Attention switching and patterns of sound locations in counting clicks.

The present study investigates the process of auditory attention switching by means of experiments in which observers counted the number of monaurally and interaurally presented clicks. Several studies have reported that the number of interaurally presented events was underestimated relative to monaurally presented ones. Ten Hoopen and Vos, however, could not replicate this phenomenon. The data from Experiment 1 demonstrate that such a discrepancy is caused by the different orders in which the monaural and interaural sequences were presented. With blocked presentation, interaural sequences were counted less well than monaural sequences, whereas there was no difference when all sequence types were randomized. An attention-switching mechanism was proposed to account for performance on interaural sequences during blocked presentation. In the random case observers presumably did not switch their attention to and fro, but "multiplexed" the channels. Experiment 2 investigated whether observers can deliberately suppress the process of attention switching when confronted with blocked interaural sequences. The results show that they cannot, which suggests that attention switching is an automatic process.