知覺群聚中的多重色彩機制

Abstract

本研究探討知覺群聚（perceptual grouping）中色彩視覺機制（color vision mechanisms）的調頻（tuning）與反應（response）特性。實驗材料由數組隨機分布於影像中的「三點」（tripole）組成，定錨點（anchor dot）決定每組三點的隨機位置，另外兩個周邊點（context dots）的位置取決於其與定錨點位置間的幾何關係。若將定錨點與其中一個周邊點組合在一起，觀察者可能看到順時針或逆時針螺旋形狀的整體圖形。定錨點的色度（chromaticity）均勻分布在色彩空間中的等亮度平面（equiluminant plane）上，其中一個周邊點的色度和定錨點色度相同，另一個周邊點色度相對於定錨點色度變化。兩個周邊點的色彩對比（color contrast）落於一至四倍該色度之偵測閾值（detection threshold）範圍間。受試者回答看到的實驗刺激為順時針或逆時針螺旋圖形。結果顯示，將定錨點與其一周邊點組合在一起的機率隨著該周邊點的色彩對比上升而上升，但隨著另一周邊點的色彩對比上升而下降，暗示兩種組合方式互相競爭觀察者的圖形覺知（percept）。無論定錨點色度，將定錨點與周邊點組合的機率隨著兩點間的色度差異增加而下降。包含四組色彩機制的除法抑制模型（divisive inhibition model）可解釋上述觀察現象，其中兩組色彩機制的調頻函數（tuning functions）與過去文獻中的紅綠（L-M）及藍黃（S-[L-M]）機制相似，另外兩組則偏好其他中間顏色。此研究指出知覺群聚中涉及紅綠與藍黃以外的色彩機制。

This study investigated the tuning and response properties of the color vision mechanisms in perceptual grouping using tripole Glass patterns. A tripole Glass pattern consists of randomly-distributed groups of three dots, with one anchor dot and two context dots. The geometric relationship between any two dots defines the perceived global pattern. Observers may perceive either a clockwise (CW) or counter-clockwise (CCW) spiral if they can locally match the anchor dot with one or the other context dot, respectively. The chromaticity of the anchor dot was equally distributed on the equiluminant plane of a color space. One context dot had the same chromaticity as the anchor dot, while the other varied in chromaticity. The contrast of each context dot varied between one- to four-fold the detection threshold of the corresponding chromaticity. The observer was asked to judge whether the pattern was a CW or a CCW spiral. The probability of grouping the anchor dot with one context dot increased as a sigmoid-shaped function of the context dot contrast. The probability function shifted in a downward right direction as the contrast of the other context dot increased, suggesting a competition between the two ways of grouping. The probability of grouping the anchor and a context dot also decreased as the chromaticity difference between the two dots increased regardless of the anchor dot chromaticity. A divisive inhibition model with four pairs of color mechanisms explained the result. The tuning functions of two pairs of these mechanisms were similar to those of the cardinal equiluminant mechanisms. The other two pairs of mechanisms preferred some intermediate colors. We conclude that perceptual grouping involves extra color mechanisms than those found at the former stage of visual processing.