Running Head: INSIGHTS INTO THE MECHANISMS OF PROCESSING IN 1

FACE SPECIFIC VS. EXPERTISE HYPOTHESES: INSIGHTS INTO THE UNDERLYING MECHANISMS OF FACE PROCESSING IN PROSOPAGNOSIA

BY

SUMAYA LAMB

A thesis Submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Master of Science in Cognitive and Behavioural Neuroscience

Victoria University of Wellington 2018

INSIGHTS INTO THE MECHANISMS OF FACE PROCESSING IN 2 PROSOPAGNOSIA

Abstract A prominent debate in visual centers on the nature of mechanisms underlying face processing. One side of this debate argues that are processed by specialised mechanisms that are not involved in any form of object processing. By contrast, the other side argues that faces are processed by generic mechanisms common to all objects for which we are experts. To distinguish between these two hypotheses, I investigated whether participants with impaired face processing (developmental prosopagnosia) can acquire expertise with novel objects called greebles. To do so, I recruited 10 developmental prosopagnosics and 10 neurotypical control participants. All participants completed a standard training program for developing expertise with greebles, as well as two similar training programs with upright faces and inverted faces. Prosopagnosics were able to acquire expertise with greebles to the same extent as controls but were impaired when learning upright faces. These results demonstrate that deficits for face processing in individuals with prosopagnosia are dissociated from their ability to gain expertise with objects. Overall, the results support the hypothesis that face processing relies on specialised mechanisms, rather than generic expertise mechanisms. Despite their deficits, though, prosopagnosics still showed some evidence of learning with upright faces and showed better learning with upright faces than inverted faces. These findings suggest that prosopagnosics have face-specific mechanisms that are somewhat functional, and that training could be a useful rehabilitation tool in developmental prosopagnosia. Finally, I found substantial heterogeneity among the patterns of performance of the prosopagnosics, suggesting that further investigations into the subtypes of prosopagnosia are warranted.

INSIGHTS INTO THE MECHANISMS OF FACE PROCESSING IN 3 PROSOPAGNOSIA

Acknowledgements To my supervisor, Dr. Tirta Susilo, thank you so much for your endless patience and support these last two years. It’s been an absolute privilege to be your student, and you have gone above and beyond as a supervisor and mentor. Under your guidance I feel as though I have developed dramatically as a researcher in every aspect. I will be forever grateful for the skills, inspiration and opportunities you have given me in what I hope will be a long and successful research career. I’d also like to thank all the members of the Susilo Lab. I have been incredibly lucky to be part of a lab filled with caring, critically minded, and motivated individuals. Special thanks to Angus, Cassandra, Daniel, Hazel, and Lauren. The unwavering support and guidance that you all have given me and continue to give has helped me grow academically and personally. Thank you for always listening, keeping me grounded when my ideas and worries become just a bit too ridiculous, and reminding me that sleeping and taking breaks are things that normal people do. Also, an extra special thank you to Cassandra and Hazel for proof reading this thesis. Thank you to my parents. Thank you for always encouraging me to pursue the things in life that make me happy and thank you for always supporting the many (ever changing) endeavours that followed from that advice. It’s clear that without your support I would not be in the position I am in today. I’d also like to