什麼是「執行困難」？(Hughes, Russell, & Robins, 1994)

最簡單來說，是不能從目前的處境中抽離，也不能跟隨個人的思考模式來行動。在想法解讀 (Theory of Mind) 的錯誤想法 (false belief) 測試中，它指知覺上不能擺脫物件在當眼位置的影響，因而選擇了一個最明顯但也是錯的答案。

 

什麼和執行職能 (executive functioning) 有關？

目前對執行職能所包括的能力並無定論，一般認為應有下列：

1.          組成抽象概念；

2.          訂立具彈性的行動方案；

3.          維持集中的注意力和思考力；

4.          快速地抽取有關資料；

5.          進行某項工作當中的自我監控和修正；

6.          抑制衝動的反應。

 

參考Hughes & Russell (1993) 的測試內容，可有更好的了解：

小窗測試

在這項測試中，小孩可從一個小窗觀看兩個箱子的內部，他需要指向他挑選的那個箱子。假如他指向那個沒有放糖的箱子，就可贏得一粒糖。如他指向有糖的箱子，就不會有糖的獎賞。另一種測試是加進一位對手，對手會打開小孩曾經指向的箱子，如果裡面有糖，就歸對手所有。這項測試的關鍵是要小孩騙倒對手，他方可得到獎賞。測試結果顯示自閉症兒童不管有沒有對手，他的成績都很差。

 (以上見於Happ F. (1994). Autism. Massachusetts: Harvard University Press P.54)

 

威斯康辛卡片分類測試 - 「執行困難」理論的最有力測試

這項測試目的是量度接受測試人士隨口頭指示改變分類基準的靈活性。先讓接受測試人士看4張分為不同顏色、外形、或號碼的卡片，然後請他開始為128張卡片分類。測試員不會告訴他怎樣分，只在他每疊好一張卡片後告訴他做得正確不正確。他對10張卡片後，測試員會告訴他改用另一種分類基準，如此類推，直至疊完128張卡片為止。這個測試統計三項分數：

1.          完成分類的數目；

2.          正確的分類卡數；

3.          因為用上一個分類基準而錯誤的卡片數目。

自閉症人士的第三項分數比一般人都低。

(Heaton, Chelune, Talley, Kay, & Curtis, 1993)

 

學者 (Fein, D. et.al. Executive Functioning in High-functioning Children with autism. Journal of Child Psychology and Psychiatry Vol.42, Bo.2, pp.261-270, 2001) 對「執行困難」理論的研究結果：

1.          自閉症人士只有某些執行職能受損，最明顯的是重覆地犯同樣的錯誤，在一些困難的作業尤其常見。自閉症人士特別傾向於知道錯還是繼續錯下去，遇到困難的作業，很難改變思考模式。

2.          計劃能力有問題。「執行困難」與重覆犯錯不清楚是否存在因果關係，也許重覆犯錯反映了自閉症的基本問題。

 

「執行困難」與前額葉受損的關係

(以下見於Ozonoff, S. (1995) Executive Functions in Autism. Learning and Cognition in Autism. New York: Plenum Press)

 

腦前額葉受傷病人的表現：

1.          重複、無意義的行為或說話；

2.          難以抑制某些熟習或易有的反應；

3.          不適當地重複某些舊的想法或行動；

4.          編訂計劃能力不足；

5.          在處理資料方面，只注意資料的某個單一部分、或難以合零星資料、或不能同時兼顧來自不同渠道的資料、或不能適當地運用已知的資料。

 

自閉症人士相似的行為：

1.          僵化、欠缺彈性的行為；

2.          因環境的輕微改變而感到不安；

3.          堅持完全遵循慣例的每個細節；

4.          只對某偏狹嗜好有興趣或不停重複某個刻板的行為；

5.          行為衝動、難以抑制即時的反應；

6.          難以運用大量儲存的資料；

7.          只能針對細節而不顧及整體。

 

腦前額葉包括的能力：

1.          構思一個想法 (如計劃、大綱、反應模式)，並用之來完成某項工作。在一個策略不適用時，可以轉換其他反應模式；

2.          調校社交行為、情緒反應和社交談話。

由於後者，腦前額葉受損因而可解釋自閉症社交方面的障礙。

 

以腦前額葉受損解釋自閉症的局限：

1.          為什麼前額葉早期受損的兒童沒有自閉症？前額葉功能不足只是一個必須條件，而不是造成自閉症的充分條件，加入了其他認知的障礙或神經的功能不足才會引發自閉症的徵狀。

2.          有些由想法指導行動的能力，見於譬如‘物件恆在’ (object permanence: Morgan, Cutrer, Coplin, & Rodrigue, 1989)‘錯的照片’(false photographs tasks: Leslie & Thaiss, 1992) 等等測試，測試員以為它們會因前額葉受損而受到影響 可是並不如此。

3.          因前額葉引致的認知能力受損，也見於過度活躍症，行為失調問題等。執行困難障礙和自閉症究竟有什麼特別的關連？

 

