Describe and evaluate case studies into prosopagnosia Prosopagnosia is the inability to recognise faces that belong to people that they already know. The non-medical term for this is “Face Blindness”. There is two types of prosopagnosia. Acquired prosopagnosia, which is when prosopagnosia is gained as a result of brain damage but there were no previous signs of this disorder. Developmental prosopagnosia, which is developed from birth has an uncertain origin but may be due to a genetic component.
As prosopagnosia only effects face recognition it suggests that the Fusiform Face Area (FFA) is where the problem lies. This part of the brain relates to face recognition. It is thought that if this are of the brain is damaged it can lead to prosopagnosia.
Barton et al did a study in 2002 where he looked at 5 individuals with brain damage. He asked them to identify a series of different faces that he had altered (distance between eyes). Face recognition involves several different processes which are explained in Bruce and Young’s model of face recognition. One of the participants had a normal FFA whereas the FFA in the other four participants was damaged. Throughout the test, the participants whose FFA was normal performed normally in the test. The other four participants performed much more poorly. The conclusion of this was that ability to perceive changes of facial configuration was dependent on whether the FFA of the participant was damaged or not. This may lead to the failure of recognising faces (prosopagnosia).
This study had a very small sample number and therefore the population validity is low and we cannot generalise it to the rest of the world easily. The study also lacks ecological validity as the study used artificial stimulus which means that we are unable to generalise the findings to the rest of the world, this is because people are not used to having to recognise altered facial configuration in real life and therefore it may be a harder task for them to complete. Although the study does show support for the FFA being included in facial recognition, it doesn’t show that it is the only component nor that the FFA does not help in the recognition of other types of recognition. Such as the recognition of objects.
McNeil and Warrington did a case study in 2003 of a middle-aged man who had developed prosopagnosia as a result of a sudden drop in his blood pressure. They asked him to identify a picture of a famous person from a group of three pictures. The other two pictures were of unknown individuals. He was unable to select the famous one from the other two pictures. He then changed his career and became a sheep farmer. He was able to identify the differences between his sheep. This shows that his inability to recognise faces was only linked to human faces and that the recognition of animals and other objects was intact. The conclusion of this was that facial recognition is separate from the recognition of other objects or patterns.
This case study cannot be repeated as he was an individual and his injury would have been separate to him. Therefore we are unable to generalise the results of his study to the rest of the world as the conclusion of his case study may be individual to him but different for another person with prosopagnosia. However, the ecological validity of the study was higher as they did not use artificial stimuli so he would have been able to perform the task that he had to do without fault prior to his development of prosopagnosia.
Delvenne et al carried out a case study in 2003 on a 40 year old man who had suffered brain damage after being involved in a cycling accident. He developed severe visual agnosia for both objects and faces. If he was shown a simple, everyday object he tended to have difficulty in naming the object or stating the function of the object. However, he could tell the difference between an object and a face and could identify target faces from a group of ten photographs. He was also able to identify age and gender of a face but could not tell if the face he had identified was familiar or not and could not name people from a photograph. This suggests that object recognition and facial recognition use the same mechanisms. This case study also supports the Bruce and Young model of facial recognition as it suggests that facial speech analysis is a separate process in facial recognition as he could read facial expressions but he could not name faces.
The brain damaged that was suffered by the participant was individual to him and therefore the findings of his case study could not be generalised to the rest of the world. This is because the location of his brain damaged may not have only occurred in the FFA and therefore the cause of problems he was left with may have been related to brain damage in another area of the brain. As it was a case study, the sample number was a single individual and therefore the case study lacks population validity and cannot be generalised to the rest of the world. As the case study did not use artificial stimuli, the ecological validity would have been higher.