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Chloe Callahan-Flintoft, Brad Wyble; Using the N2pc to compare the timing of attentional shifts to categorical and featural targets.. Journal of Vision 2015;15(12):231. doi: 10.1167/15.12.231.
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© ARVO (1962-2015); The Authors (2016-present)
When a target is presented on one side of a visual display, EEG will record a brief negativity from posterior locations on the contralateral scalp about 200ms after target onset. This component, called the N2pc, is thought to reflect the deployment of attention towards the target. The present study contrasted the N2pcs produced by targets defined by feature or by category. Participants viewed two RSVP streams with a 150ms SOA. The distractors were black letters and the targets were either red letters (differing from distractors in feature) or black digits (differing in category). Trials either had one target or two (T1 and T2), with T2 always presented immediately after and on the same side as T1 in all possible combinations of target types. The presentation of the target(s) was followed by another string of distractors and subsequently participants were asked to report what targets they had seen. We found that the N2pc onset was later when T1 was defined by category (digit) versus feature (red letter). From this we predicted that the delay in the localization of attention from a category target would delay the subsequent encoding of that target, such that participants would swap the T1 and T2 in their report more often whenever the first target was specified by category rather than feature. The behavioral data confirmed this prediction. Additionally, in an unexpected finding, the lowest accuracy in reporting both targets involved a categorical T1 (slow localization) followed by a featural T2 (fast localization). This arrangement may have caused the attentional processes evoked by the two attentional sets to collide, thus producing less efficient encoding of the targets from the RSVP stream. The reverse order (feature followed by digit) produced much higher accuracy.
Meeting abstract presented at VSS 2015
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