Regan D, Regan M P
Department of Ophthalmology, Dalhousie University, Halifax, Nova Scotia, Canada.
Vision Res. 1987;27(12):2181-3. doi: 10.1016/0042-6989(87)90132-5.
Subjects viewed a pattern consisting of two superimposed gratings: a vertical grating that was counterphase-modulated at Fl Hz and a variable-orientation grafting modulated at F2 Hz. A nonlinear orientation-tuned cross-modulation term of frequency (2F1 + 2K2)Hz in the evoked potential was large when the gratings were parallel and had a half-height full bandwidth of about 12 deg. But a strong (2F1 + 2F2) term was also produced by orthogonal gratings. The application of Fourier methods to analyzing human visual processing of patterns modulated in two dimensions assumes that there is no nonlinear interaction between visual responses to orthogonal gratings. The existence of a strong cross-modulation term in the orthogonal-grating response violates this crucial requirement. Our findings could not result from the stimulation of independent, linear, orientation-selective mechanisms.
一个以F1赫兹进行反相调制的垂直光栅和一个以F2赫兹进行调制的可变方向光栅。当光栅平行时，诱发电位中频率为（2F1 + 2K2）赫兹的非线性方向调谐交叉调制项很大，其半高全宽约为12度。但是正交光栅也会产生一个很强的（2F1 + 2F2）项。将傅里叶方法应用于分析人类对二维调制图案的视觉处理时，假设对正交光栅的视觉反应之间不存在非线性相互作用。正交光栅反应中存在很强的交叉调制项违反了这一关键要求。我们的发现不可能是由独立的、线性的、方向选择性机制的刺激导致的。
