A Perceptual Oddity Can Help Explain Synesthetic Experiences

Summer is here. We can go to the beach and swim in the nice cool water. The soft water, the cool breeze, and the occasional jellyfish stings are what most of us will experience. But some people, when they swim, have vivid color experiences that vary systematically depending on the swimming style they use.

When they swim breaststroke, they may experience red. When swimming backstroke, they have a vivid experience of green. And so on. This phenomenon is called swimming style synesthesia, strong color experiences when performing, seeing, thinking about or imagining a swimming style—breaststroke, crawl, butterfly, and other strokes.

Swimming style synesthesia is a genuine form of synesthesia. It falls in the wider category of synesthetic experiences. When some people hear a high C note, they experience it as having a certain color. Others may have strong color experiences when touching different things. But there are more surprising forms, for example, lexical-gustatory (strong taste experiences when looking at letters) or spatial time units, sequence-space synesthesia (strong spatial experience when thinking about time units like the days of the week or the months of the year). But swimming style synesthesia poses some important questions about our understanding of synesthesia in general.

In standard cases of synesthesia, the strong color experience is triggered by the sensory input in some other sense modality, like audition or touch. But swimming style synesthesia is different: Here, synesthetic experiences can be triggered in the absence of any kind of perceptual input. It can happen even when you think about a swimming style, with your eyes closed, far away from any body of water.

This makes swimming style synesthesia special. But it also helps us to understand crucial characteristics of synesthesia, namely, that it can be triggered by mental imagery. What triggers the color experiences in swimming style synesthesia? There seem to be two options.

The first option is that when you think about, say, the breaststroke, you involuntarily visualize a person swimming breaststroke and it is this involuntary visual mental imagery of somebody doing breaststroke that triggers the synesthetic experience. And we know that visualizing a synesthesia-inducing sensory input can lead to synesthetic experiences.

The second option is that when you think about breaststroke, you have motor imagery of swimming in breaststroke, you imagine doing the breaststroke. This second option seems to be closer to the subjects’ descriptions of their experience. And in this case, it is motor imagery (imagining doing something) that triggers the synesthetic experience.

It is widely agreed that synesthesia is intricately connected with unusual ways of exercising one’s mental imagery. Synesthetes tend to have more vivid mental imagery. Further, besides introspective reports, there is neuroimaging data that makes this connection. The findings about swimming style synesthesia give us some pointers about the connection between synesthesia and mental imagery. Synesthesia is not a purely perceptual phenomenon: It heavily involves mental imagery.