Elizabeth (Shuxuan) Li '25

BY ELIZABETH (SHUXUAN) LI '25

Cover Image:: Prosopagnosia, otherwise known as face blindness, is characterized by the inability to distinguish faces. If looking at the image, a prosopagnosic would realize that there are faces on the walls but would have extreme difficulty in telling them apart Image Source: Uppertal, 2014

For humans, the most prominent form of sensory detection has been vision. When interacting with others, humans rely heavily on the visual pathway to obtain information about the content and emotions of the speaker. Under circumstances where communication lacks a visual component, such as phone calls or texting, the brain can easily miss clues about the moods and feelings of those on the other side. Hence, the detection of facial features in others is essential to everyday interaction.

In the past century, psychologists’ attention has been drawn to a small but steady stream of cases where an individual’s facial recognition has been impaired since birth in a condition named “developmental prosopagnosia.” One of the first scientists to study prosopagnosia was German neurologist Joachim Bodamer, who coined the name of the condition as “ProsopAgnosie” in German (Bodamer, 1947). In general terms, developmental prosopagnosia (DP) is “the selective degradation of face perception and face memory” since birth in the absence of previous brain trauma (Duchaine & Nakayama, 2006). Distinct from acquired prosopagnosia, where a major head injury deprives patients of their ability to distinguish faces, developmental prosopagnosics have never been able to recognize faces as successfully as the average individual. In addition to lowered sensitivity to differences in facial features, some developmental prosopagnosics observe one half of someone's face as morphing (hemi-prosopometamorphopsia) or even displace one person’s face as someone else’s (Almeida et al., 2020; Jonas et al, 2018). Systematically, the criteria for a DP diagnosis require (1) impediments in facial recognition abilities to the extent of impacting one’s daily life in significantly negative ways and (2) lab testing using methods such as the CFMT (Psychology Experiments: Cambridge Face Memory Test, n.d.).

This paper first contextualizes developmental prosopagnosia in real life by discussing its consequences on daily functioning; then, it will explore two aspects of face processing that are relevant in understanding the disorder, followed by three notable case studies on DP that each represents different cognitive and neural aspects of the condition.

Notable figures such as English primatologist Jane Goodall (fig. 1) and American actor Brad Pitt have admitted to having prosopagnosia (Sacks, 2010; Staff, 2013). The most common form of prosopagnosia is DP, which occurs in about 2% of the general population (Duchaine & Nakayama, 2006). It has significant impacts on quality of life since the visual info available for prosopagnosics to recognize others is greatly reduced. Given that the inability to recognize faces persists for close family members and even oneself, DP patients may find themselves dumbfounded in a variety of social situations. To identify friends, family, and coworkers, they often report using hair, accessories, and elements of clothing, but these items change day-to-day and are thus unreliable (Dingfelder, 2019). Children with DP suffer at school, leading to reduced social interactions and quality of learning from a young age, which can impede their emotional development and life achievement. In fact, many DPs do not realize that they have the condition at all or doubt if their facial recognition abilities are unreliable enough for a medical diagnosis (Wilson et al., 2010). This can be quite frustrating and further detracts from their everyday experience.

First, faces are processed more holistically (as one) than configurally (in parts), although both are important to processing a face as a whole. One case study on patient Bill Choisser mentioned below demonstrates the dependence of face recognition on holistic processing because despite being prosopagnosic, his configural processing is still intact (Duchaine, 2000). Various electrophysiological and behavioral evidence also demonstrates the importance of holistic processing. EEG data has shown that a sample of DP subjects perceived a face as merely the sum of its parts while normal recognizers exhibited activity that superseded a strictly additive approach (Towler et al., 2018). In addition, DeGutis and colleagues have found that holistic face training helps DPs in recognizing the front view of faces (2014). However, this is not an absolute principle, as psychologists like Susilo et al. (2010) have studied DPs with normal holistic processing. Thus, holistic processing and configural processing both play a part in facial recognition, but the holistic mechanism is more favored.

