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Veronica Mazza, Silvia Pagano, Alfonso Caramazza; Multiple target individuation with and without distracters. Journal of Vision 2012;12(9):1158. doi: 10.1167/12.9.1158.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that the visual system can select simultaneously up to approximately 4 elements in the visual field. However, little evidence exists on how such simultaneous selection takes place when both relevant and irrelevant multiple objects are presented, namely when specific objects have to be distinguished not only from each other but also from other irrelevant ones. Using Event-Related Potential (ERP) recordings this study sought to get new insight into multiple target individuation by combining traditional enumeration paradigms (in which multiple targets are presented in isolation) with typical visual search tasks (in which at least one target is presented among distracters). Participants saw a variable number (from 1 to 4) of lateralized target elements presented with or without distracters in the target side, and performed an enumeration task. Results showed that while an early non-lateralized response (N1, 120-180 ms) is modulated by target numerosity only without distracters in the target side, the amplitudes of a lateralized and later response (N2pc, 180-300 ms) increased as a function of target numerosities in both conditions (reaching a plateau at 3 targets). We propose that the stage reflected in the N1 may correspond to the initial indexing of items on the basis of their spatial properties alone. This stage is sensitive to the overall amount of elements presented in the visual field, rather than to the quantities of a specific subset of (target) elements. In contrast, the N2pc may reflect the component of individuation that binds only relevant properties and locations, as inferred by its lateralized nature and by its target numerosity-related modulations both with and without distracters. As a result of this operation, a coarse representation of the relevant objects becomes available, allowing the visual system to individuate them in the visual field and making them ready for further processing.
Meeting abstract presented at VSS 2012
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