邊框在視覺後像色彩上的效果

Abstract

視覺系統暴露在特定顏色的適應刺激（adaptor）下產生適應（adaptation）後，若於測試階段（test phase）放置與適應刺激邊緣相符的邊框（contour），與沒有邊框時相比，負後像（negative afterimage）的對比度會增加；而若將此邊框與適應刺激呈現於不同眼睛的相同位置（dichoptic presenting），會使觀察者在測試階段看到與適應刺激顏色相同的正後像（positive afterimage）。以上述視覺現象為基礎，本研究首先以目標偵測閾限對遮蔽刺激對比函數（target threshold versus pedestal contrast function），觀察不同實驗操弄下目標偵測閾限的上升（對目標機制的抑制）或下降（興奮），來探討適應與邊框對視覺色彩偵測機制的影響。結果顯示適應在低遮蔽刺激對比時有顯著的抑制作用，而此種抑制效果會隨著遮蔽刺激對比增加逐漸減弱。同眼邊框在低遮蔽刺激對比時有興奮效果，在高遮蔽刺激對比時則有抑制效果；另一方面，異眼邊框則只在低遮蔽刺激對比時有顯著的抑制效果。最後，若在適應後加入這兩種邊框，仍可觀察到邊框的效果造成的資料趨勢。根據上述結果，我們以過去在圖形偵測研究中，能解釋類似函數形狀變異的除法抑制（divisive inhibition）及側邊敏感度調節（lateral sensitivity modulation）模型進行擬合，適配度較高的結果顯示受邊框造成的側邊互動（lateral interaction）所影響的模型參數與過去研究並不一致，除了暗示色彩與圖形偵測機制的相異之外，也為色彩訊號的雙眼整合（binocular summation）機制提供了初步的線索。

After adapting to a specific color, a contour that fits the edge of the adaptor in the test phase can enhance the contrast of the negative afterimage. Moreover, if the contour is presented dichoptically with the adaptor, the observer will see a positive afterimage. In the current study, we conducted an experiment to measure the target threshold versus pedestal contrast function (TvC function) under different adaptor and contour presenting conditions. The results indicated that adaptation had a significant inhibition effect at low pedestal contrast, which weakened as the pedestal contrast increased. Additionally, the same-eye contour had an excitation effect at low pedestal contrast and an inhibition effect at high pedestal contrast, whereas the cross-eye contour had a significant inhibition effect only at low pedestal contrast. Furthermore, the effect of the contour was weakened with adaptation, but the trend still remained. These data were fitted with divisive inhibition and lateral sensitivity modulation models that explain similar variations observed in past research on pattern detection. The model fitting results showed that the parameters required to explain the effect of contour were inconsistent with pattern detection. The results reveal the difference between the two detection mechanisms and offer evidence regarding the binocular summation of color signals.