a significantly greater response to the variable mixed-width AM at the medial boundary of the Middle and Superior Temporal Gyri. Hence, we find that adding variability into AM stimuli increases the amplitude of the ASSR. This observation is important, as it provides evidence that analysis of the modulation waveform shape is an integral part of AM processing. Therefore, standard steady-state studies in audition, using sinusoidal AM, may not be sensitive to a key feature of acoustic processing.
在这项研究中，我们调查了刺激变异性是否会影响听觉稳态反应（ASSR）。我们提出了余弦调幅（AM）脉冲作为刺激，我们能够独立于 4 Hz 的固定重复率来操纵波形形状。我们要么呈现整个呈现过程中波形形状（脉冲宽度）固定的声音，要么呈现波形形状随机变化的声音。重要的是，所有固定宽度 AM 刺激的平均频谱都等于混合宽度 AM 的频谱。我们的零假设是，固定宽度 AM 的平均 ASSR 不会与混合宽度 AM 的 ASSR 有显著差异。在感兴趣区域的脑磁图（MEG）数据的波束形成分析中，我们将混合宽度 AM 的 ASSR 的 4 Hz 分量与混合宽度 AM 的 ASSR 的 4 Hz 分量与汇总的固定宽度 AM 的 ASSR 的 4 Hz 分量进行比较。我们发现，在群体水平上，在中颞回和上颞回的内侧边界处，混合宽度 AM 的可变刺激会引起明显更大的反应。因此，我们发现向 AM 刺激中添加变异性会增加 ASSR 的幅度。这一观察结果很重要，因为它提供了证据表明，对调制波形形状的分析是 AM 处理的一个组成部分。因此，使用正弦 AM 的听觉标准稳态研究可能对声音处理的一个关键特征不敏感。
