Spatial attention (i.e., task-relevance) and expectation (i.e., signal probability) are two critical top-down mechanisms guiding perceptual inference. Spatial attention prioritizes processing of information at task-relevant locations. Spatial expectations encode the statistical structure of the environment. An unresolved question is how the brain allocates attention and forms expectations in a multisensory environment, where task-relevance and signal probability over space can differ across sensory modalities. We used functional magnetic resonance imaging in human participants (female and male) to investigate whether the brain encodes task-relevance and signal probability over space separately or interactively across sensory modalities. In a novel multisensory paradigm, we manipulated spatial attention and expectation selectively in audition and assessed their effects on behavioral and neural responses to auditory and visual stimuli. Our results show that both auditory and visual stimuli increased activations in a right-lateralized frontoparietal system, when they were presented at locations that were task-irrelevant in audition. Yet, only auditory stimuli increased activations in the medial prefrontal cortex when presented at expected locations and in audiovisual and frontoparietal cortices signaling a prediction error when presented at unexpected locations. This dissociation in multisensory generalization for attention and expectation effects shows that the brain controls attentional resources interactively across the senses but encodes the statistical structure of the environment as spatial expectations independently for each sensory system. Our results demonstrate that spatial attention and expectation engage partly overlapping neural systems via distinct mechanisms to guide perceptual inference in a multisensory world.In our natural environment the brain is exposed to a constant influx of signals through all our senses. How does the brain allocate attention and form spatial expectations in this multisensory environment? Because observers need to respond to stimuli regardless of their sensory modality, they may allocate attentional resources and encode the probability of events jointly across the senses. This psychophysics and neuroimaging study shows that the brain controls attentional resources interactively across the senses via a frontoparietal system but encodes the statistical structure of the environment independently for each sense in sensory and frontoparietal areas. Thus, spatial attention and expectation engage partly overlapping neural systems via distinct mechanisms to guide perceptual inference in a multisensory world.

No abstract

Attention (i.e., task relevance) and expectation (i.e., signal probability) are two critical top-down mechanisms guiding perceptual inference. Attention prioritizes processing of information that is relevant for observers’ current goals. Prior expectations encode the statistical structure of the environment. Research to date has mostly conflated spatial attention and expectation. Most notably, the Posner cueing paradigm manipulates spatial attention using probabilistic cues that indicate where the subsequent stimulus is likely to be presented. Only recently have studies attempted to dissociate the mechanisms of attention and expectation and characterized their interactive (i.e., synergistic) or additive influences on perception. In this review, we will first discuss methodological challenges that are involved in dissociating the mechanisms of attention and expectation. Second, we will review research that was designed to dissociate attention and expectation in the unisensory domain. Third, we will review the broad field of crossmodal endogenous and exogenous spatial attention that investigates the impact of attention across the senses. This raises the critical question of whether attention relies on amodal or modality-specific mechanisms. Fourth, we will discuss recent studies investigating the role of both spatial attention and expectation in multisensory perception, where the brain constructs a representation of the environment based on multiple sensory inputs. We conclude that spatial attention and expectation are closely intertwined in almost all circumstances of everyday life. Yet, despite their intimate relationship, attention and expectation rely on partly distinct neural mechanisms: while attentional resources are mainly shared across the senses, expectations can be formed in a modality-specific fashion.