Sierra-Vázquez Vicente, Serrano-Pedraza Ignacio
Departamento de Psicología Básica I, Facultad de Psicología, Universidad Complutense de Madrid, Campus de Somosaguas, 28223 Madrid, Spain.
J Opt Soc Am A Opt Image Sci Vis. 2010 Apr 1;27(4):781-96. doi: 10.1364/JOSAA.27.000781.
The existence of a special second-order mechanism in the human visual system, able to demodulate the envelope of visual stimuli, suggests that spatial information contained in the image envelope may be perceptually relevant. The Riesz transform, a natural isotropic extension of the Hilbert transform to multidimensional signals, was used here to demodulate band-pass filtered images of well-known visual illusions of length, size, direction, and shape. We show that the local amplitude of the monogenic signal or envelope of each illusion image conveys second-order information related to image holistic spatial structure, whereas the local phase component conveys information about the spatial features. Further low-pass filtering of the illusion image envelopes creates physical distortions that correspond to the subjective distortions perceived in the illusory images. Therefore the envelope seems to be the image component that physically carries the spatial information about these illusions. This result contradicts the popular belief that the relevant spatial information to perceive geometrical-optical illusions is conveyed only by the lower spatial frequencies present in their Fourier spectrum.
人类视觉系统中存在一种特殊的二阶机制，能够解调视觉刺激的包络，这表明图像包络中包含的空间信息可能在感知上具有相关性。里兹变换是希尔伯特变换到多维信号的自然各向同性扩展，在此用于解调长度、大小、方向和形状等著名视觉错觉的带通滤波图像。我们表明，每个错觉图像的单演信号的局部幅度或包络传达了与图像整体空间结构相关的二阶信息，而局部相位分量传达了有关空间特征的信息。对错觉图像包络的进一步低通滤波会产生与错觉图像中感知到的主观失真相对应的物理失真。因此，包络似乎是物理上承载这些错觉空间信息的图像成分。这一结果与普遍看法相矛盾，即感知几何光学错觉的相关空间信息仅由其傅里叶频谱中存在的较低空间频率传达。
