目標與非目標物競爭對視覺搜尋中選擇性注意力影響的神經證據

Abstract

由於人類的視覺注意力資源有限，僅有少數物件能夠被處理。因此當目標與非目標物同時出現時，雙方就必須競爭資源，且越相似的物件對目標物的競爭就越強。然而，目標物與非目標物間的競爭如何影響視覺搜尋當中的選擇性注意力與選擇性注意力相關神經指標的神經來源仍不清楚。本論文藉由操弄目標與非目標物相似性並分別採用腦電波與腦磁波觀測兩個與選擇性注意力相關的神經指標：(1)N2pc效果，反應視覺搜尋中的空間注意力選擇; (2) alpha側化效果，反應目標物的選擇與非目標物的抑制，以及探討大腦有效性連結來釐清此研究問題。結果顯示，在高競爭時，alpha側化效果首先發生，接續出現的為N2pc效應（280 ms），隨後再次出現alpha側化效果，而此效果是來自對側訊號降低引起，反映了目標物選擇。低相競爭時，N2pc 效果（200 ms）首先出現，然後是 alpha 側化效果，此效果來自於同側訊號增加引起，反映了非目標抑制。我發現事件相關磁場之間具有有效性連結性並會隨時間而改變連結狀態，且在低競爭和高競爭時連結也有所不同。此外，alpha側化效果的結果發現，反應目標物選擇的alpha側化效果源自頂葉，而反應非目標物抑制的alpha側化效果則源自顳葉。另外，我以跨顱交流電技術來研究來探索 alpha 側化效果和視覺搜尋表現之間的因果關係，但我沒有找到因果關係。令人驚訝的是，我發現了個體alpha波頻率頂點可以預測視覺搜尋表現。本論文提供了實證證據，顯示視覺搜尋中的選擇性注意受到目標與非物標物間的競爭影響會以不同的方式運作。

Visual search is highly relevant in people’s daily life. Because the attention of people is limited, only a few items can be processed. The nontargets compete for processing with the target. The high similarity of items causes stronger competition between them. However, little is known about when and how target-nontarget (T-N) competition influences selective attention in visual search and where the neural origins of neural correlates of selective attention are. I addressed these questions by manipulating T-N similarity, assessing two neural correlates of selective attention using electroencephalography (EEG) and magnetoencephalography (MEG): (1) the N2pc effect, reflecting spatial selection in visual search; (2) the alpha lateralized effect, reflecting target prioritization and nontarget suppression. Also, I explored the effective connectivity of brain areas. The results showed that for high similarity, the alpha lateralized effect occurred first, then the late N2pc effect (280 msec) followed, and the N2pc was followed by the alpha lateralized effect. The alpha effect was caused by decreasing power on the contralateral side and reflected target selection. For low similarity, the early N2pc effect occurred (200 ms), followed by the alpha lateralized effect. The alpha effect was caused by increasing power on the ipsilateral side and reflected nontarget suppression. I found that the effective connections changed through time and difference between low and high T-N similarity conditions. Furthermore, the results of the alpha lateralized effect showed that the alpha lateralized effect which reflected target selection originated from the parietal cortex, and the effect which reflected distractor suppression originated from the temporal cortex. A tACS study was also conducted to explore the causal relationship between the alpha lateralized effect and search performance, but I did not find a causal relationship between the alpha lateralized effect and search performance. Surprisingly, I found that PIAF can predict search performance. In summary, this dissertation provides empirical evidence to show that selective attention in visual search operates in different ways, depending on the competitive level.