Department of Psychology, University of Nevada Reno, NV, USA.
Front Psychol. 2013 Feb 12;4:18. doi: 10.3389/fpsyg.2013.00018. eCollection 2013.
The stimulus requirements for perceiving a face are not well defined but are presumably simple, for vivid faces can often by seen in random or natural images such as cloud or rock formations. To characterize these requirements, we measured where observers reported the impression of faces in images defined by symmetric 1/f noise. This allowed us to examine the prominence and properties of different features and their necessary configurations. In these stimuli many faces can be perceived along the vertical midline, and appear stacked at multiple scales, reminiscent of "totem poles." In addition to symmetry, the faces in noise are invariably upright and thus reveal the inversion effects that are thought to be a defining property of configural face processing. To a large extent, seeing a face required seeing eyes, and these were largely restricted to dark regions in the images. Other features were more subordinate and showed relatively little bias in polarity. Moreover, the prominence of eyes depended primarily on their luminance contrast and showed little influence of chromatic contrast. Notably, most faces were rated as clearly defined with highly distinctive attributes, suggesting that once an image area is coded as a face it is perceptually completed consistent with this interpretation. This suggests that the requisite trigger features are sufficient to holistically "capture" the surrounding noise structure to form the facial representation. Yet despite these well articulated percepts, we show in further experiments that while a pair of dark spots added to noise images appears face-like, these impressions fail to elicit other signatures of face processing, and in particular, fail to elicit an N170 or fixation patterns typical for images of actual faces. These results suggest that very simple stimulus configurations are sufficient to invoke many aspects of holistic and configural face perception while nevertheless failing to fully engage the neural machinery of face coding, implying that that different signatures of face processing may have different stimulus requirements.
感知面部所需的刺激条件尚未明确界定，但推测其条件较为简单，因为生动的面部特征通常可以在随机或自然的图像中被识别，例如云或岩石的形状。为了描述这些条件，我们测量了观察者在由对称 1/f 噪声定义的图像中报告面部印象的位置。这使我们能够检查不同特征的突出性和特性及其必要的配置。在这些刺激中，许多面部特征可以沿着垂直中线被感知，并以多个尺度堆叠，类似于“图腾柱”。除了对称性之外，噪声中的面部特征总是垂直的，因此揭示了被认为是配置面部处理定义属性的反转效应。在很大程度上，看到一个面部特征需要看到眼睛，而这些眼睛主要局限于图像中的暗区。其他特征则较为次要，极性偏差相对较小。此外，眼睛的突出程度主要取决于其亮度对比，而对色度对比的影响较小。值得注意的是，大多数面部特征被评为具有高度独特属性的清晰定义，这表明一旦图像区域被编码为面部，它就会在感知上被完整地完成，与这种解释一致。这表明必要的触发特征足以整体“捕捉”周围的噪声结构，从而形成面部表示。然而，尽管有这些清晰的感知，我们在进一步的实验中表明，虽然在噪声图像中添加一对暗点会使其呈现出面部特征，但这些印象无法引发其他面部处理的特征，特别是无法引发 N170 或与实际面部图像典型的注视模式。这些结果表明，非常简单的刺激配置足以引发整体和配置面部感知的许多方面，而仍然无法完全激活面部编码的神经机制，这意味着不同的面部处理特征可能具有不同的刺激条件。
