Enhancement and suppression in a lexical interference fMRI-paradigm

Abstract

Previous picture-word interference (PWI) fMRI-paradigms revealed ambiguous mechanisms underlying facilitation and inhibition in healthy subjects. Lexical distractors revealed increased (enhancement) or decreased (suppression) activation in language and monitoring/control areas. Performing a secondary examination and data analysis, we aimed to illuminate the relation between behavioral and neural interference effects comparing target-related distractors (REL) with unrelated distractors (UNREL). We hypothesized that interference involves both (A) suppression due to priming and (B) enhancement due to simultaneous distractor and target processing. Comparisons to UNREL should remain distractor unspecific even at a low threshold. (C) Distractor types with common characteristics should reveal overlapping brain areas. In a 3T MRI scanner, participants were asked to name pictures while auditory words were presented (stimulus onset asynchrony [SOA] = -200 msec). Associatively and phonologically related distractors speeded responses (facilitation), while categorically related distractors slowed them down (inhibition) compared to UNREL. As a result, (A) reduced brain activations indeed resembled previously reported patterns of neural priming. Each target-related distractor yielded suppressions at least in areas associated with vision and conflict/competition monitoring (anterior cingulate cortex [ACC]), revealing least priming for inhibitors. (B) Enhancements concerned language-related but distractor-unspecific regions. (C) Some wider brain regions were commonly suppressed for combinations of distractor types. Overlapping areas associated with conceptual priming were found for facilitatory distractors (inferior frontal gyri), and areas related to phonetic/articulatory processing (precentral gyri and left parietal operculum/insula) for distractors sharing feature overlap. Each distractor with semantic relatedness revealed nonoverlapping suppressions in lexical-phonological areas (superior temporal regions). To conclude, interference combines suppression of areas well known from neural priming and enhancement of language-related areas caused by dual activation from target and distractor. Differences between interference and priming need to be taken into account. The present interference paradigm has the potential to reveal the functioning of word-processing stages, cognitive control, and responsiveness to priming at the same time.

Keywords: Facilitation; fMRI; inhibition; naming; picture-word interference task; semantic priming; visual object priming; word processing.

Figure 1

Clarification of terms used in the present lexical interference study. The relation between behavioral interference effects, neural interference effects, and underlying cognitive mechanisms is unresolved, as indicated by question marks.

Figure 2

Overview of assumptions on lexical interference in our fMRI-paradigm. The figure depicts the hypotheses A–C and adds previous findings from Abel et al. (2009a) as indicated by asterisks (see also Tab. 1). Priming may occur for both facilitatory (fast naming response) and inhibitory (slow response) distractor types. Especially in brain areas related to conflict processing, enhancement may occur due to more effortful processing (instead of dual activation). REL₁ > REL₂, more activation for a related distractor type 1 (e.g., associative distractors) to another related distractor type 2 (e.g., phonological distractors).

Figure 3

Repetition suppression: areas of significant brain activation (contrasts thresholded at false discovery rate [FDR]P < 0.05 [at least 30 voxels] and masked by the minuend at P < 0.05 uncorrected) when subtracting a related distractor condition from the unrelated distractor condition, rendered onto the lateral and medial surface of a standard brain (see also Table 2).

Figure 4

Repetition enhancement: areas of significant brain activation (contrasts thresholded at uncorrected P < 0.001 [≥5 voxels] and masked by the minuend at P < 0.05 uncorrected) when subtracting the unrelated distractor condition from the phonological (A, B), associative (C), or categorical (D) distractor condition, rendered onto the lateral surface of a standard brain (see also Table 3).

Figure 5

Areas of significant brain activation (conjunction null, threshold at uncorrected P < 0.001, masked with first term at uncorrected P < 0.05) representing the processing of (a) facilitative distractors and (b) distractors with feature overlap, rendered onto the lateral and medial surface of a standard brain (see also Table 4).

Figure 6

Contrast estimates for selected brain regions