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An important question concerning inter-areal communication in the cortex is whether these interactions are synergistic, i.e. convey information beyond what can be performed by isolated signals. In other words, any two signals can either share common information (redundancy) or they can encode complementary information that is only available when both signals are considered together (synergy). Here, we dissociated cortical interactions sharing common information from those encoding complementary information during prediction error processing. To this end, we computed co-information, an information-theoretical measure that distinguishes redundant from synergistic information among brain signals. We analyzed auditory and frontal electrocorticography (ECoG) signals in five common awake marmosets performing two distinct auditory oddball tasks, and investigated to what extent event-related potentials (ERP) and broadband (BB) dynamics exhibit redundancy and synergy for auditory prediction error signals. We observed multiple patterns of redundancy and synergy across the entire cortical hierarchy with distinct dynamics. The information conveyed by ERPs and BB signals was highly synergistic even at lower stages of the hierarchy in the auditory cortex, as well as between lower and higher areas in the frontal cortex. These results indicate that the distributed representations of prediction error signals across the cortical hierarchy can be highly synergistic.

Multisensory stimulation is associated with behavioural benefits, including faster processing speed, higher detection accuracy, and increased subjective awareness. These effects are most likely explained by multisensory integration, alertness, or a combination of the two. To examine changes in subjective awareness under multisensory stimulation, we conducted three experiments in which we used Continuous Flash Suppression to mask subthreshold visual targets for healthy observers. Using the Perceptual Awareness Scale, participants reported their level of awareness of the visual target on a trial-by-trial basis. The first experiment had an audio-visual Redundant Signal Effect paradigm, in which we found faster reaction times in the audio-visual condition compared to responses to auditory or visual signals alone. In two following experiments, we separated the auditory and visual signals, first spatially (experiment 2) and then temporally (experiment 3), to test whether the behavioural benefits in our multisensory stimulation paradigm could best be explained by multisensory integration or increased phasic alerting. Based on the findings, we conclude that the largest contributing factor to increased awareness of visual stimuli accompanied by auditory tones is a rise in phasic alertness and a reduction in temporal uncertainty with a small but significant contribution of multisensory integration.