本研究的主要目的在於探討美沙冬的使用者是否具有抑制控制能力缺損、對海洛因相關刺激是否具有注意力偏誤，以及是否有彈性認知轉換能力上的問題。 研究使用的是Noel等人（2005,2007）發展出來的Go/No-Go作業，並使用海洛因圖片與中性圖片為作業刺激，分別測量受試者在作業中的反應正確率、反應遺漏數、反應犯錯數、平均反應時間、決定偏誤與區辨度，並且使用依賴嚴重度量表，以了解受試者對海洛因的依賴嚴重度與Go/No-Go作業各指標之間的相關。 　　美沙冬組樣本選取自八里療養院土城門診部之接受美沙冬治療者，共17人，經由網路招募之健康控制組十九人，受試者一共三十六人。共變數分析之結果顯示在Go/No-Go作業的正確率、遺漏數、區辨度和決定偏誤等指標上，發現組別與情境轉換之交互作用，顯示使用美沙冬之受試者具有彈性認知能力上的缺損，因此在有轉換的區段之中，無法快速地適應新的作答規則。此外，Go/No-Go作業結果未發現美沙冬使用者之抑制缺損與對海洛因相關圖片之注意力偏誤之現象。 　　依賴嚴重度與Go/No-Go作業的指標相關研究則發現，其依賴嚴重度越高，其在非轉換情境中對海洛圖片的犯錯數越低、決定偏誤越高，顯示美沙冬使用者似乎在沒有情境轉換的區段中，會將其注意力資源分配在海洛因圖片上，忽略非海洛因圖片，顯示其注意力較具選擇性。 / The goal of this study is to explore the inhibitory deficits、attentional bias towards heroin-related cues and cognition flexibility of current methadone users. The Go/No-go task used here was previously developed by Noel et al. (2005, 2007). Heroin-related pictures and neural pictures were presented as targets or non-targets. Accuracy rate、omission、commission、average reaction time、decision bias(C) and discrimination (d’) were being measured individually. The relation between the severity of heroin dependence and task performance was also investigated. The 17 subjects in methadone group were currently methadone maintenance treatment patients from Bali psychiatric center, and the 19 control group subjects without a drug using history were recruited by internet advertisement. The covariance analysis revealed interactions of group and shift/non-shift condition on accuracy rate、omission、decision bias(C) and discrimination (d’), indicating a cognitive flexibility deficits in methadone users. They had difficulty adapting to new rules in shifting conditions. No inhibitory deficits or attentional bias were found so far in this study. The relation between heroin dependence and Go/No-go task performance revealed that the more dependent the methadone subjects were, the less commission errors they made, the higher decision bias score they got towards heroin pictures in non-shifting conditions. It seemed that the methadone users were prone to allocate more attention resource to heroin-related pictures in non-shifting conditions, suggesting a more selective attention process.