Synesthesia is a neurological occurrence when one sensory experience automatically triggers another sense. It means “to perceive together” in Greek, indicating two senses that are felt simultaneously. There are many synesthesia examples in psychology. For instance, people with synesthesia, or synesthetes, may smell pears when they hear their own name.
These sense combinations and associations can result in higher sense awareness, heightened creativity, and strong memory recall. Though synesthesia is an irregular sensory processing phenomenon, it is not considered a processing disorder.
There are many different versions of synesthesia that synesthetes may experience. A person may feel one, two, or many different types at any given time. These different synesthesia types can be divided into two main categories: projective synesthesia and associative synesthesia.
As the most common type of synesthesia, projective synesthesia occurs when someone literally sees a color or shape, hears a sound, or feels an object in response to an unrelated stimulus. These sensory associations are persistent across experiences. For example, a person who sees the number 2 as blue will always see it as blue in any context.
Here are some examples of how synesthetes may experience different sensory experiences.
- Chromesthesia: People with chromesthesia (sometimes called “colored hearing”) can see various colors when they hear sounds. They may have a sensation of orange when a car honks or green at the sound of a bird chirping. Composers with synesthesia often see colors associated with specific musical notes. Chromesthesia is one of the most common types of synesthesia.
- Grapheme-Color Synesthesia: Another common form of synesthesia, grapheme-color synesthesia describes the experience of seeing colors associated with letters of the alphabet. These colors may affect how a person “sees” an entire word, as the word could be one color to match the first letter’s color, or each letter may maintain its own color. People with this form of synesthesia can often memorize correct spelling by memorizing a color sequence.
- Lexical-Gustatory Synesthesia: These synesthetes may experience an unrelated taste when they hear a certain word. “Spring” may taste like lemons, while “fancy” may fill their mouth with the taste of spinach.
- Odor-Color Synesthesia: People who can associate smells with visual experiences, particularly colors, have odor-color synesthesia. This type is not as common as other forms.
- Mirror-Touch Synesthesia: People with mirror-touch synesthesia can feel a sensation that they see another person experience, such as a finger prick or hug. This type of synesthesia is common in those with higher levels of empathy.
- Spatial Sequence Synesthesia: If you can see numerical sequences in a particular plane in space, such as in a circle around your head or in hills and valleys, you may have spatial sequence synesthesia. These synesthetes can see sequences either in their minds’ eyes or in their actual vision, making it easier to memorize mathematical facts and historical dates.
- Number Form Synesthesia: This form of synesthesia is related to spatial sequence synesthesia. Instead of seeing numbers in a physical plane, number form synesthetes see a mental map of numbers that they can navigate.
- Auditory-Tactile Synesthesia: Like chromesthesia, people with auditory-tactile synesthesia experience sensory crossover when they hear a sound. These synesthetes may feel a tactile sensation at particular sounds, such as pain in their hands when they hear a whistle. If a strong emotion is triggered by a sound, this could be a form of misophonia, another type of synesthesia.
- Kinesthetic Synesthesia: Related to auditory-tactile synesthesia, kinesthetic synesthesia is connected more to complex relationships (such as mathematical equations or letter sequences).
Associative synesthesia describes a strong association between a stimulus and an unrelated sense. It is not as common as the different types of projective synesthesia described above.
For example, while a person with projective synesthesia may actually smell their mother’s perfume when they hear a violin, someone with associative synesthesia may only feel a strong sense of their mother at the same sound.
Ordinal linguistic synesthesia describes the attribution of personality traits and/or genders to numbers, letters, and colors. It is considered to be a form of associative synesthesia.
Psychologists and neurologists have attempted to study synesthesia with varying levels of success. Because each synesthete’s perception is different, it is difficult to make definitive claims about its origin, causes, and implications. Two famous case studies from the 20th century each studied noted synesthetes in an attempt to learn more about the condition.
Solomon Shereshevsky’s synesthesia enabled him to have a nearly perfect memory. All five of his senses were linked in various ways. His sense associations allowed him to create imaginative mnemonics, but they could also be distracting from a literal sensory experience.
Neuropsychologist Alexander Luria studied Shereshevsky’s synesthetic experiences over a 30-year span in his 1968 book, The Mind of a Mnemonist. The case study prompted a new generation of neurologists and neuropsychologists to look more deeply into synesthesia and memory.
Written by neurologist Richard Cytowic in 1993, The Man Who Tasted Shapes chronicles the experiences of synesthete Michael Watson. It outlines the collaborative experiments that formed Cytowic’s conclusions about synesthesia. The second part of the book reflects on how synesthesia is connected to emotion and what the study of synesthesia could mean for the field of neuroscientific study.
What causes synesthesia? Who is more likely to have it? Check out these interesting facts about synesthesia and famous synesthetes.
- Approximately three to five percent of the population may have some form of synesthesia.
- Synesthesia runs in families. Scientists believe the trait is dominant and could be on the X chromosome.
- No one knows exactly why synesthesia occurs. Some researchers believe it’s a result of an overabundance of neural connections, and that these connections do not limit sensory experiences to one sense. Neural imaging has not provided conclusive results.
- Synesthesia is more prevalent in women than in men, and more common in left-handed people than right-handed people.
- People with synesthesia are considered neurologically typical. However, extreme forms of synesthesia (such as kinesthetic synesthesia) may be associated with the autism spectrum.
- Famous synesthetes in history include artist Vincent Van Gogh, writer Vladimir Nabokov, composer Franz Liszt, and physicist Richard Feynman. Musicians Billy Joel, Mary J. Blige, and Pharrell Williams have also described their experiences with synesthesia.
- You can test your own level of synesthesia with the standard Synesthesia Battery.
Synesthesia can be found in literature and poetry as well. Check out our article on different ways to use synesthetic experience in figurative language and characterization, and read excerpts of famous literary uses of synesthesia.