均勻平面的視覺消失與知覺填補

Fading, Filling-in, and the Perception of Uniform Surfaces

當視網膜影像固定不動時，因為局部區域適應導致個體知覺快速消失造成視覺消失和知覺填補現象（Gerrits et al., 1984; Troxler, 1804）。此觀察顯示：如果沒有非自主的眼球運動（漂移、眼跳）中，我們是功能性的眼盲。過去20年來，有激增的實驗探討什麼情況會發生視覺消失與知覺填補。隨著長時間注視在凝視點，不管是靜態、移動或閃爍的目標，均會融入背景而看不見（Spillmann et al., 1984）。此類背景未必是均勻而穩定的，具有質地或動態雜訊的背景更是容易產生此類知覺感。有兩個假說可用於說明這兩類現象：（1）端緣選擇細胞使用形狀與色彩的訊息，進行封閉表面的整體亮度和質地的概括化；（2）藉由橫向計算的方式，從邊界主動擴散相關的視覺訊息。目前兩者皆有證據支持此機制可能存在於大腦皮質的V1到V3的區域。視覺消失與知覺填補具有兩種分明的運作階段：邊界的緩慢消除，及周圍背景的快速填入。目前研究爭論聚焦於比較人工視盲區域（變化背景的亮度、色彩和質地）和真實視盲區域（盲點、視網膜病變）的填補。知覺填補只需極少的周圍訊息。例如，在生理盲點周圍呈現一圈極細的紅色環狀區域，仍可引發盲點區域均勻且完整的填補。極細的雙色輪廓亦可誘發跨越大區域的水彩擴散錯覺。這些觀察顯示：具有長距、橫向交互作用的大腦皮質機制可能負責均勻區域的亮度與色彩知覺的運作。

With a stabilized retinal image the percept rapidly disappears from view due to local adaptation, resulting in fading and filling-in (Gerrits, Stassen, & van Erning, 1984; Troxler, 1804). This observation demonstrates that in the absence of involuntary eye movements (drifts, saccades), we are functionally blind. The last twenty years have seen a surge of experiments designed to specify the conditions under which fading and filling-in occur. We know that with prolonged fixation targets assimilate into the background and become invisible, whether static, moving, or flickering (Spillmann, Neumeyer, & Hunzelmann, 1984). Such backgrounds need not be uniform and steady; a textured background or dynamic visual noise are as effective and can be even more so. Two hypotheses may account for fading and filling-in: (i) Generalization of brightness or texture across the enclosed surface region by edge-selective cells using form and color information; and (ii) active spreading of information from the edge by way of lateral propagation. There is evidence for both in cortical areas V1-V3. Two stages for fading and fillingin are distinguished: slow deterioration of the border and fast invasion of the enclosed surface from the surround. Current debate focuses on a comparison between filling-in of artificial scotomata (patches differing from the surround in brightness, color or texture) and real scotomata (blind spot, retinal lesions). We have found that filling-in requires little surround information. For example, a thin red ring hugging the boundary of the physiological blind spot will uniformly and completely fill-in the enclosed blind spot area. Similarly, a thin chromatic double contour will induce watercolor spreading over a wide area. These observations suggest cortical mechanisms involving long-range horizontal interactions to account for brightness and color perception on uniform areas.