So, looking through the case studies, we now can see that speech and non-speech sounds share a single early auditory processing mechanism (recall system A in Lichtheim’s model). However, then information separates and goes through different processing systems, dedicated specifically for speech and non-speech inputs. The model in full, then, could be shown as follows:
Where BOXES represent systems for processing or storing information, and ARROWS represent pathways of communication between the boxes. They do NOT alter information.
Let us look at the Bramwell's patient in relation to this model. What could go wrong with her, which box or arrow broke down?
She does understand all the sounds apart from human speech. Thus, the problem could lie in three possible places: arrow connecting Early Auditory Processing (EAP) box and Phonological Input Box (PIB), the PIM box itself or the arrow leading from PIB box to Semantic System box (SS).
She does understand all the sounds apart from human speech. Thus, the problem could lie in three possible places: arrow connecting Early Auditory Processing (EAP) box and Phonological Input Box (PIB), the PIM box itself or the arrow leading from PIB box to Semantic System box (SS).
Bramwell's patient
Now, consider this additional information about the patient; see if it will give more clues about where the problem lies.
1. Bramwell asked her: "Do you like Edinburgh?" She did not understand.
2. With signs, he asked her to repeat aloud his question ("Do you like Edinburgh?"). And she did so without hesitation!
3. He gave her a pen and a paper to write down what he (and then she) said. Again, she did! More importantly, she spelled it in a right way.
4. Only after writing it and reading it, she understood the question!
This test gives us a very important information. It shows that the speech input reaches that box and that the box itself is working fine, otherwise she would not be able to access this information to write it down. It leaves us with one possible answer: it is the arrow from PIB box to SS box which is broken, as she can not get to the words' semantic meaning when they come through her auditory input path - but only when she reads them.
1. Bramwell asked her: "Do you like Edinburgh?" She did not understand.
2. With signs, he asked her to repeat aloud his question ("Do you like Edinburgh?"). And she did so without hesitation!
3. He gave her a pen and a paper to write down what he (and then she) said. Again, she did! More importantly, she spelled it in a right way.
4. Only after writing it and reading it, she understood the question!
This test gives us a very important information. It shows that the speech input reaches that box and that the box itself is working fine, otherwise she would not be able to access this information to write it down. It leaves us with one possible answer: it is the arrow from PIB box to SS box which is broken, as she can not get to the words' semantic meaning when they come through her auditory input path - but only when she reads them.
So, there are three concepts which help to deal with the boxes (draw new ones, indicate the faulty ones etc.): Association, Dissociation and Double Dissociation.
We talk about association when several symptoms correlate; say, in Gerstmann's syndrome (1924), associated deficits are inability to tell one's fingers apart, to tell right from left, difficulties with writing and doing maths. However, this does not give us enough evidence to create a new, left-right-writing-number-finger module. Association merely indicates that these symptoms MAY occur together, however does not tell us whether they always occur together, or whether they could occur on their own too.
Dissociation is more useful in this case; Bramwell used it when he asked his patient to repeat and write down his question. Dissociation indicates that a patient is able to perform some tasks but not others; and so she could understand a written sentence but was unable to comprehend it when it was pronounced. This gives us evidence that these two tasks are being performed by different systems, thus we can draw a separate box.
However, sometimes dissociation might not really work. Imagine a patient who can perform task A but not B - does it necessarily mean that they are controlled by different brain areas? But what if task B is simply more difficult? You can quickly calculate 2+2, but might have difficulty working out (20986/36)*1/2* (875642) - but surely, it is no evidence for two separate modules: one for 'simple' and another one - for 'hard' maths!
Double Dissociation is the most reliable evidence; it occurs when we have two patients with opposite deficits, such as Broca's and Wernicke's ones. One of them could comprehend speech well but had difficulties producing it, while another one could talk fine but had troubles with comprehending. It assures us that these tasks are performed by separate systems, and so allows us to talk of separate boxes in a cognitive model.
We talk about association when several symptoms correlate; say, in Gerstmann's syndrome (1924), associated deficits are inability to tell one's fingers apart, to tell right from left, difficulties with writing and doing maths. However, this does not give us enough evidence to create a new, left-right-writing-number-finger module. Association merely indicates that these symptoms MAY occur together, however does not tell us whether they always occur together, or whether they could occur on their own too.
Dissociation is more useful in this case; Bramwell used it when he asked his patient to repeat and write down his question. Dissociation indicates that a patient is able to perform some tasks but not others; and so she could understand a written sentence but was unable to comprehend it when it was pronounced. This gives us evidence that these two tasks are being performed by different systems, thus we can draw a separate box.
However, sometimes dissociation might not really work. Imagine a patient who can perform task A but not B - does it necessarily mean that they are controlled by different brain areas? But what if task B is simply more difficult? You can quickly calculate 2+2, but might have difficulty working out (20986/36)*1/2* (875642) - but surely, it is no evidence for two separate modules: one for 'simple' and another one - for 'hard' maths!
Double Dissociation is the most reliable evidence; it occurs when we have two patients with opposite deficits, such as Broca's and Wernicke's ones. One of them could comprehend speech well but had difficulties producing it, while another one could talk fine but had troubles with comprehending. It assures us that these tasks are performed by separate systems, and so allows us to talk of separate boxes in a cognitive model.