連續性組織無論顯著與否皆可於視覺搜尋中遮蔽局部目標

Grouping in Good Continuity Can Mask a Local Target Regardless of Salience in Visual Search

視覺搜尋中，具有知覺群聚特性或顯眼的物體通常會獲取注意力，若目標位於顯眼的位置上亦應有益於搜尋。本實驗室先前的研究發現，在由許多小線段組成的搜尋畫面中，當目標與顯眼的干擾物重疊時，此干擾物若由彼此平行的線段組成（梯形干擾物）會促進搜尋，但若干擾物由彼此垂直的線段組成（蛇形干擾物）卻抑制搜尋。本研究欲探討促進和遮蔽效果與干擾物的知覺組織（相似性和連續性）和顯著性之間的關聯。實驗一將干擾物彎成曲線以去除干擾物組成內容的相似性，並打散背景線段的方位以降低干擾物的顯著性。結果發現蛇形干擾物仍產生遮蔽效果，但是梯形干擾物若在異質背景就失去其促進效果。實驗二進一步操弄蛇形曲線干擾物在異質背景中的旁側線段的方位（正交、平行與隨機），測試干擾物本身的顯眼程度是否會調控共線遮蔽效果的大小。結果發現，當蛇形干擾物旁側線段為正交方位時最顯眼，但是三種旁側情況皆有遮蔽效果且遮蔽效果的大小與干擾物顯眼程度無關。因此知覺組織連續性是共線遮蔽效果的充分條件，顯著性與相似性與共線遮蔽效果無關。本研究的結果可以應用在偽裝或擬態的設計上。

Salient or well-grouped stimuli usually capture attention. However, our previous studies showed a masking effect by a salient collinear distractor (i.e., snake) on a local target in visual search. Meanwhile, a salient non-collinear distractor (i.e., ladder) indeed facilitates search. The main difference between snake and ladder distractors was the grouping law good continuity. Nevertheless, the grouping law similarity and the saliency of the distractor can also affect search performance. This study aimed to test whether continuity is enough to elicit the collinear masking effect. Experiment 1 made the distractor curved to remove similarity of the items on the distractor, and randomized orientation in the background to reduce saliency of the distractor. Results showed that snake distractors impaired search regardless of similarity and saliency, while ladder distractors facilitated search only when background bars were homogeneous (i.e., when the distractors are salient). Experiment 2 manipulated the orientation of the flankers of the snake distractor to test whether distractor saliency modulated the size of collinear masking. Results showed that the orthogonal flankers make the distractor most salient; however, the size of the masking effect did not correlate to the degree of salience of the distractor. Our results suggest that items grouped in good continuity are sufficient to mask local targets in visual search, and the masking effect is irrelevant to the perceptual salience of the distractor. Our findings implicate possible applications on camouflage.