The impact of attentional demand on the motor interference effect induced by dangerous stimuli

The mechanisms by which attentional demand modulates the motor interference effect induced by dangerous stimuli remain debated. To test the competing predictions of the limited capacity theory and the signal suppression hypothesis, we manipulated attentional demand (low vs. high) and interfering stimulus type (high-arousal dangerous, medium-arousal dangerous, low-arousal neutral) within a Go/NoGo task combined with an additional singleton paradigm. Twenty-five healthy participants were recruited; after applying the a priori exclusion criterion, 24 were retained for analysis. Under low attentional demand, reaction times (RTs) did not differ across interfering stimulus types. Under high attentional demand, RTs were significantly longer for high-arousal dangerous stimuli than for low-arousal neutral stimuli and were marginally longer for medium-arousal dangerous stimuli than for low-arousal neutral stimuli. Error rates did not differ significantly across interfering stimulus types under either attentional-demand condition. The RT pattern was consistent with greater interference from more arousing dangerous stimuli under high attentional demand. These findings are consistent with the signal suppression hypothesis: when attentional resources are sufficient, task-irrelevant dangerous stimuli may be more effectively suppressed; when resources are taxed by a demanding primary task, suppression may be compromised, allowing dangerous stimuli greater access to task processing. However, attentional demand covaried with target stimulus type, so the observed interaction cannot be attributed to attentional demand alone; the equiprobable Go/NoGo design likewise precludes conclusions about motor inhibitory control. Boundary conditions and alternative interpretations are discussed.