Neural activity tracks the envelope of a speech signal at latencies from 50 ms to 300 ms. Modulating this neural tracking through transcranial alternating current stimulation influences speech comprehension. Two important variables that can affect this modulation are the latency and the phase of the stimulation with respect to the sound. While previous studies have found an influence of both variables on speech comprehension, the interaction between both has not yet been measured. We presented 17 subjects with speech in noise coupled with simultaneous transcranial alternating current stimulation. The currents were based on the envelope of the target speech but shifted by different phases, as well as by two temporal delays of 100 ms and 250 ms. We also employed various control stimulations, and assessed the signal-to-noise ratio at which the subject understood half of the speech. We found that, at both latencies, speech comprehension is modulated by the phase of the current stimulation. However, the form of the modulation differed between the two latencies. Phase and latency of neurostimulation have accordingly distinct influences on speech comprehension. The different effects at the latencies of 100 ms and 250 ms hint at distinct neural processes for speech processing.

中文翻译：

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通过经相移语音包络的经颅电流刺激对语音中的语音理解进行调制。

神经活动以50 ms至300 ms的延迟跟踪语音信号的包络。通过经颅交流电刺激调节这种神经跟踪会影响语音理解。可以影响这种调制的两个重要变量是潜伏期和相对于声音的刺激相位。尽管先前的研究已经发现这两个变量都对语音理解产生影响，但尚未测量这两个变量之间的相互作用。我们提出了17名受试者的语音噪声与同时经颅交流电刺激相结合。电流基于目标语音的包络，但相移不同，以及两个100 ms和250 ms的时间延迟。我们还采用了各种控制刺激 并评估了受试者理解一半语音的信噪比。我们发现，在两种等待时间下，语音理解均受当前刺激的相位调制。但是，两个延迟之间的调制形式有所不同。因此，神经刺激的阶段和潜伏期对语音理解有明显的影响。延迟为100 ms和250 ms的不同效果暗示了语音处理的不同神经过程。