Unpredictability impairs goal-directed target processing and performance

Unpredictability influences emotion and attention, but its effects on goal-directed behavior are unclear. We examined whether unpredictable events interfere with performance, using event-related potentials to specify underlying attentional dynamics. The paradigm involved task-irrelevant distracters of either predictable or unpredictable content (neutral/negative) preceding targets of a stimulus discrimination task. Mean and single-trial analyses showed that unpredictable compared to predictable distracters elicited larger late positive potential (LPP) amplitudes and were followed by diminished P300 amplitudes and slower responses to the target. Single-trial distracter LPP mediated the trial-wise effect of unpredictable distracters on target P300. Diminished single-trial target P300 predicted slower response times, but we did not observe mediation; distracter LPP was also unrelated to behavior. These findings suggest that unpredictability impairs target processing and performance. Diminished target processing appears to result from distracters and targets competing for limited attentional resources and behavioral output is directly related to attentional engagement with the target.