Dual mechanisms for the cross-sensory spread of attention: how much do learned associations matter?

The spread of attention-related processing across anatomically separated cortical regions plays an important role in the binding of an object's features, both within and across sensory modalities. We presented multiple exemplars of semantically congruent multisensory objects (e.g., dogs with barks) and semantically incongruent multisensory objects (e.g., guitars with barks) while recording high-density event-related potentials and tested whether highly learned associations among the multisensory features of well-known objects modulated the spread of attention from an attended visual stimulus to its paired, task-irrelevant sound. Our findings distinguish dual mechanisms for the cross-sensory spread of attention: 1) a stimulus-driven spread of attention that occurs whenever a task-irrelevant sound is simultaneously presented with an attended visual stimulus, independent of highly learned associations, and 2) a representation-driven spread of attention that occurs in response to a task-irrelevant sound that is semantically congruent with a visual target and is therefore dependent on highly learned associations. The first mechanism is thought to reflect bottom-up feature binding, whereas the second mechanism is thought to reflect the top-down activation of a stored object representation that includes the well-known object's multisensory features. When a semantically congruent, task-irrelevant sound is simultaneously presented with a well-known visual target, the combined spread of attention through both mechanisms appears additive.