Electrophysiological Investigation of Feature-based Attention during Object Perception

We live in a visually rich environment yet our brains are only equipped to process a small fraction of all available information at any point in time. For successful and efficient perception, the brain relies on attention to differentiate and select specific stimuli for further analysis. Attention can be directed to features – feature based attention – which enhances the processing of other similar features independent of spatial location. I have recently shown that the benefits of feature-based attention not only apply to lower-level features, but also to processes of object perception. The aim of the thesis was to examine the behavioural and electrophysiological correlates underlying the influence of feature-based attention on object perception. Chapter 1 measured the electric field activity associated with attending to higher-level features (object contours) and comparing it with the neural activity while attending to motion stimuli. We found temporally later effects for contours relative to motion, suggesting that feature-based attention to objects might be mediated by higher-tier visual areas, such as the lateral occipital cortex. In Chapter 2, I describe a study designed to investigate the time course of neural activity while cueing attention within the feature dimension of shape that more directly targets higher-tier visual areas. Consistent with Chapter 1, I iii found temporally late modulation, but behavioural effects that were weaker than expected. To account for these findings, I proposed a “wrong-turn” model which explains the perceptual benefits and costs coupled to expecting the correct or incorrect feature by taking into consideration the hierarchical structure of the visual system. Moreover, the model also makes specific predictions about the pattern of behavioural and electrophysiological activity while attending to features of varying complexity during object perception. The aim of Chapter 3 was to test the predictions of the model; I cued attention to colour, a lower-level feature essential to perceiving the object. I found much stronger behavioural cueing effects, and a biphasic pattern (early and late) electric brain activity that confirmed the predictions of the model. Together the results indicate that feature-based attention plays an important role in object perception that is mediated by a flexible perceptual system.Ph