The Role of Physical Image Properties in Facial Expression and Identity Perception

A number of attempts have been made to understand which physical image properties are important for the perception of different facial characteristics. These physical image properties have been broadly split in to two categories; namely facial shape and facial surface. Current accounts of face processing suggest that whilst judgements of facial identity rely approximately equally on facial shape and surface properties, judgements of facial expression are heavily shape dependent. This thesis presents behavioural experiments and fMRI experiments employing multi voxel pattern analysis (MVPA) to investigate the extent to which facial shape and surface properties underpin identity and expression perception and how these image properties are represented neurally. The first empirical chapter presents experiments showing that facial expressions are categorised approximately equally well when either facial shape or surface is the varying image cue. The second empirical chapter shows that neural patterns of response to facial expressions in the Occipital Face Area (OFA) and Superior Temporal Sulcus (STS) are reflected by patterns of perceptual similarity of the different expressions, in turn these patterns of perceptual similarity can be predicted by both facial shape and surface properties. The third empirical chapter demonstrates that distinct patterns of neural response can be found to shape based but not surface based cues to facial identity in the OFA and Fusiform Face Area (FFA). The final experimental chapter in this thesis demonstrates that the newly discovered contrast chimera effect is heavily dependent on the eye region and holistic face representations conveying facial identity. Taken together, these findings show the importance of facial surface as well as facial shape in expression perception. For facial identity both facial shape and surface cues are important for the contrast chimera effect although there are more consistent identity based neural response patterns to facial shape in face responsive brain regions.