Aroma chemistry is complex enough, but human beings make matters even more confusing by muddling olfaction with other sensory perceptions. “Scent is a confluence of what we are seeing, hearing, and feeling, emotionally and physically,” Rachel Herz, an expert on the psychology of smell, told. The smell of your grandmother could be a mixture of perfumes she wore, dishes she cooked, and other auditory and visual clues that trigger memories of her.