Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, PO Box 9101, 6500 HB, Nijmegen, The Netherlands.
Neuropsychologia. 2013 Aug;51(10):1802-13. doi: 10.1016/j.neuropsychologia.2013.06.024. Epub 2013 Jul 4.
Grapheme-color synesthetes perceive color when reading letters or digits. We investigated oscillatory brain signals of synesthetes vs. controls using magnetoencephalography. Brain oscillations specifically in the alpha band (∼10Hz) have two interesting features: alpha has been linked to inhibitory processes and can act as a marker for attention. The possible role of reduced inhibition as an underlying cause of synesthesia, as well as the precise role of attention in synesthesia is widely discussed. To assess alpha power effects due to synesthesia, synesthetes as well as matched controls viewed synesthesia-inducing graphemes, colored control graphemes, and non-colored control graphemes while brain activity was recorded. Subjects had to report a color change at the end of each trial which allowed us to assess the strength of synesthesia in each synesthete. Since color (synesthetic or real) might allocate attention we also included an attentional cue in our paradigm which could direct covert attention. In controls the attentional cue always caused a lateralization of alpha power with a contralateral decrease and ipsilateral alpha increase over occipital sensors. In synesthetes, however, the influence of the cue was overruled by color: independent of the attentional cue, alpha power decreased contralateral to the color (synesthetic or real). This indicates that in synesthetes color guides attention. This was confirmed by reaction time effects due to color, i.e. faster RTs for the color side independent of the cue. Finally, the stronger the observed color dependent alpha lateralization, the stronger was the manifestation of synesthesia as measured by congruency effects of synesthetic colors on RTs. Behavioral and imaging results indicate that color induces a location-specific, automatic shift of attention towards color in synesthetes but not in controls. We hypothesize that this mechanism can facilitate coupling of grapheme and color during the development of synesthesia.
文字-颜色联觉者在阅读字母或数字时会感知到颜色。我们使用脑磁图研究了联觉者和对照组的脑振荡信号。脑振荡，特别是在 alpha 波段（约 10Hz），具有两个有趣的特征：alpha 与抑制过程有关，并且可以作为注意力的标记。作为联觉的潜在原因的抑制减少的可能作用，以及注意力在联觉中的精确作用，被广泛讨论。为了评估由于联觉而产生的 alpha 功率效应，我们让联觉者和匹配的对照组观看了诱发联觉的字母、彩色控制字母和非彩色控制字母，同时记录大脑活动。在每个试验结束时，受试者必须报告颜色变化，这使我们能够评估每个联觉者的联觉强度。由于颜色（联觉或真实）可能会分配注意力，我们在范式中还包括了一个注意力提示，可以引导隐蔽注意力。在对照组中，注意力提示总是导致 alpha 功率的侧化，对侧alpha 功率降低，对侧 alpha 功率增加。然而，在联觉者中，提示的影响被颜色所推翻：无论注意力提示如何，alpha 功率都在颜色（联觉或真实）的对侧下降。这表明在联觉者中，颜色引导注意力。这通过颜色引起的反应时间效应得到了证实，即无论提示如何，颜色侧的反应时间都更快。最后，观察到的依赖颜色的 alpha 侧化越强，作为联觉颜色对 RT 影响的一致性效应来衡量的联觉表现就越强。行为和成像结果表明，颜色在联觉者中引起了位置特异性的、自动的注意力向颜色的转移，而在对照组中则没有。我们假设这种机制可以促进联觉发展过程中文字和颜色的耦合。