Second, face processing is “special” in visual recognition in that it occupies certain pathways distinct from the rest of the visual system. In other words, the brain delegates specialized mechanisms to faces but not to other objects. A notable study by Farah et al. (1998) found that individuals performed much worse when recognizing parts of faces than the whole, unscrambled faces. Their performance in identifying parts of non-face stimuli, such as the door to a house, was comparable to recognizing the entire house. The specialization of facial recognition mechanisms is also logical given that they rely more on holistic faces, which require neurons operating at a level larger than simple part recognition. Furthermore, the receptive fields of high-level face cells are much bigger, indicating that the brain tends to perceive a face in its entirety at once (Rolls et al., 2003). In fact, there is a double dissociation between face recognition and object recognition, meaning that these two processes operate from different mechanisms that overlap to a minimal extent, if at all. For example, Bill Choisser had prosopagnosia without object agnosia, an extreme difficulty in recognizing objects. Conversely, there have also been individuals with impaired object recognition and intact face processing, such as patient C.K. (Moscovitch et al., 1997) and Mr. W (Rumiati et al., 1994). Since both disorders can exist without the other, the processes when recognizing a face versus an object are likely distinct.

The causes and presentations of DP have led to several complicated models, partly because the literature on DP is mostly based on case studies rather than general population research. It is

Image 1: Jane Goodall, who is known for her extensive study on chimpanzees, reported that she has had difficulty recognizing and distinguishing faces since childhood (Sacks, 2010). She identifies her close friends by features such as hair and glasses. Image Source: Step, 2010

important to note that, like many other mental disorders, those diagnosed with DP are simply on the extreme end of a range of face-recognizing abilities; the other end of the spectrum is known as “super-recognizers.” Psychologist Tardif and her colleagues at the University of Montreal found that the performance of DPs and superrecognizers can be extrapolated from the data of normal individuals (2019). In other words, DPs are quantitatively rather than qualitatively different from the typical population (Tardif et al., 2019). This is informative in researching and diagnosing DP since it affects how psychologists and neuroscientists categorize and analyze relevant case studies. It also informs their investigation of face processing abilities in the normal population.

DP is a heterogeneous disorder, meaning that there is a myriad of neural etiologies and behavioral symptoms depending on the individual. To provide a better illustration of how this condition plays out, below are three documented case studies on DP.

Bill Choisser (B.C.) was an ambidextrous man who had been around fifty years old when he was tested for DP. He had never been able to recognize faces, and he reported using hair and jeans to identify people. As an MIT graduate, a lawyer, and an engineer, B.C. had an IQ of 131, possessed above-average abilities on low-level tasks such as copying and orientation matching, and had no troubles with spatial navigation. He suffered from minor neurological problems unrelated to DP, and had no visual difficulties other than DP. In numerous face identification tests, he scored below average for most of the tasks. For the one task in which he scored within the normal range, he spent an abnormally long time (>1 min.) assessing the faces and used unusual techniques to tell them apart.

B.C.’s test results present multiple points of interest: first, he did not lack the ability to recognize people’s identities per se, as he scored normally or above average when not using faces as identifiers. Second, B.C. could recognize identical photos of faces but not across novel views. Third, his configural processing was intact while the problem lay somewhere along the facespecific processing system (Duchaine, 2000). Together, these three factors exemplify one of many possible thresholds in the chain of facial processing that may go wrong in DP, as it is a heterogeneous disorder.

Image 2: An inferior view of the brain shows the fusiform face area (FFA) in red. Located within the fusiform gyrus, the FFA responds most preferentially to face stimuli, and prosopagnosics often (but not always) suffer from an impairment or a lesion in this area Image Source: Science, 2015

Another case study concerns C.M., a patient with congenital prosopagnosia who was studied by neurologists Schultz and Bertolucci at the University of Santo Amaro and the Federal University of São Paulo respectively (2011). Congenital prosopagnosia will be subsequently abbreviated as CP, and it is a type of DP. Specifically, while DP does not specify any cause for the dysfunction of face processing from birth, CP is “a deficit in face processing apparent from early childhood in the absence of any underlying neurological basis" (Schultz & Bertolucci, 2011). C.M., who was 46 years old at the time of the study, was bilingual in Portuguese and Greek and worked as an executive. Since childhood, she has relied on voice and other non-face physical characteristics to recognize friends and strangers. Her verbal abilities were significantly above average, while her other non-verbal abilities such as detecting facial emotions were below average. C.M. had a normal memory with no mental pathologies according to SPECT and MRI scans. The case report described her as being able to identify if she was looking at a face versus some other stimuli, but she was not able to ascribe the face to any particular person (Schultz & Bertolucci, 2011). This evidence demonstrates that C.M.’s face perception system was intact, but her facial recognition systems were disrupted.

