A critical exploration of the factors influencing the relationship between spatial attention scale and visual perception

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 deploy spatial attention, the mechanism that selects specific regions of space for enhanced visual processing at the expense of others, is necessary for seamless functioning. The overall goal of this thesis was to understand the causes and consequences 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. An inhibition of return (IOR) task was used to achieve this. Compared to previous work exploring individual differences in attention scale, the IOR task directly measures changes in attention across space, allowing for a valid measurement of attention scale uncontaminated by other processes. Using the IOR task, Chapter 4 tested the effect of age on attention scale. Two experiments found that older adults (60+ years) adopted a narrower attention scale in comparison to younger adults (18-30 years). Chapter 5 then extended this work by exploring whether cultural background influences the spatial distribution of attention. In contrast to past research, this study found no cultural difference in attention distribution. Instead a reliable difference in response speed was found, where Western participants were relatively faster to respond to targets in the IOR task compared to East Asian participants. This suggests that factors other than attention drive cultural differences in cognition and response speed. The second half of the thesis explored the effect of a narrow versus broad scale of attention for visual perception, and in particular, parvocellular versus magnocellular processing. In Chapter 6, a critical analysis of current theoretical models of attention scaling was conducted, which concluded that the specific methodology employed to manipulate attention scale uniquely influences the relationship between attention scaling and vision. Finally, in Chapter 7, the zoom lens and selective spatial enhancement models of attention scaling were directly pitted against one another. While the zoom lens model proposes that narrowing attention improves all aspects of vision, the selective spatial enhancement model purports that narrowing attention influences parvocellular, and not magnocellular processing. However, recent research favouring the selective spatial enhancement model used unfilled shapes to manipulate attention, which had the potential to shape attention as an annulus, rather than scale attention. Therefore, in Chapter 7, two new methods were used to manipulate attention, which encouraged scaling. These were a global motion inducer and a Glass inducer. Consistent with the zoom lens model, it was found that narrowing attention improved both parvocellular, and magnocellular mediated processing. Taken together, this highlights the importance of carefully operationalising spatial attention to understand best how scaling attention influences visual perception