Abstract
Sounds can modulate visual perception as well as neural activity in retinotopic cortex. Most studies in this context investigated how sounds change neural amplitude and oscillatory phase reset in visual cortex. However, recent studies in macaque monkeys show that congruence of audio-visual stimuli also modulates the amount of stimulus information carried by spiking activity of primary auditory and visual neurons. Here, we used naturalistic video stimuli and recorded the spatial patterns of functional MRI signals in human retinotopic cortex to test whether the discriminability of such patterns varied with the presence and congruence of co-occurring sounds. We found that incongruent sounds significantly impaired stimulus decoding from area V2 and there was a similar trend for V3. This effect was associated with reduced inter-trial reliability of patterns (i.e. higher levels of noise), but was not accompanied by any detectable modulation of overall signal amplitude. We conclude that sounds modulate naturalistic stimulus encoding in early human retinotopic cortex without affecting overall signal amplitude. Subthreshold modulation, oscillatory phase reset and dynamic attentional modulation are candidate neural and cognitive mechanisms mediating these effects.
Highlights
Perception of the environment requires integration of sensory information across the senses, but how our brains combine information from different sensory streams is still poorly understood
The resulting accuracy contrast maps were normalised to MNI space and tested for whole brain family-wise error (FWE) corrected significance at cluster level in SPM 8
Significant clusters were identified anatomically using the Juelich Histological Atlas implemented in the SPM Anatomy Toolbox (v. 1.8, http://www.fz-juelich.de/inm/inm-1/ DE/Forschung/_docs/SPMAnatomyToolbox/SPMAnatomyToolbox_node. html)
Summary
Perception of the environment requires integration of sensory information across the senses, but how our brains combine information from different sensory streams is still poorly understood. The past decade has seen new anatomical and functional evidence for multisensory interactions even at the level of primary sensory areas (see Driver and Noesselt, 2008; Klemen and Chambers, 2012 for an overview). There are direct feedback connections from primary auditory and multisensory areas to V1 and V2 in macaque (Clavagnier et al, 2004; Falchier et al, 2002; Rockland and Ojima, 2003) and similar connections in rodents (Allman et al, 2008; Budinger et al, 2006). Some bimodal neurons can be found even in primary sensory areas Recent evidence from cats and rodents points to subthreshold modulation of ‘unimodal’ visual neurons
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