What is a double dissociation? Give an example? What can we learn about the brain from double dissociations?

What is a double dissociation? Give an example? What can we learn about the brain from double dissociations?

Studies of patients have established a double dissociation between STM and LTM. That is, there are some patients with functioning STM who can't form a new memories, or the other way- there are patients who have poor STM but functioning LTM. Taken together, these two types of patients establish a double dissociation.

An example of a person with double dissociation can be a musican Clive Wearing. He lost his memory as a result of viral encephaltis. He has functioning STM, but is unable to form new memories in LTM.

A double dissociation indicates, that STM and LTM operate independently and are served by different mechanism.

A double dissociation usually refers to two cognitive faculties that are believed to be linked in some way where each can receive damage whilst the other remains intact and functioning.

The best example for this is memory. It is possible for long term memory (LTM) to become damaged and short term memory (STM) to remain intact. This would be a dissociation and is not surprising as most memories in LTM have been consciously processed in STM. However, it has also been found that STM can be damaged yet LTM remains intact. Thus there is a double dissociation between LTM and STM. Evidence for this double dissociation has been found in people with anterograde amnesia (those who are unable to form new memories and have damaged STM) as they are still able to learn new skills despite having no memory of being taught them.It must also be said though that for many double dissociations in cognitive neuropsychology there is very nearly always some degree of loss of function in the faculty that remains intact. It's quite rare in a double dissociation for one to remain perfect and the other to be destroyed.

Double dissociation is the case in which an activity or variable affects one process but not another and a second activity or variable has the reverse effects.

As mentioned by Kamil above, Clive Wearing could be an example of this but also double dissociation within language e.g. Aphasia. Suggests that two language aphasia are separable and can occur independently of each other

We can talk about a double dissociation when two related mental processes are shown to function independently from each other. It allows scientists to see which specific areas of the brain are responsible for specific mental processes.

A good example of double dissociation may be seen in speach and language comprehension which are similar mental processes, happening in different areas of the brain, independent of each other. This was proven when looking at impairments of two brain areas - the Broca's area and the Wernicke's area. The patients having damage to the first one may still understand language but be unable to speak it fulently as even though they know what they wish to say they cannot express it in words fluently. Pateints with damage to the second one - Wernicke's area, may be able to speak fluently however may not comprehend language, which results in good construction of sentences which do not have a lot of sense.

The different type of memory loss is in fact a good example of double dissociation however the case of Clive Wearing is in my opinion not the best case to show it. Clive Wearing has lost both his long term memory and short term memory and only his procedural memory has stayed intact. When considering this last fact we can infact state that a double dissociation exists, however in the case of long term memory and short term memory it is not so.