Item-Specific Proportion Congruency Uncovers Different Forms of Attentional Control: An event-related fNIRS Study

Recent research has shown that attentional control can be modulated at the item-specific level, meaning that different control strategies can be applied to individual stimuli based on their relative frequencies within a given set. However, an alternative account suggests these findings may be confounded by stimulus-response contingency learning. Contingency is the proportion of trials where a distractor appears with its corresponding target; higher contingency enables faster associative response preparation, producing behavioral effects that mimic item-specific control. While neuroimaging studies provide some evidence for anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (dLPFC) involvement during controlled processes, differentiating item-specific control from contingency learning at the neural level remains challenging. In particular, no prior study has examined how temporal factors influence prefrontal engagement during these two processes.

This study utilized item-specific proportion congruency (ISPC) manipulation via the flanker task. Hemodynamic activity in the prefrontal cortex was measured using functional near-infrared spectroscopy (fNIRS) alongside reaction time and error rates. The role of contingency learning was examined by manipulating stimulus onset asynchrony (SOA). A 2 (congruency) × 2 (proportion congruency) × 3 (SOA: -250, 0, +250 ms) within-subject design with repeated-measures ANOVA was used. To control for multiple comparisons across the 16 channels and 7 ANOVA effects, a hierarchical false discovery rate (FDR) procedure was applied.

The ISPC effect was significant and modulated by SOA, being significant at -250 and 0 ms but not at +250 ms. In fNIRS data, the SOA main effect was significant in eight channels (3,9-14,16), and the ISPC effect was significant in four channels (1, 10, 11, and 12), after hierarchical FDR correction. The three-way interaction was not significant in any channel. Contingency analysis revealed a main effect, with the largest contingency effect at -250 ms. The fNIRS contingency main effect was also significant in channels 1, 10, 11, and 12.

While behavioral results mostly support contingency learning, fNIRS data revealed ISPC-related activation in prefrontal channels with sensitivity to BA 46 (lateral, channel 1) and the BA 10/BA 11 overlap zone (medial, channels 10-12), with channel 11 emerging as a convergence point for both SOA and ISPC effects. This spatial dissociation is consistent with the possible involvement of both control and learning processes operating in parallel within distinct prefrontal subregions.