Synesthesia: exploring what smells look like

Arising in around 4.4 percent of people, synesthesia occurs when stimulation of one sense leads to an involuntary experience in another sense (1). By analyzing different odors, researchers in Australia determined that synesthetic experiences depend on identification of the odors and whether or not the odor is likable to the subjects. They also concluded that even when the pathway of odor processing differed – smells can be perceived by both the nose and mouth – identification of the odor was still necessary for a visual experience consistent with the visual experience of the smell (2, 3).

The researchers tested six self-identified odor-color synesthetes. The subjects were first given 20 odors to identify and then illustrated their visual responses either by hand or on a computer program. The subjects also tasted various stimuli, some of which were the same as the odors, and again illustrated their visual response. A group of students that were unaware of the origin of the images evaluated their similarity (3).

When an odor was presented by mouth and then by nose, the images were only similar when both of the stimuli were identified as the same thing. Thus, the researchers concluded that “odor name alone could evoke these complex visual images” (3).

In the absence of identification, there were fewer similarities in the images both across smells and tastes and similarities in the images within each olfactory pathway. In this case, however, how much the subject liked or disliked the odor contributed to how similar the images were (3).

Furthermore, the researchers claim that the “access to meaning drives olfactory synesthetic experiences.” In this case, identification and likability of the stimuli provide meaning, a way for the brain to make sense of the external stimulus. This experiment provides valuable insight to the neurological phenomenon of synesthesia (3).

References:

1. Simner, J., Mulvenna, C., Sagiv, N., Tsakanikos, E., Witherby, S. A., Fraser, C.,…Ward, J. (2006). Synaesthesia: The prevalence of atypical cross-modal experiences. Perception, 35, 1024. doi:10.1068/p5469
2. Ramachandran, V. S., & Hubbard, E. M. (2001). Synaesthesia–a window into perception, thought and language.Journal of consciousness studies,8(12), 3-34.
3. Russell, A., Stevenson, R. J., & Rich, A. N. (2015). Chocolate smells pink and stripy: Exploring olfactory-visual synesthesia.Cognitive neuroscience, (ahead-of-print), 1-12.