Learning to ignore emotional distractors: repetition, affective context and long-term effects

Abstract

It is well known that prolonged experience with certain stimuli modulates their significance in the priority map and leads to a diminished allocation of our attention to them. The present thesis aims to explore the extent to which repetition of the same set of stimuli is effective in supporting a learning process that shapes the attentional filter and allows us to ignore distractors, through the process known as habituation. The primary focus is on understanding how the exposure to repeated task-irrelevant stimuli, particularly emotional ones (both pleasant and unpleasant) might influence the way attention is captured by these images. Additionally, the goal is to determine which stage of emotional processing is affected by this experience, through both behavioral and cortical measures. Finally, we have explored how the habituation mechanisms are influenced by the introduction of a change in the context of experience disrupting its stability, as well as by the lack of exposure to the stimuli themselves for a certain period. To test this, in Experiment 1, the impact of the repetition of distractors was examined by content (i.e., pleasant, unpleasant, and neutral), showing that emotional interference completely habituated with repetition and promptly recovered with novelty. At the cortical level, the enhanced LPP for emotional pictures was attenuated by repetitions, and stimulus novelty only affected emotional, but not neutral distractors in both the RTs and LPP. Alpha-ERD was similarly reduced for repeated emotional and neutral distractors. To better understand how flexible the habituation mechanisms are in novel emotional contexts, in Experiment 2 novel distractors (pleasant or unpleasant or neutral) were introduced among repeated pictures. This prompted a dishabituation response at the behavioral level (i.e., recovery of the response after the habituation) which was more evident in the unpleasant context. Moreover, when novel pictures depicted pleasant contents (i.e., erotica), the dishabituation to unpleasant distractors was attenuated. The LPP and the Alpha-ERD were highly modulated by distractor emotional contents (i.e., trial type), and this modulation persisted across repetitions. Both cortical responses were strongly enhanced when novel pictures were introduced after the habituation phase. Experiment 3 aims to measure the persistence of the habituation over time, that is, the effect of a lack of exposure to the stimulus on habituation. The same set of stimuli were repeated in a habituation phase and, after a day of rest, a test phase. Behavioral interference for emotional stimuli was still reduced by the habituation in the test phase and recovered by the subsequent introduction of new stimuli. The different responses observed at the behavioral and cortical levels correspond to different stages of the elaboration of the stimuli. This suggests that the initial stages of evaluation, where we assess and categorize stimuli, are crucial and supported by the engagement with our motivational systems. This engagement is sustained, and it is reflected in the affective modulation of the Late Positive Potential (LPP). The human brain has the ability to selectively disregard emotionally irrelevant stimuli once the initial evaluation has taken place. This adaptive capability, to overcome the tendency for emotional stimuli to capture our attention, does not occur spontaneously but it is developed through the experience with distracting events. Essentially, it is a learned response originated as a result of the strategy to ignore the distractors and the implicit learning that certain emotional cues hold no significant consequence. In general, this mechanism of inhibition is also sensitive to specific contextual perturbation, like the introduction of novel emotional stimuli and the temporary lack of stimulation, which modulate the response to the already habituated stimuli. In summary, this suggest that cognitive mechanisms enable us to prioritize and filter out emotional distractors after evaluating their significance, emphasizing the importance of implicit learning and context of experience in shaping our response to emotional stimuli.