Figure 416

Recognition memory for faces and pairs of spectacles in a prosopagnosic patient (LH) and normal controls. Data from Farah (1994a).

objects. Such patients have been identified (e.g., Moscovitch, Winocur, & Behrmann, 1997). If face processing involves specific mechanisms, then one might expect that there would be somewhat separate brain regions associated with face and object recognition. Farah and Aguirre (1999) carried out a metaanalysis of relevant PET and fMRI studies, and found that much of the evidence was inconsistent.

However, Kanwisher, McDermott, and Chun (1997) obtained clear findings when they used fMRI to compare brain activity in response to faces, scrambled faces, houses, and hands. They found that there was face-specific activation in parts of the right fusiform gyrus, and these findings have been replicated by others (see Farah & Aguirre, 1999, for details).

Implict knowledge and connectionist models

Most (but not all) prosopagnosics possess some implicit knowledge about the familiarity of faces, face identity, and semantic information that is accessed through faces (e.g., occupation). For example, Bauer and Verfaellie (1988) asked a prosopagnosic patient to select the names correspond ing to presented famous faces. The patient had no explicit knowledge about the faces, because his performance was at chance level. However, there were greater electrodermal responses when the names matched the faces than when they did not, indicating the existence of relevant implicit knowledge.

More evidence that prosopagnosic patients have implicit knowledge about faces was reported by De Haan, Young, and Newcombe (1987). They asked PH to classify names according to whether they belonged to politicians or not, and a famous distractor face was presented along with each name. PH was unable to classify the faces as belonging to politicians or non-politicians. However, his classification times for the names were longer when the distractor face came from a different occupational category to the name. This latter finding points to the existence of implicit knowledge about the famous individuals whose faces were presented.

Some prosopagnosic patients do not seem to possess implicit knowledge about faces. What is different about these patients? According to Kohler and Moscovitch (1997, p. 346), "Prosopagnosic patients who do not show implicit knowledge are those who have a perceptual impairment in analysing incoming information about the physical characteristics of faces."

Burton and Bruce's (1993) interactive activation and competition model (discussed earlier) provides a connectionist account of prosopagnosia and the use of implicit knowledge. Burton et al. (1991) simulated prosopagnosia by reducing the weights on the connections from the face recognition units (FRUs) to the person identity nodes (PINs). This reduced the activation of PINs to faces, and meant that faces were often not identified or recognised as familiar.

Burton et al. (1991) found that their "lesioned" model was able to make use of implicit knowledge in a similar way to prosopagnosic patients. Presentation of a face produced some activation of its PIN and the relevant SlUs, and this facilitated performance on tasks requiring the use of implicit knowledge.

Evaluation

The connectionist model of Burton and Bruce (1993) accounts for many of the basic phenomena associated with prosopagnosia. However, it has problems with some of the findings reported by Young and de Haan (1988). They found that their prosopagnosic patient showed evidence of using implicit knowledge about faces by learning face-name pairings faster when they were correct than when they were incorrect, but did not learn correct face-occupation pairings faster than incorrect ones. According to the model, faces partially activate relevant semantic knowledge, and so both types of correct pairings should have been learned more readily than incorrect pairings.

Farah's two-process model

Farah (1990, 1994a) put forward a two-process model of object recognition of relevance to understanding face recognition. The model distinguishes between the following processes or forms of analysis:

1. Holistic analysis, in which the configuration or overall structure of an object is processed.

2. Analysis by parts, in which processing focuses on the constituent parts of an object.

Farah (1990) argued that holistic analysis and analysis by parts are involved in the recognition of most objects. However, face recognition depends mainly on holistic analysis, and reading words or text mostly involves analytic processing. Evidence supporting the notion that face recognition depends more than object recognition on holistic analysis was reported by Farah (1994a). The participants were presented initially with drawings of faces or houses, and were told to associate a name with each face and each house. Then the participants were presented either with whole faces and houses or with only a single feature (e.g., mouth; front door). Their task was to decide whether a given feature belonged to the individual whose name they had been given previously.

The findings are shown in Figure 4.17. Recognition performance for facial features was much better when the whole face was presented than when only a single feature was presented. In contrast, recognition for house features was very similar in whole and single-feature conditions. These findings suggest that holistic analysis is much more important for face recognition than for object recognition.

Farah (1994a) obtained additional support for her model by studying the face inversion effect. In this effect, the ability to recognise faces is significantly poorer when they are presented in an inverted (upside-down) way than when presented normally. Farah (1994a) found that normal individuals showed the face inversion effect. However, the prosopagnosic patient, LH, showed the opposite effect, having better face recognition for inverted faces (see Figure 4.18). How can we explain these findings? According to Farah (1994a), the face inversion effect occurs because the holistic or configural processing that normal individuals apply to faces presented normally cannot easily be used with inverted faces. However, prosopagnosic patients have very limited ability to use holistic or configural processing, and so their ability to recognise faces does not show the face inversion effect.

The theoretical and empirical approach of Farah (1990, 1994) was developed by Farah et al. (1998). They argued that the notion of holistic processing can be defined in various ways. Their preferred definition was as follows: "it [holistic processing] involves relatively little part decomposition" (Farah et al., 1998, p. 484). What that means is that faces are generally recognised as wholes, and explicit representations of parts of the face (e.g., nose; mouth) play little or no part.

At the empirical level, Farah et al. (1998) pointed out that the previous research discussed by Farah (1990, 1994a) had shown that faces are stored in memory in a holistic form, but had not shown that faces are perceived holistically. They filled this gap in a series of studies. The participants were presented with a face, followed by a mask, followed by a second face. The task was to decide whether the second face was the same as the first. The key manipulation was the nature of the mask, which consisted either of parts of a face arranged randomly or of a whole face. The crucial prediction was as follows: "If faces are recognised as a whole and part representation plays a relatively small role in face recognition, then a mask made up of face parts should be less detrimental than a mask consisting of a whole face."

What did Farah et al. (1998) find? As predicted, face-recognition performance was better when part masks were used than when whole masks were used. This finding suggests that faces were processed holistically. In other conditions, the effects of part and whole masks on word and house recognition were assessed. The beneficial effects of part masks over whole masks were less with house stimuli than with faces, and there

Stop Anxiety Attacks

Stop Anxiety Attacks

Here's How You Could End Anxiety and Panic Attacks For Good Prevent Anxiety in Your Golden Years Without Harmful Prescription Drugs. If You Give Me 15 minutes, I Will Show You a Breakthrough That Will Change The Way You Think About Anxiety and Panic Attacks Forever! If you are still suffering because your doctor can't help you, here's some great news...!

Get My Free Ebook


Post a comment