University of California, San Diego, La Jolla, CA 92093, USA.
J Cogn Neurosci. 2011 Jul;23(7):1681-96. doi: 10.1162/jocn.2010.21486. Epub 2010 Mar 29.
Grapheme-color synesthesia is a heritable trait where graphemes ("2") elicit the concurrent perception of specific colors (red). Researchers have questioned whether synesthetic experiences are meaningful or simply arbitrary associations and whether these associations are perceptual or conceptual. To address these fundamental questions, ERPs were recorded as 12 synesthetes read statements such as "The Coca-Cola logo is white and 2," in which the final grapheme induced a color that was either contextually congruous (red) or incongruous ("...white and 7," for a synesthetes who experienced 7 as green). Grapheme congruity was found to modulate the amplitude of the N1, P2, N300, and N400 components in synesthetes, suggesting that synesthesia impacts perceptual as well as conceptual aspects of processing. To evaluate whether observed ERP effects required the experience of colored graphemes versus knowledge of grapheme-color pairings, we ran three separate groups of controls on a similar task. Controls trained to a synesthete's associations elicited N400 modulation, indicating that knowledge of grapheme-color mappings was sufficient to modulate this component. Controls trained to synesthetic associations and given explicit visualization instructions elicited both N300 and N400 modulations. Lastly, untrained controls who viewed physically colored graphemes ("2" printed in red) elicited N1 and N400 modulations. The N1 grapheme congruity effect began earlier in synesthetes than colored grapheme controls but had similar scalp topography. Data suggest that, in synesthetes, achromatic graphemes engage similar visual processing networks as colored graphemes in nonsynesthetes and are in keeping with models of synesthesia that posit early feed-forward connections between form and color processing areas in extrastriate cortex. The P2 modulation was unique to the synesthetes and may reflect neural activity that underlies the conscious experience of the synesthetic induction.
文字-颜色联觉是一种遗传性特质，其中文字（“2”）会引发对特定颜色（红色）的同时感知。研究人员质疑联觉体验是否有意义，或者只是任意的联想，以及这些联想是感知的还是概念的。为了解决这些基本问题，研究人员记录了 12 位联觉者阅读以下句子时的脑电活动：“可口可乐的标志是白色和 2”，其中最后一个文字会引发一种颜色，这种颜色要么与上下文一致（红色），要么不一致（“...白色和 7”，对于体验 7 为绿色的联觉者来说）。研究发现，文字一致性会调节联觉者的 N1、P2、N300 和 N400 成分的振幅，表明联觉会影响处理的感知和概念方面。为了评估观察到的 ERP 效应是否需要体验彩色文字或了解文字-颜色配对，我们在类似的任务中对三组独立的对照组进行了测试。对照组根据联觉者的联想进行训练，会引起 N400 调制，表明对文字-颜色映射的了解足以调节这个成分。对照组根据联觉联想进行训练，并给予明确的可视化指导，会引起 N300 和 N400 的调制。最后，未受过训练的对照组看到物理上色的文字（“2”印成红色），会引起 N1 和 N400 的调制。N1 文字一致性效应在联觉者中比彩色文字对照组更早开始，但头皮地形图相似。数据表明，在联觉者中，无颜色的文字会与非联觉者中彩色文字一样，激活相似的视觉处理网络，这与联觉的模型一致，即假设在外侧纹状皮层中，形式和颜色处理区域之间存在早期的前馈连接。P2 调制是联觉者所特有的，可能反映了意识诱导联觉体验的神经活动。
