Examining the effect of perceptual load on selective attention in the context of emotional facial expressions using fMRI

In this dissertation, the roles of perceptual load and dilution explanations in the selective attention were examined. In this context, three separate experiments (visual search task) related to each other were conducted. Letters were used in Experiment-1, facial expressions were used in Experiment-2 and 3. The study focuses on task-relevant and task-irrelevant load separation, which is the fundamental distinction between perceptual load and dilution. In this context, cue set size determines the perceptual load, and display set size determines the dilution—the central distractors presented as neutral, congruent, and incongruent. In Experiment-1, the roles of perceptual load and dilution in the selective attention and the confounding effect of the display duration were examined with 51 volunteer participants (26 female, 25 male). As a result, while the perceptual load theory is not supported, the zoom-limited dilution explanation has been kept only in the long-term duration. Thus, the confounding effect of the display duration has been revealed. In Experiment-2, perceptual load and dilution were examined in the context of the stimuli' emotional valance with 60 volunteer participants (30 female, 30 male). For this reason, positive (happy) and negative (angry) emotional facial expressions were used. As a result, neither the perceptual load theory nor the dilution explanation was supported. Besides, the negative stimuli affected performance only if the task was difficult. In Experiment-3, the neural basis of perceptual load and dilution on the basis of emotional stimuli were examined using fMRI with 30 volunteer participants (30 female). As a result, there was no distractor interference effect under any conditions. Although FEF, DLPFC, and ACC activations increase with high load and dilution. The emotional expressions did not lead to AMG activation. In summary, it was revealed that the confounding effect of the display duration should be taken into account in the perceptual load and dilution and the importance of how the congruency effect is defined. Also, it is thought that controlling arousal and saliency levels of the stimuli may be the reason why not observing the main effect of the emotional expressions.