OHBA SEMINAR SERIES
Dr Thomas Töllner (LMU Munich)
Monday, 14 December 2015, 2pm to 3pm
Department of Psychiatry Seminar Room
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The Posterior Contralateral Negativity (PCN/N2pc) as a neuro-chronometric measure of attentional selection at the saliency map
Over the last two decades, the Posterior Contralateral Negativity (PCN; or N2pc) has been a powerful measure for studying various theories of visual selective attention. While there is a consensus that this component is linked to the selection of task-relevant objects amongst distractor items in visual space, the exact (interplay of) mechanisms that give rise to this potential remain controversial. I will present a series of visual search studies designed to explore the idea that the PCN reflects the target’s saliency signal at the attention-guiding master map, as envisaged by salience summation models. Accordingly, dimensionally organized analyzer units (e.g., color, shape) encode the presence of feature contrast for all locations in parallel, with feature contrast computations being modulated by top-down expectancy and intertrial history biases. These signals are then integrated by an overall-saliency map representation, which guides the deployment of focal attention to the most active map location. Crucially, such saliency map activations suffice to indicate the presence and location, but not the identity, of the target. I will outline evidence that the PCN exhibits properties exactly as predicted from this framework: we found PCN activations being gradually speeded and amplified the more relative to less the target differed from its surround, as well as when the target identity was predictable within, or kept constant across, trials. Overall, this set of findings support the view that the PCN indexes the times required for pre-attentive saliency computations to determine the target for focal-attentional selection.