Neurophysiological mechanisms of attentional capture and suppression by emotionally salient pictures: investigations with EEG and MEG
The timing and brain function of attentional capture of emotional distractive stimuli is still unclear. The purpose of current thesis is to examine the effects of physical stimulus properties, emotional salience and voluntary control on attentional capture and brain function. Three sets of experiments were carried out to: (1) examine the effect of emotional salience and spatial frequency on attention capture and event-related potentials (ERPs) in a visual search task; (2) replicate the behavioural and ERP results of an emotion-induced blindness paradigm (Hoffman et al, 2020) that addresses some prominent drawbacks of previous emotional capture paradigms; (3) identify the neuroanatomical sources of MEG responses measured concurrently with the ERP data of Experiment 2. The results of Experiment 1 showed that both high and low anxious people pay more attention to threatening faces compared to neutral pictures. In contrast, only individuals with high anxiety showed a pronounced P1 component (an early visual ERP component) to low-spatial-frequency information. Experiment 2 confirmed that negative pictures capture attention when they are task related, but that attentional capture of emotional pictures was affected by the attention allocated to the pictures. The ERP results point to two important stages of processing: an earlier stage, indexed by an early posterior negativity (EPN) component, in which attention is automatically captured by emotional stimuli; and a subsequent stage, indexed by a P3b component, in which attentional processing can be voluntarily suppressed. The MEG source analyses of Experiment 3 identified neuroanatomical generators active during these two stages. The EPN time window was dominated by a robust activation of the anterior cingulate cortex during processing of negative pictures, but not neutral pictures. The subsequent P3b epoch was associated with two functionally, temporally and anatomically distinct clusters of activation, first of the insula and, then of anterior cingulate cortex. The anatomical locations, properties and timing of these brain responses are best explained by a “salience network” consisting of the anterior insula and anterior cingulate cortex (Menon and Uddin, 2010; Uddin, 2015), which operate to detect and process emotionally salient stimuli and maintain a task set.