Network dynamics of human face perception: the salience of infant faces and implications for caregiving
Keywords: caregiving
cuteness
face processing

This thesis provides novel neuroimaging insights into the brain activity related to the processing of highly salient infant faces. Specifically, I provide new information about the spatial and temporal aspects of brain activity for processing infant faces within four experimental investigations. Overall, the presented findings provide novel, important insights into: (1) our current understanding of how the brain processes salient, infant faces, (2) human face perception more generally, and (3) potential implications for how we provide care to our young.
In Chapter 1, I review the literature on human face processing, and infant face processing. I draw together insights from prosopagnosia and single-cell studies in primates, moving on to discuss functional neuroimaging findings highlighting a dedicated spatial network of regions for face processing within the brain. The current evidence has good knowledge of ‘what’ and ‘where,’ but lacks a temporal dimension: ‘when.’ I then move on to discuss models of face perception, and how the dominant narrative involves a hierarchical, feedforward process, which is at odds with current knowledge about top-down interactions between brain regions. Lastly, I summarise our current understanding of human parental brain networks.
In Chapter 2, I present two quantitative meta-analyses of aggregated fMRI data, using activation likelihood estimation (ALE) analysis. First, I explore nulliparous women viewing infant faces, and second, I explore mothers viewing their own infants’ face. I present findings relating to the spatial coordinates of these two intriguing contrasts, including the apparent left lateralisation of infant face processing in motherhood. I reflect upon how the field of fMRI studies has thus far been limited in its ability to explain the temporal dimension of face processing (“when”) and set a precedent for a greater exploration of infant face processing using temporally sensitive brain imaging methodology and analytic methods.
In Chapter 3, I present the analysis of a dataset exploring how the human brain processes infant and adult faces, replicating previous findings of a privileged processing route when viewing infant faces to support sensitive and swift caregiving. I then advance the field by exploring how the human brain also processes juvenile and adult animal faces to test the hypothesis that the infant schema may operate in a cross-species fashion. I report evidence demonstrating that baby animals (kittens and puppies) also trigger an early orbitofrontal cortex response (120ms), that guides the brain to provide sensitive caregiving – “cuteness ignition”.
In Chapter 4, I analyse the same dataset as in Chapter 3, this time using a classifier (discriminant analysis) to pose the question as to how the adult brain categorises different kinds of faces. This chapter provides proof of principle for the ability of classification analysis to discover the spatiotemporal features needed to separate and predict up to six classes of face stimuli. The importance of the beta band and the time window of 60-180ms post stimulus presentation for face categorisation are both emphasised. The results provide further evidence for the importance of “when” components in brain activity within the human brain, especially when it comes to distinguishing between highly salient categories such as “cute” baby and baby animal faces. This method also provides exciting new avenues for research into the human parental brain and temporally sensitive parent-infant interactions.
Chapter 5 addresses how we can use more nuanced experimental paradigms in fMRI, combined with sensitive network analysis, to draw inferences about how the brain learns about characterological features of infant faces (emotionality). While previous chapters explored the short ‘when’ of infant face processing, this chapter addresses the long ‘when’ involving learning. I report upon a network involving orbitofrontal cortex, amygdala and hippocampus, which is more active for infant faces with a happier temperament and expression of emotionality. This has important implications for social learning, and perhaps for attachment and empathy.
Lastly, in Chapter 6 I conclude by drawing together all findings from the thesis to demonstrate how a comprehensive understanding of cognitive processes within the brain necessitates ‘what,’ ‘where,’ and crucially, ‘when’ information. I discuss how this thesis provides evidence of parallel processing pathways, and the likely presence of top-down predictions arising from this structure. I discuss the crucial role of the orbitofrontal cortex in salient face processing, and advance a new theoretical model for salient face processing that unites ‘cuteness ignition’ with current theoretical top-down models of object processing.