Impact of conflict expectation on selective attention and action selection processes during motor decisions: an EEG study

Any behavior emerges from a competition between potential options, occurring at both the sensory and motor levels. At the sensory level, selective attention is thought to bias competitive interactions by favoring neural activity related to goal-relevant sensory information. At the motor level, control processes help ensure that activity related to the most beneficial action reaches a selection threshold, while keeping irrelevant alternatives away from it. At the behavioral level, conflictual stimuli lengthen reaction times and reduce accuracy, probably because they increase load on both sensorimotor processes. However, the presence of statistical regularities in the occurrence of conflict can attenuate the cost of incongruent stimuli, an effect that has been related to the recruitment of additional cognitive control processes. Here, we investigated the impact of conflict expectation on selective attention and action selection processes. Healthy subjects (n=17) performed a Flanker task in which they were asked to indicate by a left or right button-press the orientation of a briefly presented left- or right-facing central arrow, flanked by a set of two distractor arrows on each side which either pointed in the same (congruent trials) or in the opposite direction (incongruent trials). The percentage of congruent and incongruent trials was manipulated in separate blocks to produce two different contexts in terms of conflict expectation. In mostly congruent blocks (MCB; low conflict expectation), 80% of the trials were congruent; the reversed proportion was used in the mostly incongruent blocks (MIB; high conflict expectation), with 80% of trials involving incongruent stimuli. Selective attention and action selection were assessed in both contexts by recording steady-state visual evoked potentials (SSVEPs, central and distractor arrows flickered at different frequencies) and response-locked potentials measured over the ipsilateral and contralateral motor cortices (with respect to the responding hand), respectively. As expected, subjects made more errors and responded slower in incongruent than in congruent trials. This behavioral cost of conflict was particularly marked in contexts where incongruent trials were unlikely (MCB) compared to when they were expected (MIB). At the sensory level, we observed higher target-related SSVEP amplitudes in MCB compared to MIB, indicating that subjects focused more on the target when conflict was unlikely. At the motor level, ipsilateral response-locked potentials were of smaller amplitude in MCB compared to MIB, especially in incongruent trials, suggesting less irrelevant motor activity when conflict was unlikely. Interestingly, the more subjects focused on the target, the smaller the ipsilateral activity. These findings suggest that a stronger attentional focus on the target helps reduce ipsilateral motor activity and that this strategy is mostly used when conflictual signals may occur in a non-predictive manner