BRANE Lab, School of Audiology and Speech Sciences, University of British Columbia Vancouver, BC, Canada.
Front Hum Neurosci. 2013 May 21;7:199. doi: 10.3389/fnhum.2013.00199. eCollection 2013.
In adult readers, letters, and words are rapidly identified within visual networks to allow for efficient reading abilities. Neuroimaging studies of orthography have mostly used words and letter strings that recruit many hierarchical levels in reading. Understanding how single letters are processed could provide further insight into orthographic processing. The present study investigated orthographic processing using single letters and pseudoletters when adults were encouraged to pay attention to or away from orthographic features. We measured evoked potentials (EPs) to single letters and pseudoletters from adults while they performed an orthographic-discrimination task (letters vs. pseudoletters), a color-discrimination task (red vs. blue), and a target-detection task (respond to #1 and #2). Larger and later peaking N1 responses (170 ms) and larger P2 responses (250 ms) occurred to pseudoletters as compared to letters. This reflected greater visual processing for pseudoletters. Dipole analyses localized this effect to bilateral fusiform and inferior temporal cortices. Moreover, this letter-pseudoletter difference was not modulated by task and thus indicates that directing attention to or away from orthographic features did not affect early visual processing of single letters or pseudoletters within extrastriate regions. Paying attention to orthography or color as compared to disregarding the stimuli (target-detection task) elicited selection negativities at about 175 ms, which were followed by a classical N2-P3 complex. This indicated that the tasks sufficiently drew participant's attention to and away from the stimuli. Together these findings revealed that visual processing of single letters and pseudoletters, in adults, appeared to be sensory-contingent and independent of paying attention to stimulus features (e.g., orthography or color).
在成年读者中，字母和单词会在视觉网络中迅速被识别，从而实现高效的阅读能力。对正字法的神经影像学研究大多使用单词和字母串，这些单词和字母串在阅读中涉及到许多层次。了解单个字母是如何被处理的，可以进一步深入了解正字法的处理过程。本研究使用单个字母和伪字母来研究正字法处理过程，同时鼓励成年人注意或不注意正字法特征。我们在成年人执行正字法辨别任务（字母与伪字母）、颜色辨别任务（红色与蓝色）和目标检测任务（响应#1 和#2）时，测量了单个字母和伪字母的诱发电位（EP）。与字母相比，伪字母产生的 N1 响应（约 170ms）和 P2 响应（约 250ms）更大且峰值更晚，这反映了伪字母的视觉处理更为复杂。偶极子分析将这种效应定位于双侧梭状回和下颞叶。此外，这种字母-伪字母差异不受任务调节，因此表明，将注意力集中或不集中在正字法特征上，并不影响外侧纹状区单个字母或伪字母的早期视觉处理。与忽略刺激（目标检测任务）相比，关注正字法或颜色会在大约 175ms 时引发选择负波，随后是经典的 N2-P3 复合波。这表明任务足以吸引参与者的注意力并使其远离刺激。这些发现表明，在成年人中，单个字母和伪字母的视觉处理似乎是感官相关的，并且不依赖于注意刺激特征（例如正字法或颜色）。
