The “crossing of senses,” in perception and memory, was once considered too strange to study. Now scientists suspect it’s universal, at least in infancy.
Question: What is the nature of synesthetic memory?
Siri Hustvedt: Well there's speculation, and it may be a little more than speculation now, that infants are synesthetes, and synesthesia is simply a crossing of two senses. It's almost like a translation of one sense into another. Famous examples are people who see numbers as colors. Every number has a distinct color. Synesthetes don't agree on which color. But when a "7," for example, for some people is always green. I do not have that kind of synesthesia, but in a way I think many of us have that when we read. You know, when I read a book, I'm always seeing the people. I'm making mental images to accompany it. So that I'm translating the sight of those little characters on the page into visual images that I can take with me and keep.
I was rather amused to read, during my research for this book, about something called "Mirror Touch Synesthesia" and saying to myself, "Well, I have that." And so that is when people look at someone. Something is happening to another person. Say you look at someone being slapped on the arm. And then the mirror touch synesthete has a sensation in the arm. Not the same as being slapped, at least not in my case at all. But there is a kind of mirroring experience so that the visual looking becomes the tactile impression in the body. And I think you see it again going back to behaviorism and talk of it. Before brain scans and before recent research into the brain, people were very reluctant to do any studies about synesthesia because it just seemed so wacky. And so that's what happens. Once researchers have some kind of hypothesis about neural networks in the brain and maybe that infants are all synesthetes and that as the brain develops and as its plasticity continues, most people lose that crossing over of one sense to the other, and some people don't. They retain it.