Carey Daniel, Miquel Marc E, Evans Bronwen G, Adank Patti, McGettigan Carolyn
Department of Psychology, Royal Holloway, University of London, London TW20 0EX, UK.
Combined Universities Brain Imaging Centre, Royal Holloway, University of London, London TW20 0EX, UK.
Cereb Cortex. 2017 May 1;27(5):3064-3079. doi: 10.1093/cercor/bhx056.
Imitating speech necessitates the transformation from sensory targets to vocal tract motor output, yet little is known about the representational basis of this process in the human brain. Here, we address this question by using real-time MR imaging (rtMRI) of the vocal tract and functional MRI (fMRI) of the brain in a speech imitation paradigm. Participants trained on imitating a native vowel and a similar nonnative vowel that required lip rounding. Later, participants imitated these vowels and an untrained vowel pair during separate fMRI and rtMRI runs. Univariate fMRI analyses revealed that regions including left inferior frontal gyrus were more active during sensorimotor transformation (ST) and production of nonnative vowels, compared with native vowels; further, ST for nonnative vowels activated somatomotor cortex bilaterally, compared with ST of native vowels. Using test representational similarity analysis (RSA) models constructed from participants' vocal tract images and from stimulus formant distances, we found that RSA searchlight analyses of fMRI data showed either type of model could be represented in somatomotor, temporal, cerebellar, and hippocampal neural activation patterns during ST. We thus provide the first evidence of widespread and robust cortical and subcortical neural representation of vocal tract and/or formant parameters, during prearticulatory ST.
模仿语音需要从感觉目标转换为声道运动输出，但对于人类大脑中这一过程的表征基础却知之甚少。在此，我们通过在语音模仿范式中使用声道实时磁共振成像（rtMRI）和大脑功能磁共振成像（fMRI）来解决这个问题。参与者接受训练以模仿一个母语元音和一个需要圆唇的类似非母语元音。之后，参与者在单独的fMRI和rtMRI扫描过程中模仿这些元音以及一对未训练过的元音。单变量fMRI分析显示，与母语元音相比，包括左额下回在内的区域在感觉运动转换（ST）和非母语元音发音过程中更为活跃；此外，与母语元音的ST相比，非母语元音的ST双侧激活了躯体运动皮层。使用根据参与者的声道图像和刺激共振峰距离构建的测试表征相似性分析（RSA）模型，我们发现对fMRI数据进行的RSA探照灯分析表明，在ST过程中，两种类型的模型都可以在躯体运动、颞叶、小脑和海马神经激活模式中得到体现。因此，我们首次提供了证据，表明在发音前的ST过程中，声道和/或共振峰参数在广泛且稳定的皮层和皮层下神经表征中存在。
