Probability-driven and stimulus-driven orienting of attention to time and sensory modality.

The timing and the sensory modality of behaviorally relevant events often vary predictably, so that it is beneficial to adapt the sensory system to their statistical regularities. Indeed, statistical information about target timing and/or sensory modality modulates behavioral responses-called expectation effects. Responses are also facilitated by short-term repetitions of target timing and/or sensory modality-called priming effects. We examined how the expectation and priming effects on target timing (short vs. long cue-to-target interval) and target modality (auditory vs. visual) interacted. Temporal expectation was manipulated across blocks, while modality expectation was manipulated across participants. Responses were faster when targets were presented at the expected timing and/or in the expected modality in an additive manner, suggesting that temporal and modality expectation operate relatively independently. Similarly, responses were faster when the timing and/or modality of targets was repeated across trials in an additive manner, suggesting that temporal and modality priming operate relatively independently. Importantly, the interactions between expectation and priming were domain specific. In the temporal domain, temporal-expectation effects were observed only when temporal-priming effects were absent. In the modality domain, modality-priming effects predominated for auditory targets whereas modality-expectation effects predominated for visual targets. Thus, the interactions between probability-driven expectation and stimulus-driven priming processes appear to be controlled separately for the mechanisms that direct attention to specific temporal intervals and for the mechanisms that direct attention to specific sensory modalities. These results may suggest that the sensory system concurrently optimizes attentional priorities within temporal and sensory-modality domains.