Potential sources of multisensory influences on low-level sensory cortices include direct projections from sensory cortices of different modalities, as well as more indirect feedback inputs from higher order multisensory cortical regions. These multiple architectures may be functionally complementary, but the exact roles and inter-relationships of the circuits are unknown. We tested the propositions that: 1) Feedforward and lateral pathways subserve speed functions, such as fast detection of potentially dangerous objects approaching in the periphery. Multisensory integration effects in this context are predicted in peripheral fields of low-level sensory cortices. 2) Slower feedback pathways underpin accuracy functions, such as discrimination or identification of complex sensory inputs. Integration effects in this context are predicted in higher-order association cortices and central/foveal fields of low-level sensory cortex. We used functional magnetic resonance imaging to compare the effects of central versus peripheral stimulation on audiovisual integration, while varying speed and accuracy requirements for behavioral responses. We found that task demands and stimulus eccentricity interact in low-level cortices in more complex ways than predicted by the simple dichotomy of peripheral/speed and foveal/accuracy functions. Interestingly, different task requirements yielded seemingly qualitatively different integration processes in visual versus auditory cortex. Additionally, our findings point to individual differences in integration that may be related to skills and strategy. Overall, these findings suggest that instead of using fixed, specialized pathways, the exact circuits and mechanisms that are used for low-level multisensory integration are much more flexible and contingent upon both individual and contextual factors than previously assumed.

audiovisual; low-level integration; contextual control; fMRI; task demand; eccentricity