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. 2008 Mar;45(2):240-9.
doi: 10.1111/j.1469-8986.2007.00611.x. Epub 2007 Oct 26.

The N2pc component and its links to attention shifts and spatially selective visual processing

Monika Kiss  1 , José Van Velzen, Martin Eimer
Affiliations

The N2pc component and its links to attention shifts and spatially selective visual processing

Monika Kiss et al. Psychophysiology. 2008 Mar.

Abstract

The N2pc component has recently become a popular tool in attention research. To investigate whether this component exclusively reflects attentional target selection or also prior stages in attentional processing (covert orienting, target-unspecific spatial attention), a spatial cuing procedure was combined with a visual search task. In some blocks, informative cues indicated the side of upcoming singleton targets that were present on most trials among uniform distractors. In other blocks, cues were spatially uninformative, and no preparatory shifts of attention were possible. The N2pc in response to targets was unaffected by this manipulation, showing that this component is not associated with attention shifts. Following informative cues, an attenuated N2pc was elicited by uniform nontarget arrays, suggesting that the N2pc may also reflect spatially specific processing of stimulus features at task-relevant locations prior to target selection.

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Figures

Figure 1
Figure 1
Illustration of the stimulus sequence presented on individual trials. A symmetric cue array consisting of one red and one blue triangle was followed after an empty interval of 700 ms by a circular search array. Search arrays contained a diamond target among distractors (squares) on two thirds of all trials.
Figure 2
Figure 2
Left and middle panels: Grand-averaged ERPs elicited in the cue-target interval in response to spatially informative cues (left) and uninformative cues (middle) over the left and right hemisphere at frontocentral (FC5/6, top) and lateral posterior (PO7/8, bottom) electrode pairs. Waveforms show the 800 ms interval following the onset of a colour cue that signalled a leftward (solid lines) or rightward (dashed lines) attention shift. For the uninformative cue condition, where cues were spatially non-predictive, waveforms were computed on the basis of the mapping of cue colour to direction of attention that was relevant in the informative cue condition. Please note the different voltage scales for frontocentral and posterior electrodes. Right panel: Difference waveforms obtained at FC5/6 (top), and PO7/8 (bottom) in the cue-target interval in response to spatially informative cues (solid lines) and uninformative cues (dashed lines). Enhanced negativities contralateral to the cued side are reflected by positive values (downward deflections), and enhanced contralateral positivities are reflected by negative values (upward deflections). ADAN: Anterior Directing Attention Negativity; LDAP: Late Directing Attention Positivity.
Figure 3
Figure 3
Grand-averaged visual ERPs elicited in the 1000 ms interval after the onset of a visual search array at lateral posterior electrodes PO7/8. Top: ERPs in response to target-present arrays at electrodes contralateral (solid lines) and ipsilateral (dashed lines) to the side of the target, for the informative cue condition (left) and uninformative cue condition (right). Contralateral ERPs were computed by averaging ERPs obtained in response to left targets at PO8, and to right targets at PO7; ipsilateral ERPs represent averages of ERPs to left targets at PO7, and right targets at PO8. Bottom: ERPs in response to target-absent arrays in the informative cue condition at electrodes contralateral (solid lines) and ipsilateral (dashed lines) to the side of a cued attentional shift.
Figure 4
Figure 4
Difference waveforms obtained by subtracting ERPs at lateral posterior electrodes PO7/8 ipsilateral to the side of a target (for target-present trials), or ipsilateral to the side of a cued attention shift (for target-absent trials), from ERPs at contralateral electrodes. Waveforms are shown separately for target-present trials in the informative cue condition (black solid lines), target-present trials in the uninformative cue condition (dashed lines), and for target-absent trials in the informative cue condition (grey solid lines). The bottom panel shows topographical maps of the difference waveforms obtained in the informative cue condition for target-present and target-absent trials. These maps were constructed by spherical spline interpolation (Perrin, Pernier, Bertrand, & Echallier, 1989) after mirroring the difference waveforms representing the contralaterally enhanced negativity to obtain symmetrical voltages for both hemispheres. Each isocontour line represents a change of 0.6 μV for the target-present maps, and 0.2 μV for the target-absent maps.
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