Audiovisual integration is preserved in older adults across the cortical hierarchy

Abstract

Effective interactions with the environment rely on integration of multisensory signals: our brains must efficiently combine signals that share a common source, and segregate those that do not. Healthy ageing can change or impair this process. This functional magnetic resonance imaging study assessed the neural mechanisms underlying age differences in the integration of auditory and visual spatial cues. Participants were presented with synchronous audiovisual signals at various degrees of spatial disparity and indicated their perceived sound location. Behaviourally, older adults were able to maintain localisation accuracy, albeit with longer response times. At the neural level, they integrated auditory and visual cues into spatial representations along dorsal auditory and visual processing pathways similarly to their younger counterparts, but showed greater activations in a widespread system of frontal, temporal and parietal areas. According to multivariate Bayesian decoding, these areas encoded critical stimulus information beyond that which was encoded in the brain areas commonly activated by both groups. Surprisingly, however, the boost in information provided by these areas with age-related activation increases was comparable across the two age groups. This dissociation--between comparable response accuracy and information encoded in brain activity patterns across the two age groups, but age-related increases in response times and regional activations--suggests that older participants accumulate noisier sensory evidence for longer, to maintain reliable neural encoding of stimulus-relevant information and thus preserve localisation accuracy.