Hering 錯視發生階段之探討

Abstract

辨識物體的形狀及物體運動，都要仰賴一個前提要件：亦即該物體的各部分的座標位置必須是已知的，因此物體形狀的改變（形變）與運動訊息都牽涉到改變物體位置登錄碼的動作，然而有些圖形或運動線索卻可在物體之物理形狀與位置維持固定的情況下，誘發視覺空間的扭曲，造成我們的錯覺。這種空間扭曲究竟是在視覺系統登錄位置訊息的時候即已發生，還是在處理形狀問題的階段才發生，便是本論文的探討重點。本研究藉由一個有誘發框架所產生錯視（illusion）圖形（在此選擇Hering 錯視），將它與物理上完全是直線的圖形，以能夠產生運動的時間差交替產生出運動，探討運動系統所接收到的圖形訊息是否受到誘發框架的影響而變形。由於物體位置訊息的抽取在視覺消息處理的流程上居於相當上游的階段，而形狀訊息與運動訊息的分析則發生於較為下游的部位。若錯視是因為圖形位置訊息的扭曲所造成的，則運動系統理應接收到受誘發框架影響而變形的訊息；反之，若錯視的成因不是位置訊息的扭曲，而是更高層次的形狀分析失誤的話，則運動系統應不會受誘發框架的影響，亦即不會有錯視現象的發生。藉由此推理與實驗步驟可幫助我們瞭解錯視的本質，及其發生的生理階段。我們的實驗結果支持以下結論: 1.我們對於形變運動的偵測敏感度是大於靜止的形變偵測。2. Hering 錯視的作用並非發生於運動系統計算運動訊息之前，亦即不可能發生於V1的階段。

We aimed to investigate the anatomical/functional level of shape distortion induced by optical illusions in the current study. Specifically, we tried to determine whether the illusion exerts its effect at the level of position encoding or at a later stage where the more abstract and global form information is derived. The extraction of both form and motion involves the computation of position information. If the optical illusion exerts its effect at the level of V1 where the most accurate position is available, the induced shape change should affect both form and motion perception. If, on the other hand, the shape distortion occurs at a later stage along the what pathway, the motion system could be immune to optical illusions. We used Hering illusion to create perceptually bent lines, and tested if these lines could drive the motion system to produce transformational apparent motion. The results showed that the motion system is blind to the illusion, indicating that the optical illusion does not take its effect at any stage common to form and motion systems.