The process of object recognition seems to be fed by multiple systems. Study of brain damaged patients reveals a marked distinction between the processes of object classification and recognizing individual objects amongst of general class of generic objects (Logothetis & Sheinberg, 1996). One visual recognition network may represent objects by compositing different views, while another may depict objects through the spatial arrangement of geons (Logothetis & Sheinberg, 1996).
Face perception involves major activation of bilateral extrastriate areas, such as the fusiform face area and occipital face area (Kanwisher, McDermot, & Chun, 1997). Other areas that experience marked activation include the superior temporal sulcus, the amygdala, and the anterior/inferior cortex of the temporal lobe. The fusiform face area is crucial to identifying and remembering faces. Lesions in this area cause prosopagnosia (Damasio, Tranel, & Damasio, 1990).
The problem of how face perception differs from object recognition is interesting because of the implications of this information for developing interventions to ameliorate the suffering of those who suffer from dysfunction in these areas. Also, this information lies at the core of a system and network of assertions that form the substrate of knowledge and inform the enduring search for truth that is science. Face-perception is often used as an example of domain-specificity in the brain, however, there is mounting evidence to the contrary (Gerlach, Klargaard, & Starrfelt, 2016).
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There is an increase of activity in the face-selective fusiform cortex in response to fearful expressions, indicating feedback from the amygdala. This connection implicates the involvement of several other brain areas, which will be discussed in the body paragraphs (Vuilleumier & Pourtois, 2007). The degree of impairment in face perception positively correlates with the degree of impairment in object processing (Gerlach, Klargaard, & Starrfelt, 2016). Lesions in the brain can impede certain aspects of face perception, while leaving others intact. For instance, facial emotion, age, and gender (Tranel, Damasio, & Damasio, 1988).
Variety of theories and claims… The way in which data is processed by the visual cortex has been classically represented as a hierarchy of increasing sophistication of representation (Riesenhuber & Poggio, 1999). Visual processing appears to be organized in a bottom-up hierarchy of ventral areas(list areas). However, increasingly processes of a top-down nature are thought to be instrumental in visual perception (Bar et al., 2006). One model proposed that low spatial frequencies initiate top-down processes projected from orbitofrontal to visual cortex (Bar et al., 2006). The degree to which these models map onto higher order visual processing, including object and face perception, is still underexplored (Riesenhuber & Poggio, 1999).
Variety of perspectives on face perception… Face perception is thought to occur as a result of specialization in discreet brain regions (McCarthy, Puce, Gore, & Allison, 1997) Bilateral regions of posterior fusiform gyrus activated by viewing faces among non-objects (McCarthy, Puce, Gore, & Allison, 1997). When faces are viewed amongst objects, activity is increased only in a focal right fusiform region (McCarthy, Puce, Gore, & Allison, 1997). The facial fusiform gyrus can be shown to respond specifically to faces, as opposed to modulating visual attention, object classification, or processing of non-facial forms. (Kanwisher, McDermtt, & Chun, 1997). Patient with right hemispherectomy, but no damage to the left hemisphere, demonstrates that prosopagnosia can occur without left hemisphere damage (Sergent & Villemure, 1989). When faces are viewed amongst objects, activity is increased only in a focal right fusiform region (McCarthy, Puce, Gore, & Allison, 1997).
Perception of faces requires multiple stages of processing. The Occipital Face Area represents first stage in the bottom-up, hierarchical face perception network (Pitcher, Walsh, & Duchaine, 2001). OFA preferentially analyzes individual facial features (Pitcher, Walsh, & Duchaine, 2001). Emotional reading of faces stimulates activity in the amygdala. Increased activity in fusiform cortex disappears with damage to the amygdala (Vuilleumier & Pourtois, 2007).
Bottom up vs top down… Face perception is informed by affective readings of faces, in particular, expressions depicting fear (Vuilleumier & Pourtois, 2007). In a case of acquired prosopagnosia with intact right middle fusiform gyrus, patient was still able to select faces displaying fearful expressions quicker than neutral faces (Peelen, Lucas, Mayer, & Vuilleumier, 2009).
Studies of prosopagnosia… Object recognition impaired when lesions occur in specific areas of the brain; right lateral fusiform gyrus, ventrolateral occipito-temporal cortex. Prosopagnosia sufferer may become impaired in one, or all, aspects of face perception (Tranel, Damasio, & Damasio, 1988). Prosopagnosia caused by bilateral cerebral lesions involving visual system (Tranel & Damasio, 1985). Under experimental conditions, patients have responded to faces of friends and family with significant electrodermal skin conductance responses, indicating that an early step in visual recognition is still occurring, even outside of their awareness (Tranel & Damasio, 1985).
Prosopagnosia is often considered to be exclusively associated with damage to right hemisphere (De Renzi, Perani, Carlesimo, Silveri, & Fazio, 1994). Impairment of topographical memory often co-occurs with developmental prosopagnosia (Klargaard, Starrfelt, Petersen, & Gerlach, 2016.) The evidence of RH exclusivity in relation to prosopagnosia is somewhat ambiguous, as real-world instances of hemispheric damage are bilateral (De Renzi, Perani, Carlesimo, Silveri, & Fazio, 1994). The first reported prosopagnosia in a right hemispherectomized person revealed that the subject was unable to recognize or remember the faces of family and acquaintances (Sergent & Villemure, 1989).
Patient identified familiar people through visual context clues and could recall semantic information regarding them. Patient was unaware of their deficit in face perception, and of the concept of identifying others through face perception in general. This indicates that other right hemispherectomized patients may also have undiagnosed prosopagnosia (Sergent & Villemure, 1989).
Summary of perspectives and evidence. Overview of face perception and its differences from object perception. Commentary on prosopagnosia case studies. My own observations and opinions on how face perception differs from object perception. How do disorders regarding face perception impact individuals? Implications for interpersonal communication. If individuals are unable to reliably identify people, they may not be able to carry on the business of daily life without aid.
It seems that part of prosopagnosia is the lack of awareness of the condition itself by the sufferer. This could lead to stressful or dangerous consequences for the suffering individual, both socially and logistically. Policy implications… The needs of prosopagnosia sufferers ought to be anticipated and provided. Patients who receive hemispherectomies should be closely monitored and tested for prosopagnosia.
