走走停停錯覺：注意力與運動訊息對運動知覺之影響

Abstract

Anstis （2001） 發現在「腳步錯覺」（footsteps illusion）中，移動中物體的對比（contrast）會影響對物體的速度知覺。物體的移動在對比低的情況下速度會減慢，並且在完全沒有任何對比差異時完全停下來。過去以對比和運動偵測相關的低階機轉解釋錯覺的產生，並且將完全停下來的原因訴諸低對比下運動訊號的缺乏。然而另一個相似的「走走停停」錯覺—扇子錯覺（fan illusion）卻受注意力操弄的影響（Yeh、Chiu 和Hsiao，2007）。我們透過實驗一與二連結兩種錯覺，發現不論是否有運動訊息，扇子與腳步錯覺都受對比的影響，不過受影響的方式卻與過去的解釋（Howe et al.，2006）不符。由於物體遮蔽時的追蹤需要注意力資源（attentive tracking），實驗三證實注意力為基的視覺追蹤確實影響「走走停停」的錯覺現象。因此，我們透過本研究連結兩項解釋上完全不同的錯覺現象，提出兩者背後具有共同的運作機轉，並認為對物體的運動知覺是由運動訊號與物體追蹤機轉決定，前者受物體對比影響，而後者仰賴注意力維持。

In the footsteps illusion (Anstis, 2001), motion speeds up at high contrasts and slows down at low contrasts, coming to a complete halt at equiluminance. Such speed change has been attributed to low-level contrast-dependent mechanisms, with motion signals completely absent at equiluminance. However, a seemingly similar illusion that also shows the “stopping” illusion, the fan illusion, has been shown to be affected by attention (Yeh, Chiu, & Hsiao, 2007). To link the footsteps illusions with the fan illusion, we demonstrated that in the presence and absence of motion signals, both the footsteps and fan illusions are similarly affected by contrast (Experiment 1and 2), but in ways that are inconsistent with previous explanations (Howe, Thompson, Anstis, Sagreiya, & Livingstone, 2006). In Experiment 3, we further showed that manipulation of attentive tracking influenced illusion strength. We conclude that both contrast-dependent motion perception and attentive tracking determine perceived speed in the two illusions.