Wilson Hugh R, Loffler Gunter, Wilkinson Frances
Centre for Vision Research, York University, Toronto, Canada.
Vision Res. 2002 Dec;42(27):2909-23. doi: 10.1016/s0042-6989(02)00362-0.
To simplify the study of visual face processing, we introduce a novel class of synthetic face stimuli based upon 37 measurements (head shape, feature locations, etc.) extracted from individual face photographs in both frontal and 20 degrees side views. Synthetic faces are bandpass filtered optimally for face perception and include both line and edge information. Pilot experiments establish that subjects are extremely accurate in matching a synthetic face with the original grayscale photograph, even across views. To determine the perceptual metric of face space, we introduce face cubes in which the geometric differences between any faces in a four-dimensional face subspace can be precisely determined. Experiments on face discrimination using face cubes establish the metric of synthetic face space as locally Euclidean, with discrimination thresholds representing 4-6% total geometric variation (as a percent of mean head radius) between faces. Discrimination thresholds are lowest for face cubes constructed around the average face, thus indicating that the mean face for each gender represents a natural origin for face space. Finally, synthetic faces exhibit a pronounced inversion effect for 20 degrees side views and a characteristic "Thatcher effect" for inverted front views. Synthetic faces and face cubes thus provide a useful new quantitative approach to the study of face perception and face space.
为了简化对面部视觉处理的研究，我们基于从正面和20度侧视图的个人面部照片中提取的37项测量数据（头部形状、特征位置等），引入了一类新型的合成面部刺激物。合成面部经过优化的带通滤波以用于面部感知，并且包含线条和边缘信息。初步实验表明，即使在不同视图下，受试者在将合成面部与原始灰度照片进行匹配时也极其准确。为了确定面部空间的感知度量，我们引入了面部立方体，其中可以精确确定四维面部子空间中任意两个面部之间的几何差异。使用面部立方体进行的面部辨别实验确定了合成面部空间的度量为局部欧几里得度量，辨别阈值表示面部之间总几何变化的4-6%（作为平均头部半径的百分比）。围绕平均面部构建的面部立方体的辨别阈值最低，这表明每个性别的平均面部代表了面部空间的自然原点。最后，合成面部在20度侧视图中表现出明显的倒置效应，在倒置的前视图中表现出特征性的“撒切尔效应”。因此，合成面部和面部立方体为面部感知和面部空间的研究提供了一种有用的新定量方法。
