The electrophysiological correlates of processing expression intensities along emotion trajectories

In this thesis we utilise the Event Related Potential (ERP) technique to examine how expression intensities are processed along happy and angry emotion trajectories (defined as the continua of expression intensities between Neutral and Prototypical expressions). Emotion trajectories were formed by morphing the emotional faces to display expressions that were 20%, 40%, 60%, 80%, or 100% of the full expression. In both Experiments 1 and 2, we recorded Electroencephalography (EEG) while participants viewed faces that were either neutral in expression, or portrayed happy or angry expressions along an emotion trajectory. In Experiment 1, we examined the automaticity of expression intensity processing where participants were simply required to view the stimuli while performing an infrequent, unrelated task. In Experiment 2, we examined whether voluntary attention to emotion modulates expression intensity processing. In Experiment 1, we found that only high intensities of expression intensities were processed automatically, as shown by modulation of the Early Posterior Negativity (EPN). In Experiment 2, we found facilitatory effects of voluntary attention on expression intensity processing, reflected by graded modulation of the N170 based on expression intensity. Additionally, EPN amplitudes were more graded for angry expressions than happy expression intensities, suggesting that angry intensities were processed in more depth than happy ones. EPN amplitudes for each expression intensity were negatively correlated with the proportions of expressions rated 'emotional', suggesting that the EPN is involved in the perception of the emotion rather than the physical differences between expression intensities. In Experiment 3, we examined whether EPN modulation would reflect perceptual shifts in emotion intensity observed in behavioural adaptation/aftereffects experiments. We replicated EPN intensity effects for adaptor stimuli, but not the test stimuli. Furthermore, there were no systematic behavioural effects to assess whether the EPN might reflect perceptual shifts. Further refinement of the adaptation/aftereffects paradigm to utilise in EEG can help tease apart physical and perceptual shifts of emotion. Overall, this thesis provides evidence that expression intensity is coded in the brain, and that it is modulated by explicit attention to emotion. Furthermore, the data suggest that the EPN is associated with participants' evaluation of emotion rather than physical stimulus processing.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Psychology

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2019

Author dc:creator

• Vogeti, Sreekari

Advisor dc:contributor.advisor

• Corballis, PM

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/49247

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/49247