「執行困難」理論的內容有很多爭議性的地方，如

l          有自閉症人士並無抑制能力方面的問題；

l          有自閉症人士並無短期記憶 (working memory) 的問題；

l          有自閉症人士並非不明白曾經存在的事物 (比對目前的現實較不明顯)；

l          「執行困難」理論作為失調症的界準不夠明顯，因其他如過度活躍症、精神分裂、妄想強迫症也有這問題；

l          它始終不足以解釋社交障礙不存在其他有執行困難問題的失調症而只存在於自閉症。

 

學者Simon Baron-Cohen 對「執行困難」理論的意見

Baron-Cohen, S. (draft 4th May 2001). The exact mind: Empathising and systemizing in autism spectrum conditions? To appear in Goswami, U, (ed) Handbook of Cognitive Development. Blackwell:Oxford (in press)

 

直至目前為止，從認知角度去解釋自閉症的重複性行為、喜歡遵循慣例與堅持一成不變等習性，只有「執行困難」理論。(Ozonoff, Rogers, Farnham & Pennington, 1994; Pennington et al., 1997: Russell, 1997b)

雖然「執行困難」理論有可能導致刻板行為，但也有亞士保加症 (Asperger Syndrome)人士並無執行困難徵狀，他們對系統有良好的概念，卻在感情代入方面能力不足。由此可見，「執行困難」不可能是自閉症的主要徵狀。

「執行困難」理論亦向來忽略了重複性行為的內容。相對來說，感情代入(empathizing)/系統建立(systemizing)理論卻指出自閉症兒童對機械或其他系統的沉迷，是基於它們擁有一些可知的規律，它可能顯示自閉症兒童完整甚或發展良好的普通物理常識。



Executive Functioning

以下採自Fein, D. et.al.(2001) Executive Functioning in High-functioning Children with autism. Journal of Child Psychology and Psychiatry Vol.42, Bo.2, pp.261-270, 2001

Autistic disorder and other pervasive developmental disorders are generally associated with weaknesses on tasks involving cognitive flexibility, verbal reasoning, complex or verbal memory, and complex language. It has been proposed, accordingly, that cognitive deficits, specifically executive functioning deficits, are a primary cause of autistic behavior (Ozonoff, Pennington, & Rogers, 1991; Pennington et al., 1997: Russell, 1997)

 

What is Executive Functioning (EF) or Executive Dysfunction?

Although there is no consensus about the components of executive functioning, it is thought to include such processes as

-         forming abstract concepts,

-         having a flexible sequenced plan of action,

-         focusing and sustaining attention and mental effort,

-         rapidly retrieving relevant information

-         being able to self-monitor and self-correct as a task is performed

-         being able to inhibit impulsive responses

Executive functioning can also be described as the ability to disengage from the current situation and guide behavior by referring to mental models (Hughes, Russell, & Robins, 1994)

最簡單來說，是不能將自己從某些物件脫離，在ToM的錯誤想法(false belief)測試中，它指知覺上不能擺脫物件在實際位置的明顯性，因而選擇了一個最明顯但也是錯的答案。

參考Hughes & Russell (1993) 的測試內容，可有更好的了解：

“windows task”

In this task the child simply had to point to one of two boxes, into which he/she alone could see via a small window. On each trial a sweet was placed in one of the boxes, and if the child indicated the empty box(versus the second, baited box), he won the sweet. In the competitor version, an ignorant second player searched in the indicated box, and kept any sweets thus found – so that the child was effectively rewarded for “deceiving” the competitor.

It was found that autistic subjects did badly at the “windows task’ with or without a competitor.

(以上見於Happ F. (1994). Autism. Massachusetts: Harvard University Press P.54)

 

The most Robust Test in EF – Wisconsin card Sorting Test (WCST) and what is it?

This test involves the ability to change sorting categories flexibly in response to verbal feedback. Subjects are shown 4 cards that vary on three dimensions (color, form, and number). They are then told that they must sort a stack of 128 cards but are not told how to sort them. They must respond to examiner feedback (they are told correct or incorrect after each trial). After a subject sorts 10 cards correctly, the sorting principle changes (from color to form to number). Several scores are calculated during this test. Total categories indicates the total number of complete sorting categories achieved (the maximum is 6). Total number correct indicates how many correct cards were sorted. Number of perseverative errors indicates how many times the subject sorted to a previously reinforced category, thus ignoring the negative feedback.

(Heaton, Chelune, Talley, Kay, & Curtis, 1993)

 

Temple Grandin’s explanation of ‘Perseveration’ (1995):

People with autism may be using a different selective attention mechanism than normal people (Ciesielski, Courchesne, & Elmasian, 1990) Their research has shown that people with autism take much longer to shift between visual and auditory stimuli. Attention shifting may explain some socially inappropriate behavior. Donna Williams explained that it is difficult to look for social rules in her memory at the moment an event is occurring. In some cases, perseveration may be an extreme dysfunction of attention shifting.

