Adults struggle to learn non-native speech contrasts even after years of exposure. While laboratory-based training approaches yield learning, the optimal training conditions for maximizing speech learning in adulthood are currently unknown. Vagus nerve stimulation has been shown to prime adult sensory-perceptual systems towards plasticity in animal models. Precise temporal pairing with auditory stimuli can enhance auditory cortical representations with a high degree of specificity. Here, we examined whether sub-perceptual threshold transcutaneous vagus nerve stimulation (tVNS), paired with non-native speech sounds, enhances speech category learning in adults. Twenty-four native English-speakers were trained to identify non-native Mandarin tone categories. Across two groups, tVNS was paired with the tone categories that were easier- or harder-to-learn. A control group received no stimulation but followed an identical thresholding procedure as the intervention groups. We found that tVNS robustly enhanced speech category learning and retention of correct stimulus-response associations, but only when stimulation was paired with the easier-to-learn categories. This effect emerged rapidly, generalized to new exemplars, and was qualitatively different from the normal individual variability observed in hundreds of learners who have performed in the same task without stimulation. Electroencephalography recorded before and after training indicated no evidence of tVNS-induced changes in the sensory representation of auditory stimuli. These results suggest that paired-tVNS induces a temporally precise neuromodulatory signal that selectively enhances the perception and memory consolidation of perceptually salient categories.

即使经过多年的接触，成年人仍难以学习非母语的语音对比。尽管基于实验室的培训方法可以产生学习效果，但目前尚不清楚用于最大化成年语音学习的最佳培训条件。在动物模型中，迷走神经刺激已被证明可以使成年感官知觉系统趋于可塑性。精确的时间配对与听觉刺激可以高度特异性地增强听觉皮层表现。在这里，我们研究了知觉阈以下经皮迷走神经刺激（tVNS），与非母语语音配对，是否能增强成人的语音类别学习。培训了24位讲英语的母语人士，以识别非母语普通话类别。在两组之间 tVNS与更容易或更难学习的音调类别配对。对照组未接受刺激，但遵循与干预组相同的阈值程序。我们发现tVNS可以强有力地增强语音类别的学习并保持正确的刺激-反应联想，但前提是刺激与易于学习的类别配对使用。这种影响迅速出现，并推广到新的范例中，并且在质量上与数百名在没有刺激的情况下完成相同任务的学习者中观察到的正常个体变异性不同。训练前后记录的脑电图表明，没有证据表明tVNS引起听觉刺激的感觉代表变化。