上而下控制在知覺決策上扮演相當重要的角色。然而，過去研究者皆透過參與者做完所有嘗試次後再做一個整體的口頭回報，進而推論參與者的決策歷程，如此無法反映參與者在每一題嘗試次判斷當下主觀的決策歷程。因此，本研究透過參與者及時的主觀報告，探討參與者是否有意識地察覺與控制知覺決策歷程。本研究利用系統多因子技術（Systems Factorial Technology, SFT），使用雙光點偵測作業，實驗一要求參與者在每一題嘗試次後，回報使用策略（平行或序列策略）；實驗二要求參與者於每一題嘗試次前，預先決定策略。結果發現在實驗一中，不論參與者回報使用序列或平行策略下，所有參與者皆採用平行自我終止或共同激發處理偵測目標；在實驗二中，不論參與者選擇使用平行或序列策略，所有參與者皆使用平行自我終止處理偵測目標。結果顯示參與者無法上而下控制使用序列處理偵測雙光點刺激。此結果可能與前注意處理階段不受上而下控制調控有關，且可用來反思上而下控制在知覺決策歷程上所扮演的角色。

Top-down control plays an important role in the selection of an optimal perceptual-decision strategy. However, in previous studies, inferences about the strategies have primarily been based on the participants’ subjective reports after they completed all experiments, which can not reflect their trial-by-trial strategies. Hence, this study investigated whether participants can be consciously aware of and control their strategies. A double-dot detection task was conducted and Systems Factorial Technology (SFT) was used for the experimental design, data analysis, and inferences. In Experiment 1, participants were asked to report their strategy (serial or parallel strategy) immediately after each trial; in Experiment 2, participants were asked to pre-select a strategy before a trial started. The results of Experiment 1 showed that all participants utilized either parallel self-terminating processing or coactive processing regardless of their reported strategies. Similarly, the results of Experiment 2 showed that all participants adopted parallel self-terminating processing regardless of their chosen strategies. These findings suggest that participants fail to intentionally adopt serial processing to detect redundant targets. Moreover, these outcomes occurred perhaps because pre-attentive processing is not affected by top-down control; accordingly, our results could further help understandings of how top-down control affects the perceptual decision process.