Are Faces Special free essay sample

Critically evaluate the evidence that we have evolved a specialised neural network dedicated to processing faces. Brian Marron, 11461992, SF TSM. INTRODUCTION Processing faces is extremely important to humans as social beings. We are able to put and identity on thousands of faces (Gazzaniga, 2002) with ease, something we might take for granted. The value of this ability can be better understood when the world is viewed through the eyes of somebody with prosopagnosia, the inability to recognise faces. The following quotation from David Fine, a prosopagnosic describing the difficulty associated with the disorder. â€Å"I often fail to recognise my children or even my wife †¦ I have failed to acknowledge friends and, more distressingly, those in authority. At school I would get lines for not raising my cap to a teacher. As a young man I ignored girls whom I had met the night before – not a good mating strategy. I find networking all but impossible, and social situations †¦ may cause acute anxiety. † (Fine, J. R. 2011 pp 455) Face processing is something that almost all of us can do yet exactly how we process faces is not yet known. In this essay I will examine one of the most heatedly debated topics of face processing: Are faces special? That is to say, are faces processed in a special way compared to non-face stimuli and have humans evolved a specialised neural network to achieve this? The two sides of the argument have been debated for a long time and there is still no clear answer. (Hole Byrne, 2010) Research from both sides will be critically evaluated. Initially, evidence from psychological studies will be explored in an attempt to address whether faces are processed in the same way as non-face stimuli. After that the question of whether humans have evolved a specialised network dedicated to processing faces will be considered, drawing on evidence from studies of brain damage and neuroimaging. If faces and only were processed in a different way to non-face stimuli, it would greatly support the argument that faces are special. Yin carried out a very influential experiment in 1969. He presented participants with photos of faces, stickmen drawings, planes and houses. The task involved participants recognizing the stimuli presented inverted or â€Å"right-way-up†. Yin found that inversion decreased people’s ability to recognise all categories of stimulus. However, inversion impeded performance by 3 times as much for faces compared with other non-face stimuli. Yin also collected oral feedback. The results and feedback suggested that faces and non-face stimuli were processed differently. After many more very influential studies, such as the Thatcher Illusion (Thompson, 1980), the Composite Face Effect (Young et al. 1987), blurring facial features (Collinshaw and Hole, 2000) and many more, it was concluded that faces were processed in a different way to non-face stimuli. Specifically, faces are processed holistically with a dependence on configural information whereas non-face stimuli are processed using featural information in a peicemental way. It was concluded that because faces were processed differently they are special. Diamond and Carey disagreed (1986) that face and non-face stimuli were processed differently faces were special. They put forward the expertise hypothesis in a much cited paper in 1986. They said the Face Inversion Effect found by Yin was not a result of using different sources of information (configural and featural) but that it was a result of expertise with faces. They based their assertions on evidence from their experiment with dog experts. Dog experts and non-experts were given a similar inversion test to Yin’s, with photos of dogs as well as faces (1969). Again they were asked to recognise the dogs and human faces while upright or inverted. Understandably, Yin’s Inversion Effect was found for faces. Interestingly, the dog experts showed a similar inversion effect for dogs while the non-experts did not. It seemed the experts processed faces and dogs in a similar way. Diamond and Carey argued that if one is expert in any group of homogeneous stimuli whose members all share features, then one begins to use configural information to improve discrimination of its exemplars. They also said that to allow for this better discrimination, the stimulus must be presented upright. People demonstrate the Face Inversion Effect because they are expert at processing faces. And so, Diamond and Carey asserted faces are not special, merely exemplars of a homogenous group of stimuli of which people tend to be expert. Greebles were created by Gauthier and Tarr (1997) from a need to control for expertise in experiments. Greebles are a group of homogeneous stimuli that do not resemble faces but do have several properties of faces like symmetry and the same number of features. They conducted experiments to see how dependence on configural information increased with expertise. They agreed with Diamond and Carey that faces are not intrinsically special but that humans are particularly expert at processing faces and so rely more on configural information to discriminate b etween one person and another. However, Gauthier Tarr and Diamond Carey’s methodologies have come under much criticism especially from Robbins and McKone. Robbins and McKone argue that they have found major flaws in the expert hypothesis. The differing views of these psychologists are outlined in fiery academic exchanges (Robbins McKone 2007), (McKone Robbins, 2007), (Gauthier Baukach, 2007). As a consequence, there is no absolute answer to the question: Are faces special? The next line of evidence is brain damage. The logic is this: if a brain region is damaged and face processing is hindered with all other non-face processing remaining unhindered, then surely that is strong evidence for a specialised neural network dedicated to processing faces only. Hole Byrne, 2010) i. e. A double-dissociation must be shown between face and non-face stimuli. Prosopagnosia patients are the most promising hopes for meeting those criteria just outlined (Gazzaniga, 2002). It is seldom that a prosopagnosia patient does not show impairments to non-face-stimulus processing abilities. This is thought to be because traumatic brain injuries resulting in prosopagnosia are usually wide-ranging (Farah et al, 1995). However, there are some cases of ‘pure’ prosopagnosia who have no non-face processing impairments (Wada Yamatoto, 2001). For the