Introduction

Single dissociation

  • Definition：大脑某个结构A的受损会损害功能X而不会损害功能Y
  • Function/Aim：通过单分离，我们可以推断功能X和Y在某种程度上是相互独立的（X依赖A，而Y不依赖A）。
  • Example：Patient D.F. was unable to place a card in a slot, but could do so when told to place it “as if mailing a letter”. From this the conclusion was drawn that judging orientation is one ability (which D.F. had lost) and visual control of an action another (which D.F. could still do)(Bruce Goldstein, 2002).

    Bruce Goldstein: Sensation and Perception. Wadsworth, Pacific Grove (USA), 2002.

  • Limitations (by Josh de Leeuw). However, this kind of experiment wouldn’t be able to provide evidence that functions A and B are implemented in independent regions. To illustrate why, let’s consider the possible outcomes of the experiment:
    1. Functions A and B both remain in tact or Functions A and B are both disrupted. Clearly this outcome doesn’t provide any evidence that A and B are implemented in different regions, since both functions are affected equally by the lesion.
    2. Only function A is disrupted, function B remains in tact. The most that this outcome shows is that region X (the lesioned area) is crucial for function A but not B. However, what is doesn’t show is that function A is independent of function B. It could be the case that function A can be disrupted without disrupting function B, but that any disruption of function B will disrupt function A. One possible result of single dissociation

Double dissociation

Double dissociation

  • Definition. Double Dissociation is when two related mental processes are shown to function independently of each other.
  • Function/Aim. 通过双分离的方法，我们可以将不同心理过程所对应的脑区进行区分，证明不同心理过程在神经机制上是不同的（ two functions are neurologically distinct）。
  • History：最开始形成于图尔温一种解释内隐记忆的理论，用于解释健忘症病人记忆分离; 慢慢的成了内隐记忆的研究范式，; 国内华东师大杨治良最先最国内用这种范式。
  • Logic. 实验逻辑基于双分离原则（double dissociation），即你先控制单一的变量而比较在两种不 同的任务中变量的效应，如果变量影响被试在一种任务中的操作，但不影响另一种任务的操作，或者变量对两种任务的操作的影响有不同的方向，实验双分离就产生了。当然它包括了很多不同的实验设计，比如单一分离、交叉双重分离等等.
    认知神经实验验逻辑如下文举例：
    在脑功能定位中，有病人A、B，受损的脑部位不同，分别为X、Y。让两个病人都去执行a、b两种认知任务，若A完成了a而不能完成b，B完成了任务b而不能完成任务a，则X脑部与a认知功能相关，Y脑部与b认知功能相关（a依赖X，b依赖Y）。
    实验任务也不一定只有a、b两个，可以进行多个任务；被试也不一定只有两个，也可以有多个不同脑区受损的被试同时参与实验。
    为了展示双分离的效果，需要找到满足上述条件的大脑受损的病人。
  • Example. A classic example of Double Dissociation is speech and language comprehension. Although both processes pertain to use of language, the brain structures that control them work independently. When a part of the brain called the Broca’s area is damaged, patients may still understand language but be unable to speak fluently. They know what they want to say, but are unable to express themselves. On the other hand, when a part of the brain called Wernicke’s area is damaged, patients may still speak fluently, but be unable to comprehend language. This results in properly constructed but nonsensical sentences.

Empirical studies

参考资料

  1. https://psychology.stackexchange.com/questions/9690/what-is-the-difference-between-double-dissociation-and-simply-having-control-a
  2. https://en.wikipedia.org/wiki/Dissociation_(neuropsychology)
  3. https://psychology.stackexchange.com/questions/8199/what-does-double-dissociation-really-tell-us