Functional characteristics of control adaptation in intermodal sensory processing.

The present work investigated functional characteristics of control adjustments in intermodal sensory processing. Subjects performed an interference task that involved simultaneously presented visual and auditory stimuli which were either congruent or incongruent with respect to their response mappings. In two experiments, trial-by-trial sequential congruency effects were analysed for specific conditions that allowed ruling out "non-executive" contributions of stimulus or response priming to the respective RT fluctuations. In Experiment 1, conflict adaptation was observed in an oddball condition in which interference emanates from a task-irrelevant and response-neutral low-frequency stimulus. This finding characterizes intermodal control adjustments to be based - at least partly - on increased sensory selectivity, which is able to improve performance in any kind of interference condition which shares the same or overlapping attentional requirements. In order to further specify this attentional mechanism, Experiment 2 defined analogous conflict adaptation effects in non-interference unimodal trials in which just one of the two stimulus modalities was presented. Conflict adaptation effects in unimodal trials exclusively occurred for unimodal task-switch trials but not for otherwise equivalent task repetition trials, which suggests that the observed conflict-triggered control adjustments mainly consist of increased distractor inhibition (i.e., down-regulation of task-irrelevant information), while attributing a negligible role to target amplification (i.e., enhancement of task-relevant information) in this setup. This behavioral study yields a promising operational basis for subsequent neuroimaging investigations to define brain activations and connectivities which underlie the adaptive control of attentional selection.