Affective bias in visual selective attention

AuszugThe aim of the thesis was to investigate the role of visual selective attention in the processing of distracting emotional material. Specifically, the question was addressed to what extent emotional stimuli are processed independent of attention. From an evolutionary point of view, the rapid identification of emotionally salient information, including danger and reward, and the preparation of fast and appropriate behavioral responses is highly profitable because it enhances the organism’s survivability and reproductive success. Although it is likely that the processing of emotional stimuli is prioritized, the level at which emotion and attention interact and how they do so, remains unclear. To further contribute to the understanding of these mechanisms, three experiments were conducted. All experiments have in common that they required participants to concentrate on an attentional task while disregarding emotional stimuli which were currently presented in the background of the display. In experiment 1, the influence of emotional distracters on an attentional task at hand was examined with particular emphasis on the time-course of this influence. For this reason, attention to the task was measured by using steady-state visual evoked potentials (SSVEPs) which provide a continuous measure of attentional resource allocation. Despite the fact that the emotional stimuli were always task-irrelevant, findings showed that both pleasant and unpleasant background pictures strongly interfered with the attentional task. This effect was reflected in reduced SSVEP amplitudes of the task which covered a rather long time window from approximately 270 ms after picture onset up to one second. The goal in experiment 2 was to examine the influence of this emotional interference on specific cortical and subcortical areas in the brain by using functional magnetic resonance imaging (fMRI). The difficulty of the attentional task was varied to further explore the influence of different levels of task difficulty on the processing of emotional distracters. Findings revealed a significantly reduced BOLD signal in task-related processing areas (i. e., V5/MT+) together with an increase of the signal in emotional processing areas (i. e., the amygdala) in response to the emotional stimuli. These effects were shown under both levels of task difficulty. In the last experiment, the influence of different levels of task difficulty on emotional processing was further investigated with specific emphasis on the time-course of this influence. This experiment used a stimulus presentation which allowed to directly measure the modulatory influences of the attentional task and the emotional distracters by means of separate SSVEPS. In line with the findings of the two previous studies, task-irrelevant emotional pictures were shown to receive prioritized processing independent of the level of task difficulty as indicated by sustained SSVEP amplitude enhancements in response to these pictures. Taken together, the present work strongly suggests that emotional stimuli are processed in a rather automatic way, independent of varying attentional task demands.