A neuropsychological approach to dissect face perception and perceptual expertise

The human face plays a critical role in successful social interactions. By adulthood, we are very adept at extracting identity, sex, race, emotions, and social signals from faces. Impairments to this fundamental ability may reduce our quality of life and well being. Our proficiency with faces seems to rely on holistic processing which integrates facial parts into a unified spatial configuration or perceptual whole. This holistic processing is generally not seen for other objects. Given the importance of the human face, we propose to investigate the brain mechanisms underlying our expert ability to process faces and the adaptability of these mechanisms to our experiences.

This research goal is strongly motivated by two opposing hypotheses. Importantly, these two hypotheses address the plasticity of the adult human brain. According to the face-specificity hypothesis, the proficiency for face recognition is due to a specialised network of brain regions developed by adulthood that processes only faces. Alternatively, people have extensive experience interacting with each other since birth. According to the expertise hypothesis, the putative face network might remain flexible even in adulthood so that it may be recruited to recognise other objects if one has extensive experience with examples of those objects. For example, dog judges have extensive experience with different breeds of dogs and show holistic processing of dogs.

To test these two competing hypotheses, we focus on individuals who have profoundly lost their ability to recognise faces through brain injury. These individual cannot visually recognise family members, close friends, or even themselves. In rare cases, the ability to recognise non-face objects is fully preserved. These individuals with acquired pure prosopagnosia can still identify people from the voice or other non-visual information, and their face recognition impairment cannot be explained by loss of visual acuity, memory and intelligence. These cases provide a unique and timely opportunity to test whether patients can acquire perceptual expertise with non-face objects, thereby directly testing the face-specificity and expertise hypotheses. We have access to several cases of acquired pure prosopagnosia, and will attempt to train them to become perceptual experts with novel objects and measure their recognition performance during the course of training on a series of perceptual tests that tap holistic processes. In contrast to previous work, we will use an intensive training program (at least 20 hours); we will emulate natural learning situations (e.g., learning the objects from different viewpoints and under different lighting conditions); and we will track the time course of expertise acquisition for patients.

The patients' performance with the novel objects will be compared to age-, sex- and education-matched neurologically intact volunteers and to a larger sample of younger volunteers. For the younger control volunteers, we further test a novel prediction of the expertise hypothesis: That objects of expertise will compete with faces for limited neural resources available. To test this prediction, we will use functional brain imaging to measure how responses from brain regions of the putative face network are affected as volunteers becomes experts with our novel objects. The results will complement those from the patients.

In sum, we combine a neuropsychological approach with intensive training and brain imaging to dissect the mechanisms of proficient face recognition. The results will have an impact on clinical populations which can result in face recognition deficits, such as Alzheimer's disease, stroke patients, and developmental disorders that affect social interactions (e.g., Autism). Although we focus on individual case studies, our approach will lead to definitive results which will have a broad impact on the neurologically-intact population and these clinical populations.

Our proposed research has an impact for psychologists, neuropsychologists, social scientists, clinicians and therapists, and will have broad appeal to the public. Here we summarise the social and health impact of the proposed research.

Social and Public Impact
First and foremost, our proposed research will directly benefit the individuals with acquired pure prosopagnosia who volunteer their time and energy to participate in our study. They are acutely aware of their deficit and must cope with it on a daily basis. The findings will help them understand the deficit while at the same time allowing them to contribute to science. Our quantitative test batteries may also help to identify areas of strengths and weaknesses in their perceptual abilities. We can therefore target their weaknesses or capitalise on their strengths to individually help them cope with their face recognition deficits. Furthermore, our research will have a positive impact on family, friends and the general public, as they will also have a better understanding and awareness of perceptual face recognition deficit. For instance, our results will highlight that poor social interactions can be due to perceptual deficits rather than due to deficits in social and communication skills.

Second, our proposed research will have an impact on more common and potentially more devastating clinical conditions. Although cases of acquired prosopagnosia are relatively rare, the outcomes of our proposed research will help in other clinical domains. For example, strokes or dementia can lead to profound visual deficits in both face and object recognition. There is also growing evidence for a form of congenital or developmental prosopagnosia, which is a life-long impairment in face recognition that is not caused by brain damage. These cases of congenital prosopagnosia would be highly prevalent in the population (about 2%). Even though the two forms of prosopagnosia are likely to be qualitatively different, the outcomes of this proposed research can help develop better assessment tools and rehabilitation programs for these people. Lastly, there are also developmental disorders, such as Autism, that can lead to abnormal face recognition and social interaction skills.

Health Impact
Finally, our proposed research will have an impact on clinicians and therapists. Through them, our research outcomes can have an impact on national health in the long term. Our scientific objectives are to understand proficient face recognition at the theoretical, behavioural and neural level. The outcome of the proposed research may also show brain plasticity even for the damaged adult brain. Thus, this holistic understanding of proficient face recognition will allow clinicians and therapists to develop more effective therapies targeted for individual patients. Furthermore, our proposed research can help them develop better rehabilitative programs and better neuropsychological assessment tools.

Overall, by testing rare cases of acquired pure prosopagnosia, this collaborative grant is an excellent opportunity to put the UK in the forefront of a highly prominent and socially important topic in psychology, neuropsychology, and social/cognitive neuroscience.