The effect of normal aging on the social perception of faces

Typical aging is associated with declined cognitive functions and neural deterioration. This thesis investigates the effect of normal aging on social perception of facial emotion and facial identity. Firstly, this thesis examines older adults’ ability to perceive facial emotions and facial identities with subtle changes using behavioural investigations. It is revealed that normal aging is linked with declined ability to make fine-grained judgements in the perception of facial emotion (anger and happiness) and facial identity (upright- and inverted-), but not for facial traits judgement. In addition, the relationship between age and each face perceptual performance were explored using regression model fitting. Additionally, this thesis further examines whether typical aging is associated with the perception of subtle changes in facial emotion and facial identity with older adult faces, and whether the age- related facial identity perceptual decline is a face-specific decline or it extends to non-social perception. I developed novel tasks that permitted the ability to assess facial emotion (happiness perception), facial identity, and non-social perception (object perception) across similar task parameters. It is observed that older adults have decreased ability to make fine- grained judgements in the perception of happiness and facial identity (from older adult faces), but not for non-social object perception. These behavioural findings are discussed with theories within the current literature. This thesis also explored the neural mechanisms underlying social perception in older adults using non-invasive high-frequency transcranial random-noise stimulation (tRNS) and electroencephalogram (EEG). The results revealed that stimulating inferior frontal cortex facilitates older adults’ anger perception, especially low- performing older adults. The event-related potentials (ERPs) results have shown that older participants exhibited neural overactivation in the left frontal and centromedial region (100- 200ms stimuli onset) and frontal region (250-850ms stimuli onset) during emotion perception. These findings are discussed in the context of existing literature on normal aging and social perception.