共線遮蔽效果在視覺搜尋上的時間特性

Temporal Characteristics of the Collinear Masking Effect in Visual Search

在視覺搜尋中一個顯著的目標通常比較容易被找到。然而，我們之前的研究發現共線知覺組織可以扭轉這個現象，稱為共線遮蔽效果。該實驗呈現一個由一行行水平白色小線段依序排列的搜尋畫面，其中一行是由垂直的小線段排列而成，造成顯著且組織良好的共線干擾物。參與者的作業是判斷一個傾斜的小缺口（目標）是左斜還是右斜。共線遮蔽效果是指當目標出現在共線干擾物那一行時，反應時間會比目標在背景上還慢。由於顯著的特徵影響視覺搜尋是在比較早（例如40到70毫秒）的訊息處理階段，而特徵結合或輪廓處理則是相對而言比較晚的時間（例如150到300毫秒），故本篇測試這些時間點內共線遮蔽效果是否會發生。我們嘗試用不同的遮蔽物，發現共線遮蔽效果在參與者可以辨識目標的同時即可發生。若先呈現搜尋畫面，目標之後才呈現，則搜尋畫面只需呈現40毫秒就可以觀察到共線遮蔽效果。綜合而言，我們認為共線遮蔽效果可以發生在訊息呈現的40到70毫秒內。此結果顯示共線遮蔽效果發生在與顯著性計算一樣早的時間點，也顯示出共線的組織特性在非常早的訊息處理階段即干擾了視覺搜尋表現。

A salient target is usually easier to find in visual search. However, perceptual grouping, collinearity in particular, can reverse this observation. The phenomenon, called the collinear masking effect, was observed for a search display that was filled with horizontal bars while a column of bars were vertical (the collinear column). This collinear column thus is salient and well-grouped. The task was to discriminate a small oriented bar either in the collinear column or in other columns in the background. The collinear masking effect refers to the phenomenon that discrimination was slower for a target on the collinear column comparing to that in the background. Since feature saliency affect visual search in relatively early (e.g., 40 to 70 ms) while feature conjunctions late (e.g., 150 to 300 ms) in information process stages, we examined the time course of the collinear masking effect in this study. With limited presentation durations (40, 70, 150, or 300 ms), different masks lead to different results. Nevertheless, the collinear masking effect was observed at the time point when the target discrimination was above chance level. Further experiment showed that if the search display was presented preceded the target, reliable collinear masking effect was obtained as early as 40 ms. We thus concluded that the collinear masking effect can be found in 40 to 70 ms. Our results imply that the collinear masking effect occurred as fast as saliency was calculated, suggesting that collinear grouping interferes with visual search very early in the information processing stream.