evidence to be valid, they must make within-class discriminations to make the test comparable with face processing tests. This within-class double dissociation has been found in many object classes like cars (Rossion et al, 2003), glasses (Farah et al, 1995) fruit (Riddoch et al, 2008) and more. There is even evidence for a double dissociation between human and animal face-processing. There is the case of a sheep farmer, WJ (McNeil Warrington, 1993). WJ suffered from prosopagnosia yet he was able to identify his sheep. Another case of a prosopagnosic farmer being able to identify his animals was reported by Bruyer et al. 1983). The double dissociation is made whole by a farmer who could process faces but could sadly no longer identify his cattle. The evidence to show faces are indeed special is compelling. However, there is an alternative explanation of the findings provided by the expert hypothesis. According to that hypothesis, in order to recognise faces we must make deli cate within-class decisions on the second-order relations between facial features. Supporters of the hypothesis argue that prosopagnosia is not the injury of the ‘face’ area but injury to the region responsible for making delicate within-class decisions. When asked why faces are selectively impaired, it is argued that it only appears that way because brains depend on that mode of processing to a great extent for faces (Hole Byrne, 2010). Consequently, there is still no definite answer to the question of whether faces are special. The most modern evidence comes from neuroimaging. The N170 ERP was instrumental in highlighting brain activation when viewing face stimuli. The activation patterns helped to locate the fusiform face area (FFA) because N170 was so distinct to faces. In this essay the fMRI research into the FFA will be explored in detail. To prove faces are special, the research aimed to find a correlation between distinct face-processing brain activity and a specific brain region. The FFA was discovered in 1997 by Kanwisher. It was first described as a brain region which only responded to faces. In fact, activation was found for cat faces and cartoon faces (Tong et al, 2000). There was also some very low level activation to animals, houses and objects. Interestingly, FFA activation was recorded in response to Mooney faces, (Kanwisher, 1998) and to the vase-face illusion. When participants reported perceiving a vase there was no FFA activation. Activation only occurred when perceived as 2 faces looking at each other. This finding was very meaningful as in both vase-face scenarios the stimulus was the same. The only thing change was the perception (Andrews et al, 2002). It supports the assertion that faces are special and humans have evolved a special neural network dedicated to processing faces. The expertise hypothesis does not accept those findings. Supporters argue that the FFA is for detecting subtle differences in stimuli (Gauthier et, al, 1999). Evidence for this can be found in Gauthier’s experiment with bird watchers (2000). FFA activation was found to be higher in experts than non-experts. Further evidence in support of the expertise hypothesis is that FFA activation is usually higher for one’s own race (Golby et al, 2001). This is significant because the expertise hypothesis is the major explanation for own-race bias (Hole Byrne, 2010). Additionally, Greeble experiments were carried out. It was found that non-experts had no FFA activation while FFAs of experts fired (Gauthier et, al, 1999). Although these findings do support the expertise hypothesis, some criticisms have been made. For example, studies have not found FFA activation for object stimuli with which the participant was expert (Grill-Spector et al. , 2004) and others have found low and insignificant activation (Moore et al. , 2006). Hence, it is still unknown whether the FFA evolved as specialised neural network dedicated to processing faces. FFA activation to Greebles has come under scrutiny. It has been suggested that the FFA does not fire, because the FFA is specialised for detecting subtle difference in faces and objects as the face hypothesis states. Instead, FFA activates because Greebles are body or animal like (Kanwisher Yovel, 2006) even though they were created to not be animal like. Also, there is a chance that the perceived activation of the FFA is actually an activation of the fusiform body area (Peelen Downing, 2005). Potentially, misrecordings have been taken and fusiform gyrus activation elsewhere on the gyrus has been attributed to the face area (Kanwiser Yovel, 2006). In the future, improved resolution might rectify this. Further to the argument of faces being special, Mc Kone et al. hightlight that the FFA is constant with the location of prosopagnosia lesions (2007). This evidence is strengthened by the finding that some prosopagnosia patients have shown no FFA activation when viewing faces (Kanwisher et al, 1999). Conversely, Steeves’ patient DF showed normal FFA activation despite suffering prosopagnosia (2006). Perhaps evidence from DF suggests that the FFA is important in face but as part as a network. And so there is very strong evidence from neuroimaging to say that faces are special and that there is a specialised neural network. However, supporters of the expertise hypothesis still disagree. In this essay the question of whether faces are special was examined. Psychological studies show that faces are processed in a different way to non-face stimuli. Specifically, faces are processed using configural information whereas objects are processed using featural information. Supporters of the expertise hypothesis argue that this is because of humans’ expertise in making subtle discrimination between faces as a homogeneous class of stimulus. Then the double dissociation between face and object processing in prosopagnosia patients was cited as evidence that humans have developed a specialised neural network for face processing. Again, proponents of the expertise arguments disagree asserting that prosopagnosia is a result of damage to a region of the brain for making subtle discriminations rather than a special face area. Finally, neuroimaging evidence was evaluated and once again, expertise supporters argued against the FFA being a special brain region. As a result of this evidence, I think it can be concluded that nobody knows whether faces are special or if humans have a specialized neural network. 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