When viewing the world, the human visual system is exposed to a vast and complex array of sensory information. Typically, the amount of information available exceeds the brain’s capacity for processing at a given point in time. Therefore, the ability to selectively deploy spatial attention, the mechanism that selects certain regions of space for enhanced visual processing at the expense of others, is necessary for seamless functioning. The broad aim of this thesis was to understand the dynamics of one aspect of spatial attention: attention scaling. Attention scaling refers to whether attention resources are focused on a narrow or broad region of the visual field. The first half of the thesis examined whether individual experiences influence attention scaling. Here, we used an inhibition of return (IOR) task to directly measure attention changes across space, which allowed for a valid measurement of spatial attention scaling, uncontaminated by other processes. In Study 1, we measured age differences in attention scale, finding that older adults (60+ years) adopted a narrower distribution of attention compared to younger adults (18-30 years). In Study 2, we then extended this work to explore whether cultural background influences the spatial distribution of attention in the IOR task. Here, we found that on average, those with an East Asian cultural background were more likely to distribute attention broadly compared to those of a Western cultural background. The second half of the thesis then explored the consequences of a narrow versus broad scale of attention for visual perception, and in particular, parvocellular versus magnocellular processing. Firstly, in a review, we critically analysed current theoretical models of attention scaling, concluding that the type of attentional deployment (e.g., exogenous / endogenous), load (both perceptual and cognitive), and unintentional shifts of attention all uniquely influence the relationship between attention scaling and vision. Finally, in Study 3, we directly pitted the zoom lens and selective spatial enhancement models of attention scaling against one another. Recent research suggested that attention scaling solely influenced parvocellular, and not magnocellular processing. However, this research manipulated attention using unfilled shapes, which had the potential to split, rather than scale attention. Therefore, we used a new method to manipulate attention scale, a global motion inducer, which encouraged attention scaling. In line with the zoom lens model, we found that narrowing attention improved both parvocellular, and magnocellular mediated processing. This highlights the importance of carefully operationalising spatial attention to best understand how attention scaling influences visual perception. 

Presenter: Rebecca is a fourth year PhD student in the Research School of Psychology. She completed her Undergraduate Degree in Psychology with Class I Honours and University Medal at the ANU in 2015. Her PhD research explores the relationship between spatial attention and vision, with a particular focus on how both healthy ageing, and cultural background influence these processes. She is supervised by Dr. Stephanie Goodhew, Associate Professor Mark Edwards, Dr. Kim Kiely, and Dr. Eryn Newman.