Attention to emotional stimuli in motion: Electrophysiological and behavior correlates

Abstract

Attention has evolved as a cognitive tool that facilitates the detection of relevant events. This process is traditionally classified into two types: exogenous or bottom-up attention, driven automatically by external stimulus properties as salience or novelty of stimuli, and endogenous or top-down attention, characterized by the voluntary selection of the stimuli based on internal individual factors as current goals or knowledge. Two of the most conspicuous characteristics that make a stimulus relevant are its emotional content and its dynamic condition (especially looming), which are prioritized during both exogenous and endogenous attention. However, these characteristics have been explored separately, their combined effect on both types of attention remaining unexplored. The present Thesis examined this issue through behavioral and electrophysiological (event-related potentials or ERPs) indices. In addition, to increase the realism of looming and provide greater ecological validity to the experiments in this Thesis, all stimuli were presented through a 3D, high-quality stereoscopic stimulation system. The main purposes were to explore the interaction effect of looming motion and emotional content of stimulation through ERPs and behavioral indices i) on exogenous attention (Experiment 1), ii) on endogenous attention (Experiment 2), and iii) to analyze common (and divergent) characteristics of both types of attention in response to these stimuli (Study 3). This latter study was possible since the same participants (n=71) took part in both experiments, following a within-subject design in counterbalanced order with six months between them to minimize habituation and/or fatigue. In Experiment 1 (exogenous attention), emotional and neutral stimuli (animals) presenting or not looming motion acted as distractors while participants attended to the orientation (coincident or not) of two lines. In Experiment 2, participants had to direct their endogenous attention to animals (which were identical to those of Experiment 1) by indicating whether the animals were vertebrates or invertebrates. Behavioral results in these studies were characterized by faster and more accurate responses to threatening stimuli (negativity bias), with a specific advantage for looming threatening stimuli in the case of endogenous attention (Experiment 2). Neural results on attentional capture (Experiment 1) reflected looming positive distractors as preferential capturers in relatively far distances (whose processing was reflected in early and mid-latency ERP components, P1p and N2po), whereas negative distractors (looming and static) captured attention in the peripersonal space (whose processing was reflected later, in LPP), at close distances (with a potential contribution of endogenous attention at this stage). On the other hand, endogenous attention results (Experiment 2) revealed that both positive and negative looming conditions recruited greater attentional resources as reflected in mid (P2p) and late processing stages (LPP). The comparative study (Study 3) supported the bias of the attentional system towards looming emotional stimuli and showed a two-phase processing of looming emotional stimulation. The early processing stage is characterized by a looming positivity offset where looming positive stimulation recruits attention to a greater extent when stimuli are relatively far and, therefore, perceived as less threatening, allowing the exploration and interaction with the environment. In the second stage, attentional processes are redirected towards threatening content that, at this moment, are within the peripersonal space (a highly activating context), triggering faster and more accurate responses towards this type of stimulation. Therefore, these results are mediated by an interaction of stimulus distance, emotional valence, and motion.