Kids or adults with sensory processing difficulties overload easily with sight, sound, touch, and smells. In this very basic research paper, researchers show that smells are identified with visual cues. If you take visual cues away, it much more difficult to distinguish different odors.
It's because the senses are so closely linked to each other that it's easy to upset other sensory when one type of 'sensory' input goes awry. It means that a child with auditory processing problems might develop visual overload problems (e.g. highly distractible) or a child with proprioceptive sensory problems might be overly sensitive to smells, etc.
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More Sensory Integration: The Color of Smells