The effect of cognitive load on the processing of hierarchical visual information

The visual world is organised hierarchically from global structure to local detail or from the ‘forest’ to the ‘trees’ (Navon, 1977; Palmer, 1975). The present thesis explores the effect of cognitive load on the processing of hierarchical visual information; specifically, we distinguish between the effects of cognitive load on i) whether observers are biased toward prioritising global structure or local detail; ii) the ability to select local and global information, as relevant to tasks or behavioural goals.

The main contributions of this thesis are to show that cognitive load i) affects perceptual bias by making observers less global and more local or, in other words, less likely to see the ‘forest’ for the ‘trees’, and ii) makes it more difficult to selectively attend to the least salient level of hierarchical information. These effects of cognitive load are likely exerted through separate mechanisms. With respect to perceptual bias, we suggest that cognitive load alters relative hemispheric activation and with it the relative priority afforded to global structure and local detail. With respect to selection, we suggest that cognitive load impairs cognitive control and makes it harder to prevent the processing of irrelevant-yet-salient hierarchical information.

Taken together, the findings presented in this thesis suggest that cognitive load exerts significant effects on hierarchical processing, whether through effects on global-local perceptual bias or attentional selection of hierarchical information. As the visual world is structured hierarchically, whether it be the global scene as a whole or individual hierarchical structures such as words or faces, cognitive load – which can vary from person-to-person and within an individual circumstantially – could fundamentally affect how observers ‘see’ the visual world.