完形心理學連續律與相似律之內在機制探討

LOCAL ENHANCING CONNECTIONS AMONG SPATIAL FREQUENCY FILTERS MIGHT MEDIATE GESTALT GROUPING PRINCIPLES

本研究採用背景刺激對於一個目標刺激所產生的脈絡效果來探討連續律及相似律的內在機制。當一群Gabor的局部方向角與其整體排列的路徑一致時，對其構成成員之一的Gabor偵測閾會明顯地低於該Gabor單獨存在時的偵測閾，而且無論這群Gabor的排列方式是直線或曲線構型均然，顯見視覺濾器之間具有促進性的聯結，而且此聯結的方式符合Field，Hayes與Hess（1993）的局部聯結場理論之預測。單純的機率加成效果並不能解釋我們於實驗中觀察到的閾限下降現象，然而背景刺激對於目標刺激的脈絡效果與前者的對比值有關，在極弱的對比時，背景對目標刺激具穩定的促進效果，然而在對比較強的情況下，此促進效果便消失，甚或有轉為抑制作用的趨勢。此結果與對V1區域細胞間遠距連結的電生理研究一致，但與Polat和Sagi（1993; 1994a.b）的結果有衝突。我們亦發現只要一群Gabor的局部方向角皆相同時，不管成員方向角與位置是否符合局部聯結場定義下的有效構型，亦可觀察到背景對目標的促進效果，此現象可能是相似律的內在機制。整體而言，本研究的結果傾向於支持群聚（grouping）現象是視覺濾器間的局部促進連結的作用結果，似乎不需牽涉更高層次的集合單位（collators）。

There has been a revived interest in understanding the internal mechanisms underlying Gestalt principles in both neural physiological and visual psychophysical studies in recent years. It has been shown that perceptually, a group of Gabor elements with locally aligned orientations pops out from a background comprising the same Gabors with random orientations. A local association field (LAF, Field, Hayes & Hess, 1993) around each VI filter working at suprathreshold contrast levels was proposed to account for the orientation-dependent grouping effect. We aimed to investigate whether LAF can be understood as mutual enhancing connections among V 1 filters. We have found a substantial reduction in the detection threshold of a Gabor patch presented in a match-to-LAP configuration as compared to that in a non-match condition. Probability summation cannot account for the magnitude of such reduction. We have also obtained results inconsistent with the LAF model. Specifically, when the orientations of the three Gabors in a triplet were all the same, a substantial threshold reduction was also found, even when the triplet was in an invalid configuration. While such results are at odds with the LAF model, they are consistent with the law of similarity proposed by the Gestalt psychologists. It thus appears that there are excitatory connections both between filters of the same orientation preferences, regardless of their relative cortical positions, and between filters arranged in a manner that matches the LAF configurations.