Yet another optical illusion

剛發現了一個尚未看過的錯覺影像（optical illusion）。下圖裡的圖樣在適當的距離下看起來似乎會抖動。這類的錯覺我還不知道怎麼歸類。請知道的人不吝指教。

I just produced an image that seems to trigger quivering optical illusion at a proper viewing distance.  I do not recall having seen such sort of quivering effect before. Any explanation will be highly appreciated. The image has been generated via frequency domain quadrature filtering(middle) on an image(bottom) from [1].

rev_107_4_677_fig3a-s-A15-Q0.3-w0.9-N6-F0.8-pz0-w6.png

下圖為產生上圖 quadrature filtering 的 transfer function。每一個 frequency domain 的 Gabor function 的 aspect ratio 為 0.3。最高的 center frequency 為 0.9 Nyquist，較低的 center frequencies 分別為 0.72、0.576、 0.46、0.37、0.3 Nyquist。Radial bandwidth 為 1 octave，orientation bandwidth 為 15 degrees。

下圖為取自 [1] 的原始影像： http://psycnet.apa.org/journals/rev/107/4/images/rev_107_4_677_fig3a.gif

[1] Wilson S. Geisler and Boaz J. Super,
     Perceptual organization of two-dimensional patterns,
     Psychological Review, Vol 107(4), Oct 2000, 677-708.
     http://psycnet.apa.org/index.cfm?fa=buy.optionToBuy&id=2000-02818-002