Harris Joseph A, Wu Chien-Te, Woldorff Marty G
Center for Cognitive Neuroscience, Duke University, Durham, NC, USA.
J Vis. 2011 Jun 7;11(7):10.1167/11.7.3 3. doi: 10.1167/11.7.3.
It is generally agreed that considerable amounts of low-level sensory processing of visual stimuli can occur without conscious awareness. On the other hand, the degree of higher level visual processing that occurs in the absence of awareness is as yet unclear. Here, event-related potential (ERP) measures of brain activity were recorded during a sandwich-masking paradigm, a commonly used approach for attenuating conscious awareness of visual stimulus content. In particular, the present study used a combination of ERP activation contrasts to track both early sensory-processing ERP components and face-specific N170 ERP activations, in trials with versus without awareness. The electrophysiological measures revealed that the sandwich masking abolished the early face-specific N170 neural response (peaking at ~170 ms post-stimulus), an effect that paralleled the abolition of awareness of face versus non-face image content. Furthermore, however, the masking appeared to render a strong attenuation of earlier feedforward visual sensory-processing signals. This early attenuation presumably resulted in insufficient information being fed into the higher level visual system pathways specific to object category processing, thus leading to unawareness of the visual object content. These results support a coupling of visual awareness and neural indices of face processing, while also demonstrating an early low-level mechanism of interference in sandwich masking.
人们普遍认为，视觉刺激的大量低水平感觉处理可以在没有意识觉知的情况下发生。另一方面，在无意识状态下发生的高级视觉处理程度尚不清楚。在这里，在三明治掩蔽范式中记录了与事件相关的脑电活动（ERP）测量值，这是一种常用的减弱对视觉刺激内容的意识觉知的方法。具体而言，本研究在有意识和无意识的试验中，使用ERP激活对比的组合来追踪早期感觉处理ERP成分和面部特异性N170 ERP激活。电生理测量结果显示，三明治掩蔽消除了早期面部特异性N170神经反应（在刺激后约170毫秒达到峰值），这一效应与对面部与非面部图像内容的意识觉知消除相平行。然而，此外，掩蔽似乎使早期的前馈视觉感觉处理信号大幅衰减。这种早期衰减可能导致输入到特定于物体类别处理的高级视觉系统通路的信息不足，从而导致对视觉物体内容的无意识。这些结果支持了视觉觉知与面部处理神经指标的耦合，同时也证明了三明治掩蔽中干扰的早期低水平机制。
