Ntonia, I. (2016). Modulation of lateralised responses to primary affect. (Unpublished Doctoral thesis, City, University of London)
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Do we use one cerebral hemisphere or both to process positive and negative emotions? Is it more physiologically economical for the brain to initiate responses to both types of primary affect from a unilateral locus, or does our readiness to react to emotional stimuli depend on the differential contribution of each hemisphere based on the approach or avoidance behaviours positive and negative affect elicit? This thesis is concerned with these questions that have so far remained unanswered even though they form a key part of emotional perception research. The behavioural literature has provided evidence for both unilaterally (right hemisphere) and bilaterally derived responses to different types of emotional stimuli, with the directionality of response patterns changing depending on stimulus type and task demands. The neuroimaging literature has addressed whether there is a functional need for the lateralised processing of basic emotional stimuli by mapping subcortical and cortical emotional attention networks, specific to different variants of only negative affect (i.e. fear, sadness). How this subcortically originating lateralisation manifests into observable behaviour however still remains to be established. This research therefore posits that hemispheric lateralisation may be a modulated process, and aims to explore how this modulation guides the directionality of our behavioural responses to primary affect. The thesis introduces a novel methodology that provides the first evidence of the modulation of emotional lateralisation by establishing a behavioural paradigm that can effectively investigate hemispheric lateralisation through measures of response efficiency. The thesis further investigates whether subcortically originating lateralisation may be inferred through its resulting behavioural response, by examining visual field asymmetries in responses to positive and negative affect through nasally and temporally viewed stimuli. Additionally, the thesis considers the modulating properties of contextual emotion-enhancing features of facial expressions such as direct vs. averted gaze and the presence of looming sounds on behavioural responses to negative affect, and also investigates whether individual variability in anxiety levels translates into lateralised responses to affect. Findings from the present thesis suggest that lateralisation is not a sustained, static phenomenon, but in fact a dynamic, modulated process that depends on subtle stimulus-contextual elements to subsequently translate into observable response.
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