Single task、dual task、multi-task之比較

	Single task	Dual tasks	Multi-task
Advantage	l Easy to implement1	l Moderate level of difficulty to implement l Task complexity2 l Involve task switching3 l Involve inhibition4, 5 l More sensitive to cognitive status compared to the single task6 l Have additional attention distraction2 l Related to prefrontal cortical regions7 l Subfunctions ascribed to the central executive include dual-task processing8, 9 l Related to delayed intentions (prospective memory)	l Task complexity10 l Simultaneous multitaskingàcoordination of multiple factorsà predict complex community participationà increase ecological validity1, 10 l Everyday life is multitasking11 l Involve task switching3 l Related to delayed intentions (prospective memory)3
Disadvantage	l Not achieve complexity of executive functions12 l Real life is multitasking, not single task l Not test delayed intention (prospective memory) l Not involve inhibition	l Might have floor effect for testing individuals with intellectual disabilities8	l Too difficult to complete multi-task measure and high dropout rate10 l Floor effect

Dual task/multi-task之定義：個案在同一個狀況下接受到二個以上的任務，個案要決定哪個任務要先執行，然後執行另一個任務(記得執行下個任務[intention能力])。個案也可計畫如何要同時處理多個任務的某些部分，以節省時間，有效率地完成任務。意圖、決定/計畫、執行、有效率地完成，此四個要素，和Lezak model概念一致。

Single task和 dual task/multi-task之比較整理：
1. Single task之評估工具，病患較容易完成， dual task之評估工具，執行困難度為中度，病患仍然可能全部執行完成，但multi-task之評估工具，執行困難度較高，病患可以無法完成。
2. 雖然single task之評估工具容易完成，但真實生活為multi-task狀況，非single-task。所以single-task可能無法反應出真實執行狀況，和病患的真實實際的能力與問題。
3. 執行功能在測量個案在新奇(非例行的活動)、複雜性任務、非結構性的任務時的表現能力。single task的任務簡單，無法反應出個案在執行複雜任務時的能力。但dual task和multi-task的任務較複雜，所以可反應個案執行複雜任務時的能力。
4. 執行功能牽涉到"任務轉換(task switch)"的能力，在single-task中，不需在task中轉換，所以沒有真的測量到task switch。dual task和multi-task有二個以上的task，做完一個task後會轉換做另一個task，所以可評量到個案之task switch之能力。
5. Delayed intention (prospective memory)是指在執行二個以上的任務時，先執行第一個任務，然後在執行下一個任務，所以個案必須要記得接下來要做什麼(哪個任務)。然而在single task中無法測量此種能力，在dual task和multi-task中，可測量此種能力。
6. 執行功能牽涉"抑制(inhibition)"能力，個案在執行一個任務時，需要抑制自己不執行下一個任務(或被下一個任務所干擾[additional distraction])，此抑制能力必須在二個任務以上的狀況下發生。所以single task較無法評量inhibition能力，而dual task/multi-task可評量此能力。

Dual task和multi-task比較整理：
1. Dual task任務的困難度較低，所以對病患來說，較能完成任務，而較不容易產生floor effect或drop out的情況產生。另外，任務較少，所以可以較快完成，以節省評估的時間。
2. 雖說multi-task的任務為最複雜，可能較符合執行功能的定義，但過去研究中⁹，發現dual-task processing，可以區辨有執行功能正常和執行功能受損，此二個族群。所以dual task也可以使用測量執行功能能力。


Reference:

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9.         Baddeley A, Della Sala S, Papagno C, et al. Dual-task performance in dysexecutive and nondysexecutive patients with a frontal lesion. Neuropsychology 1997;11:187-194.

10.       Burgess PW, Alderman N, Forbes C, et al. The case for the development and use of "ecologically valid" measures of executive function in experimental and clinical neuropsychology. Jouranl of the International Neuropsychological Society 2006;12:194-209.

11.       Burgess PW. Strategy application disorder: the role of the frontal lobes in human multitasking. Psychological research 2000;63:279-288.

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