  Multimodal integration is an important process in perceptual decision-making.
In humans, this process has often been shown to be statistically optimal, or
near optimal: sensory information is combined in a fashion that minimises the
average error in perceptual representation of stimuli. However, sometimes there
are costs that come with the optimization, manifesting as illusory percepts. We
review audio-visual facilitations and illusions that are products of
multisensory integration, and the computational models that account for these
phenomena. In particular, the same optimal computational model can lead to
illusory percepts, and we suggest that more studies should be needed to detect
and mitigate these illusions, as artefacts in artificial cognitive systems. We
provide cautionary considerations when designing artificial cognitive systems
with the view of avoiding such artefacts. Finally, we suggest avenues of
research towards solutions to potential pitfalls in system design. We conclude
that detailed understanding of multisensory integration and the mechanisms
behind audio-visual illusions can benefit the design of artificial cognitive
systems.