 

Findings of Fein’s paper:

1.      Only certain executive functions are affected in autism, most notably perseveration (知道錯但繼續錯下去). Perseveration occurs most often on tasks of greater difficulty. Individuals with autism tend to make perseverative errors and have difficulty changing cognitive set on challenging tasks.

2.      There are deficits on planning tasks.

It is unclear whether the relationship between EF and perseverative behavior is causal or whether perserveration is a reflection of how autism was defined in the first place.

 

Relationship between Executive Dysfunction and Frontal Lesion

(以下見於Ozonoff, S. (1995) Executive Functions in Autism. Learning and Cognition in Autism. New York: Plenum Press)

腦前額葉受傷病人的表現：

The deficits incurred have been richly described by Luria (1966) and more recently, by Duncan (1986) and Stuss and Benson (1986); they include

l          Repetitive, aimless movements or speech

l          Difficulty inhibiting familiar or obvious responses

l          Inappropriate repetition of previous thoughts or actions

l          Diminished capacity for planning

Stuss (1987,cited in Mateer 7 Williams, 1991) described several additional information-processing deficits :

l          A tendency to focus on one aspect of information

l          Difficulty relating or integrating isolated details

l          Problems managing simultaneous or multiple sources of information

l          Impaired ability to act on or apply knowledge in a meaningful manner

 

自閉症人士相似的行為：

l          rigid and inflexible behavior

l          becoming distressed over trivial changes in the environment

l          insistence on following routines in precise detail

l          focusing on one narrow interest or repetitively engaging in one stereotyped behavior

l          impulsiveness, having trouble delaying or inhibiting responses

l          having trouble applying or using their large store of knowledge

l          focusing on details and having difficulty in seeing the big picture

 

腦前額葉包括的能力：

l          the ability to form a mental representation (e.g. a plan, schema or response set) that must be held on-line to successfully complete the task and flexibility in shifting response set when a strategy is no longer correct

l          regulation of social behavior, emotional reactions (Stuss & Benson, 1986) and social discourse (Dennis, 1991)

由於後者，腦前額葉受傷因而可解釋自閉症社交方面的障礙。

 

以腦前額葉受傷解釋自閉症的局限：

1.Why do children with early frontal lesions not appear autistic?

Prefrontal dysfunction may be a necessary, but not a sufficient, criterion for the development of autism; perhaps other cognitive deficits, or neurological dysfunction, must also be present to produce the full-blown syndrome.

 

2. There are some abilities that a deficit in using mental representations to guide behaviors would predict to be impaired are in actual circumstances not impaired, e.g. object permanence (Morgan, Cutrer, Coplin, & Rodrigue, 1989); false photograph tasks (Leslie & thaiss, 1992) Is it because they rely on external clues or these tasks are not highly abstract or novel? Thus, a number of factors may be important in determining whether individuals with autism can use internal models, rather than external context, to guide behavior.

 

3. frontal lobe cognitive dysfunction is not specific to autism, also seen in ADHD, conduct disorder etc. The question is : how executive function deficits might be related to autism in a way that differentiates it from other disorders.

 

EF的理論內容有很多爭議性的地方，如

-         有自閉症人士並無inhibition 的問題

-         有自閉症人士並無working memory 的問題

-         有自閉症人士並非不明白曾經存在的事物 (比對目前的現實較不明顯)

-         EF作為失調症的界定性不夠明顯，因其他如ADHD, 精神分裂, obsessive-compulsive disorder 也有這問題

-         Bishop (1993) : It is insufficient to account for documented deficits in social cognition, because such deficits are not shown by other clinical groups with impaired executive system functions, and because autistic children fail to show comparable difficulty when second-order representations do not involve social material.

 

What does Simon Baron-Cohen say about EF?

Baron-Cohen, S. (draft 4th May 2001). The exact mind: Empathising and systemizing in autism spectrum conditions? To appear in Goswami, U, (ed) Handbook of Cognitive Development. Blackwell:Oxford (in press)

 

To date, the only cognitive account to attempt to explain “repetitive behavior”, a strong desire for routines, and a “need for sameness” is the executive dysfunction theory (Ozonoff, Rogers, Farnham & Pennington, 1994; Pennington et al., 1997: Russell, 1997b)

While ‘stereotypies’ are likely to be due to executive deficits, the fact that it is possible for people with Asperger Syndrome to exist who have no demonstrable executive dysfunction whilst still have deficits in empathizing and talents in systemizing suggests that executive dysfunction cannot be a core feature of autism spectrum conditions.

The executive account has also traditionally ignored the content of “repetitive behavior”. The empathizing-systemising theory in contrast draws attention to the fact that much repetitive behavior involves the child’s ‘obsessional’ or strong interests with mechanical systems or other systems that can be understood in terms of rules and regularities. This may reflect the child’s intact or even superior development of their folk physics.