C.M’s case of congenital prosopagnosia exemplifies that DP patients do not always have degradation in “perception” as suggested earlier by Duchaine and Nakayama; instead,

the malfunction can occur further down the line of face processing in the recognition stage (Duchaine & Nakayama, 2006). Although Schultz and Bertolucci did not report C.M.'s underlying neural activity, they describe that CP individuals in general have significantly smaller anterior fusiform gyrus (Schultz & Bertolucci, 2011), which is located close to the fusiform face area (fig. 2). The anatomical anomalies of congenital prosopagnosics suggest that the fusiform gyrus plays an active role in both the perception and recognition of faces.

The third case is a family study on ten direct and indirect relatives with prosopagnosia and/ or object agnosia (Duchaine et al., 2007). The sample consisted of seven females and three males (plus two additional males believed to have DP but were not tested). Ages ranged from twentythree to sixty-six, and the family members held a variety of occupations, including a geologist, a truck driver, and a physician. No one in the sample had any history of head trauma, and most of them scored within or above the normal range on cognitive tests measuring vocabulary size, auditory memory, nonverbal intelligence, and many other abilities. In contrast, during the facial recognition test, the family members scored statistically significantly below control groups. Whether looking at friends, family, or celebrities, the members in the sample identified very few faces correctly. In addition, the validated CPFT (Cambridge Face Perception Test) measured the family as lacking in facial perception capacities. However, their abilities to recognize emotions from close-up pictures of the eye region are intact. Most but not all family members had normal object recognition (Duchaine et al., 2007).

These presentations suggest that different mechanisms underlie face identity processing and emotion processing, and that prosopagnosia and object agnosia at least partially operate on distinct systems. This case study is also significant because it was one of the first investigations on the inheritance of prosopagnosia, showing that DP has a solid basis in genetics (Duchaine et al., 2007). One investigation on non-syndromic hereditary prosopagnosia suggested that the disorder follows autosomal dominant inheritance (Kennerknecht et al., 2006). Thus, although prosopagnosia does not implicate reduced cognitive ability, its genetic inheritance may reduce the quality of life for relatives.

For most DPs, the most troublesome aspect of the condition is difficulties in social interactions. In lieu of facial recognition, DPs often use hair, articles of clothing, or accessories to recognize close ones. The neurological underpinnings of DP are usually specific to regions and pathways involving face processing, which rely more on a holistic mechanism than configural and use highly specialized pathways of the brain. This specialization of mechanism demonstrates how humans have evolved to pay special attention to face identity and face information.

Since DP presents differently across individuals, case studies are quite useful in parsing out specific causes one factor at a time. For patient B.C., his deficit took place more upstream in the face processing path, although there can be various points where face perception and recognition fail. In a separate case study, patient C.M. demonstrated the importance of the fusiform gyrus and the fusiform face area in face processing. Lastly, the genetic history of a family with prosopagnosia showed an autosomal dominant inheritance pattern in the disorder. This case reveals that DP does not occur in isolation and can often be passed down.

Although limited in scope, case studies are important for identifying potential DPs and predicting the onset of the disorder. However, much of the condition is still being studied, including ways to prevent or improve face blindness. It is possible to better face recognition with training, but improvements are usually modest and cannot be generalized to all prosopagnosics (DeGutis et al., 2014). Psychologists are also searching for non-training treatments such as deep brain stimulation or drug-assisted therapy. Many psychologists and patients with prosopagnosia have helped expand the knowledge of the disorder, and various tests exist for measuring one's acuity with faces. Bill Choisser, one of the aforementioned patients, constructed an extensive archive detailing his experiences with prosopagnosia (Face Blind! Bill’s Face Blindness (Prosopagnosia) Pages - Introduction, n.d.). Furthermore, behavior measurements are readily accessible online on websites such as the Cambridge Face Memory test (Psychology Experiments: Cambridge Face Memory Test, n.d.). Those who believe they have some form of prosopagnosia can contact researchers at faceblind.org (Prosopagnosia Research Center - Faceblind, n.d.). The field of DP welcomes new research from both the patient and research sides. "Since DP presents differently across individuals, case studies are quite useful in parsing out specific causes one factor at a time."

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