Unité Cognition et développement and Laboratoire de Neurophysiologie, Université catholique de Louvain, Belgium.
Brain Res. 2010 Mar 8;1318:96-109. doi: 10.1016/j.brainres.2009.12.070. Epub 2010 Jan 4.
The N170 is an occipito-temporal visual event-related potential that is larger in response to faces than other nonface object categories and has been associated with the early activation of visual face representations in the human brain. It has been recently showed that spatially misaligning the bottom and top halves of a face stimulus-a manipulation used in behavioural studies to disrupt the processing of the whole face configuration (i.e. holistic processing)-increases the latency and the amplitude of the N170, particularly in the right hemisphere. Here we show that these observations cannot be accounted for by a general effect of spatial misalignment of visual patterns. A first experiment showed that the effect of misalignment on the N170 was larger when both top and bottom halves of the stimulus were made of face parts (i.e. a full face) compared to when one of the two halves was made of visual noise. The N170 delay and increase for misaligned faces is similar to the effect of upside-down face inversion, a manipulation thought to disrupt holistic processing. Supporting this view, in a second experiment in which we presented upside-down versions of the stimuli used in the first experiment, we did not observe such a larger effect of misalignment on the N170 for a full face compared to the control conditions. These observations support the view that the early face representation activated in the human brain at the level of the N170, is that of a global upright face pattern. Specifically, when the global configuration of a face is modified by inverting it or spatially misaligning its top and bottom halves, the activation of its representation is delayed in cortical areas coding preferentially for faces. Moreover, when the global face configuration is disrupted, the face stimulus appears to recruit additional neural processes compared to normal face processing, leading to an increase of the N170 amplitude on the scalp.
N170 是一种枕颞部视觉事件相关电位，对人脸的反应比其他非人脸物体类别更大，与人类大脑中视觉面部表征的早期激活有关。最近的研究表明，空间上错开面部刺激的上下半部分（一种用于行为研究的操作，以破坏整个面部配置的处理，即整体处理）会增加 N170 的潜伏期和振幅，特别是在右半球。在这里，我们表明这些观察结果不能用视觉模式的空间错位的一般效应来解释。第一个实验表明，当刺激的上下两半都由面部部分（即完整的脸）组成时，与两个半部分之一由视觉噪声组成相比，错位对 N170 的影响更大。N170 延迟和增加对于错位的面孔与面孔倒置的效果相似，这种操作被认为会破坏整体处理。支持这一观点，在第二个实验中，我们呈现了第一个实验中使用的刺激的倒置版本，我们没有观察到对于完整的面孔，与对照条件相比，N170 对于错位的更大影响。这些观察结果支持这样的观点，即在 N170 水平上激活的人类大脑中的早期面部表征是整体直立的面部模式。具体来说，当面部的整体配置通过倒置或空间上错开其上下半部分而改变时，其表示的激活在编码优先对面部的皮质区域中被延迟。此外，当整体面部配置受到干扰时，与正常的面部处理相比，面部刺激似乎会招募额外的神经过程，导致头皮上 N170 振幅增加。
