Johns Hopkins University, Baltimore, MD.
J Cogn Neurosci. 2023 Oct 1;35(10):1593-1616. doi: 10.1162/jocn_a_02041.
Blind readers use a tactile reading system consisting of raised dot arrays: braille/⠃⠗⠇. How do human brains implement reading by touch? The current study looked for signatures of reading-specific orthographic processes in braille, separate from low-level somatosensory responses and semantic processes. Of specific interest were responses in posterior parietal cortices (PPCs), because of their role in high-level tactile perception. Congenitally blind, proficient braille readers read real words and pseudowords by touch while undergoing fMRI. We leveraged the system of contractions in English braille, where one braille cell can represent multiple English print letters (e.g., "ing" ⠬, "one" ⠐⠕), making it possible to separate physical and orthographic word length. All words in the study consisted of four braille cells, but their corresponding Roman letter spellings varied from four to seven letters (e.g., "con-c-er-t" ⠒⠉⠻⠞. contracted: four cells; uncontracted: seven letters). We found that the bilateral supramarginal gyrus in the PPC increased its activity as the uncontracted word length increased. By contrast, in the hand region of primary somatosensory cortex (S1), activity increased as a function of a low-level somatosensory feature: dot-number per word. The PPC also showed greater response to pseudowords than real words and distinguished between real and pseudowords in multivariate-pattern analysis. Parieto-occipital, early visual and ventral occipito-temporal, as well as prefrontal cortices also showed sensitivity to the real-versus-pseudoword distinction. We conclude that PPC is involved in orthographic processing for braille, that is, braille character and word recognition, possibly because of braille's tactile modality.
盲文/⠃⠗⠇。人类大脑如何通过触摸实现阅读？本研究旨在寻找盲文阅读中特定于阅读的正字法过程的特征，这些特征与低水平的体感反应和语义过程分开。特别感兴趣的是顶后皮质（PPC）的反应，因为它们在高级触觉感知中起作用。先天性失明、熟练的盲文读者在进行 fMRI 时通过触摸阅读真实单词和伪单词。我们利用英语盲文的收缩系统，其中一个盲文单元可以表示多个英语印刷字母（例如，“ing” ⠬，“one” ⠐⠕），从而可以将物理和正字法长度分开。研究中的所有单词都由四个盲文单元组成，但它们对应的罗马字母拼写从四个到七个字母不等（例如，“con-c-er-t” ⠒⠉⠻⠞. 收缩：四个单元；未收缩：七个字母）。我们发现，PPC 的双侧缘上回随着未收缩单词长度的增加而增加其活动。相比之下，在初级体感皮层（S1）的手部区域，活动随着低水平体感特征（每个单词的点数）而增加。PPC 对伪单词的反应也大于真实单词，并在多元模式分析中区分真实单词和伪单词。顶枕叶、早期视觉和腹侧枕颞叶以及前额叶皮层也表现出对真实与伪单词区分的敏感性。我们得出结论，PPC 参与盲文的正字法处理，即盲文字符和单词识别，这可能是因为盲文的触觉方式。
