Crossmodal Load and Selective Attention

This thesis explores a current dominant theory of attention - the load theory of selective attention and cognitive control (Lavie et al., 2004). Load theory has been posited as a potential resolution to the long-running debate over the locus of selection in attention. Numerous studies confirm that high visual perceptual load in a relevant task leads to reduced interference from task-relevant distractors; whereas high working memory load leads to increased interference from task-irrelevant distractors in a relevant task. However, very few studies have directly tested perceptual and working memory load effects on the processing of task-relevant stimuli, and even fewer studies have tested the impact of load on processing both within and between different sensory modalities.

This thesis details several novel experiments that test both visual and auditory perceptual and working memory load effects on task-relevant change detection in a change-blindness “flicker” task. Results indicate that both high visual and auditory perceptual load can impact on change detection, which implies that the perceptual load model can account for load effects on change detection, both within and between different sensory modalities. Results also indicate that high visual working memory load can impact on change detection. By contrast, high auditory working memory load did not appear to impact change detection. These findings do not directly challenge load theory per-se, but instead highlight how working memory load can have markedly different effects in different experimental paradigms.

The final part of this thesis explores whether high perceptual load can attenuate distraction from highly emotionally salient stimuli. The findings suggest that potent emotional stimuli can “breakthrough” and override the effects of high perceptual load - a result that presents a challenge to load theory.

All findings are discussed with reference to new challenges to load theory, particularly the “dilution” argument.