Perceptual and cognitive task difficulty has differential effects on auditory distraction.

When a task-irrelevant feature of an auditory stimulus varies at rare and unpredictable times, the processing of this change interferes with the processing of task-relevant stimulus information. The present study investigated whether this distraction effect is modulated by the difficulty of the auditory task. Event-related potentials (ERPs) and behavioral responses were recorded while subjects classified stimuli based on their temporal dimension. In one condition, the task was made more difficult by decreasing the perceptual discriminability (temporal distinctiveness) of the stimuli. In a second condition, the difficult task involved an increase in memory load: subjects were asked to assess the duration of the current compared to that of the previous stimulus. The occurrence of an infrequent task-irrelevant change in the pitch of the stimulus caused distraction in all task conditions. Following this change, performance deteriorated, and a distinct P3a component was visible in the ERP. Importantly, the extent of this distraction effect was significantly enhanced during the high memory load task, but not during the difficult perceptual task. It may be that the attentional resources afforded to the stimuli, rather than task difficulty, affected the extent of the distraction response. When the processing requirements of a task demand more highly focused attention for stimulus processing, the processing of the distracting information embedded within this stimulus may inadvertently also benefit from this attention.