What makes synesthesia such a powerful lecture topic in the Intro Psych sensation and perception chapter is that it’s a beautiful illustration of how our experience is merely a representation, and just one representation, of the world around us.
The neuroscientist David Eagleman provides a nice introduction to synesthesia in this two and a half minute video.
Years ago in class, after I concluded my lecture on synesthesia, a young woman in the back of the room raised her hand. She said she didn’t know her experience of the world was different from everyone else’s until a friend of hers took my class a year earlier. She said a group of them were standing around when he started talking about this cool thing called synesthesia that he learned about that day in his Intro Psych course. He explained that the most common form is seeing sounds where sounds produce color, like a filter has been applied to vision. My current student said to her friends, “Doesn’t everybody experience that?” They all stopped and looked at her. At the age of 18, she learned that she was a synesthete.
I made the same error once in class. After talking about synesthesia, I said it’s like when you’re drifting off to sleep and a sudden noise causes a black and white pattern to flash in your vision – sound produces a visual sensation. My students looked at me blankly. Apparently I was the only one with such an experience. My visual experience used to happen pretty regularly, probably a few times a week, but now it’s a rare occurrence, probably once every few months. In any case, I learned that it’s non-existent in many, at least amongst my students that term.
I suppose this assumption is a kind of extension of the false consensus effect. We not only assume that others share our beliefs and attitudes, but that others share our sensory experiences.
There is research evidence that suggests we are all born synesthetes (see for example Wagner and Dobkins, 2011), and as we mature through infancy and childhood our senses begin to specialize, much like how infants can produce sounds used in all languages only to become specialists in their native language or languages as they develop.
Exploring vision in non-human animals helps students appreciate that their own sensory experiences may be very different from others.
For example, dogs have two kinds of cones in their retinas; they detect yellow and blue. That may make them roughly equivalent to humans who have red-green color blindness (Wolchover, 2012).
And birds? They have four kinds of cones, the fourth allows them to see ultraviolet light. It’s been posited that the ability to see UV light allows some songbirds to better see each other as their plumage glows with UV light and that raptors can better track prey that leave a urine trail that also glows with UV light. There’s reason to believe that the jury is still out on both of those hypotheses (see for example, Lind, et.al., 2013). Both are given though in this rapid-fire 4-minute SciShow on what birds see.
And what about infrared light? While the human eye can’t see it, our digital cameras can. Turn on your cellphone camera and direct it at the end of your TV remote, the end you point toward your TV. Press and hold the "on" button on your remote. You’ll see the light through your phone’s camera even though your naked eye can't see it. This is also the easiest way to determine whether you need to change the batteries in your remote or whether it's just your dog standing in front of the TV’s receiver.
For a short in-class next-day assignment – or same-day assignment, if your students have in-class internet access – or for an online discussion board assignment, invite students to research other individual differences in human sensation or differences in sensory experiences between humans and other animals. In class, students can share in small groups, and then invite volunteers to share the most interesting things they found. Ask students to identify the site where they found the information and why they believe the site is a reputable source.
Lind, O., Mitkus, M., Olsson, P., & Kelber, A. (2013). Ultraviolet sensitivity and colour vision in raptor foraging. Journal of Experimental Biology, 216(19), 3764-3764. doi:10.1242/jeb.096123
Wagner, K., & Dobkins, K. R. (2011). Synaesthetic associations decrease during infancy. Psychological Science, 22(8), 1067-1072. doi:10.1177/0956797611416250
Wolchover, N. (2012, June 26). How do dogs see the world? Retrieved from http://www.livescience.com/34029-dog-color-vision.html