The effect of feature-based attention on flanker interference processing: An fMRI-constrained source analysis

Abstract

The present study examined whether feature-based cueing affects early or late stages of flanker conflict processing using EEG and fMRI. Feature cues either directed participants' attention to the upcoming colour of the target or were neutral. Validity-specific modulations during interference processing were investigated using the N200 event-related potential (ERP) component and BOLD signal differences. Additionally, both data sets were integrated using an fMRI-constrained source analysis. Finally, the results were compared with a previous study in which spatial instead of feature-based cueing was applied to an otherwise identical flanker task. Feature-based and spatial attention recruited a common fronto-parietal network during conflict processing. Irrespective of attention type (feature-based; spatial), this network responded to focussed attention (valid cueing) as well as context updating (invalid cueing), hinting at domain-general mechanisms. However, spatially and non-spatially directed attention also demonstrated domain-specific activation patterns for conflict processing that were observable in distinct EEG and fMRI data patterns as well as in the respective source analyses. Conflict-specific activity in visual brain regions was comparable between both attention types. We assume that the distinction between spatially and non-spatially directed attention types primarily applies to temporal differences (domain-specific dynamics) between signals originating in the same brain regions (domain-general localization).

Figure 1

Types of trials with timing from EEG sessions. Following a jittered intertrial interval, upcoming stimulus colour was cued (red, green, uninformative). After the interstimulus interval Flanker stimuli were presented either in green or red above or below fixation. Participants responded to the identity of the central letter. Top: Neutral cueing; Middle: Invalid cueing; Bottom: Valid cueing.

Figure 2

Flanker processing group fMRI activation (N = 21). Rendered activation clusters of the contrast incongruent > congruent with invalid (blue) and valid cueing (red). Bars indicate t-values (p < 0.001; k ≥ 10). ACC, anterior cingulate gyrus; ANG, angular gyrus; INS, insula; IPL, inferior parietal lobule; MFG, middle frontal gyrus; MoFG, middle orbitofrontal gyrus; OPERC, operculum; PCU, precuneus; PrCG, precentral gyrus; SMA, supplementary motor area; SMG, supramarginal gyrus.

Figure 3

Grand average ERPs and difference waves (DW) for flanker interference (stimulus-locked: –200 to 900 ms). Congruent and incongruent conditions are shown with valid (left), neutral (middle) and invalid (right) cueing at electrode positions Cz (top) and PO7 (bottom). Difference waves are denoted below the grand averages (N = 21).

Figure 4

Locations and source waveforms of regional sources for flanker interference (N = 21). Middle: locations of the regional sources in right lingual gyrus, left anterior cingulate gyrus, left inferior frontal gyrus, and left precentral gyrus projected onto the Talairach-transformed MNI brain. Root mean square source waveforms are shown for each regional source and condition (0–900 ms). Congruent conditions are presented in green, incongruent conditions in red. Below the source waveforms difference waves are shown in the respective colour of the regional source. The BCa bootstrap 95%-confidence interval is depicted as a grey area surrounding the difference waves. Epochs deviating from zero for > 20 ms are considered significant and coloured in green (congruent > incongruent) and red (incongruent > congruent). L = left hemisphere; R = right hemisphere.

Figure 5

Group fMRI activation for flanker interference with spatial and feature-based cueing. Rendered activation clusters of the contrast incongruent > congruent with spatial (red; N = 19) and feature-based cueing (blue; N = 21). Bars indicate t-values (p < 0.001; k ≥ 10). ACC, anterior cingulate gyrus; FEF, frontal eye field; MFG, middle frontal gyrus; MOG, middle occipital gyrus; PCU, precuneus; SPL, superior parietal lobule; TPJ, temporoparietal junction.