Electrophysiological correlates of multiple object processing

Several daily activities like walking in a crowded street depend on our ability to process multiple objects simultaneously. According to some theories this ability relies on at least two stages or mechanisms related respectively to visual attention and visual working memory (WM). The early stage of multiple object processing – individuation – is a function of attention that allows the visual system to represent multiple objects simultaneously by selecting a limited number of locations and binding them to basic visual features. A second later stage related to visual working memory encodes in greater detail the indexed objects leading to their full representation. In the present thesis I investigated the functioning of multiple object processing in a set of behavioral and electrophysiological studies focusing on the modulation of two component of the event-related potentials - N2pc and CDA – which have been associated respectively to individuation and visual working memory. In all the experiments of the present thesis I established that both N2pc and CDA were modulated by the number of relevant items during the execution of an enumeration task. I exploited this effect in each Chapter of the present thesis to investigate different aspects of multiple object processing. In particular, in the first and second experiment (Chapter 2) I assessed the existence of a capacity limit in simultaneous processing as predicted by theories of individuation. In Chapter 3 I investigated the role of distracting information in simultaneous individuation. In Chapter 4 I focused on whether high-level features (such as semantic information) are incorporated in the representations produced at the stage of individuation. Finally in Chapter 5 I assessed the role of awareness in multiple object processing using a masking paradigm. The results provided new information on the way early individuation and late WM stages interact for successful object perception, as well as on their functional dissociation during multiple object processing.