Effects of lateralized cues on the processing of lateralized auditory stimuli

We examined the influence of auditory spatial cues on the processing of subsequently presented lateralized auditory target stimuli. In three experiments, effects of the position of the cue on event-related potentials (ERPs) and reaction times (RTs) to the target, which could occur at the same or at a different position to the cue, were examined. In Experiments I and II, stimulus-pairs were delivered via loudspeakers 13 degrees to the right or left of fixation. The cue was task-irrelevant in the sense that it never required a response, whereas the target was task-relevant. In Experiment I, the cue was not informative about the position of the succeeding target, that is, the target was presented at the same or at a different position to the cue with equal probability. In Experiment II, the cue predicted a target with high validity, occurring at the position opposite to the cue. In both experiments, the ERPs to targets presented at the same position as the preceding cue were negatively modulated compared with the ERPs to targets presented at a different position. This negative difference (Nd) between the ERPs to same and different position stimuli occurring between 200-300 ms relative to target onset was also obtained in situations where no overt behavior was required. Effects of cue position on RTs to the target were only observed in Experiment II, being shorter for validly predicted targets. These Nd effects either reflect refractoriness of location-specific exogeneous ERP components or involuntary attentional selection. In order to decide between these alternatives, a third experiment was performed, in which stimulus-pairs were presented via headphones to the left and right ear in attend and ignore condition. An Nd effect was obtained in the attend condition only. The absence of Nd effects in the ignore condition suggests that the Nd obtained in attend condition cannot completely be explained by refractoriness of exogeneous ERP components and thus reflects attentional processes.