Synesthesia: Seeing Sounds and Hearing Colors

Synesthesia (also spelled synaesthesia) is defined as a neurological phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. Although often termed a "neurological condition," synesthesia is not listed in either the DSM-IV or the International Statistical Classification of Diseases and Related Health Problems (ICD) since it most often does not interfere with normal daily functioning. People who report such experiences are known as synesthetes. There are two overall forms of synesthesia: projecting synesthesia and associative synesthesia.

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• Projecting Synesthesia: People who project will see actual colors, forms, or shapes when stimulated, as is commonly accepted as synesthesia.
• Associative Synesthesia: Associators will feel a very strong and involuntary connection between the stimulus and the sense that it triggers.

Some synesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire lives.

Synesthesia literally refers to the fact that in some animals, a stimulus in one sense modality involuntarily elicits a sensation/experience in another sense modality. An example of this would be the taste of lemon visually evoking the color blue. The elicited synesthetic experience does not replace the normal experience but instead always adds to it. Synesthetic elicitations are durable, consistent, and discrete, as noted by Dr. Cytowic.

Estimates for the number of people with synesthesia range from 1 in 200 to 1 in 100,000. There are probably many people who have the condition but do not realize what it is. Synesthesia runs strongly in families, but the precise mode of inheritance has yet to be ascertained. Synesthesia is also sometimes reported by individuals under the influence of psychedelic drugs, after a stroke, during a temporal lobe epilepsy seizure, or as a result of blindness or deafness.

For scientists, synesthesia presents an intriguing problem. Studies have confirmed that the phenomenon is biological, automatic and apparently unlearned, distinct from both hallucination and metaphor. The condition runs in families and is more common among women than men, researchers now know. But until recently, researchers could only speculate about the causes of synesthesia. Now, however, modern behavioral, brain-imaging and molecular genetic tools hold exciting promise for uncovering the mechanisms that drive synesthesia and researchers hope for better understanding how the brain normally organizes perception and cognition.

Types of Synesthesia

Over 60 types of synesthesia have been reported. In one common form of synesthesia, known as grapheme color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored, while in ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities.

In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit precise locations in space (for example, 1970 may be "farther away" than 1980), or may have a (three-dimensional) view of a year as a map.

Yet another recently identified type, visual motion sound synesthesia, involves hearing sounds in response to visual motion and flicker.

Other Types of Synesthesia Include

Neurologist Richard Cytowic identifies the following diagnostic criteria of synesthesia:

• Synesthesia is laden with affect.
• Synesthesia is highly memorable.
• Synesthesia is involuntary and automatic.
• Synesthetic percepts are consistent and generic (i.e., simple rather than pictorial).
• Synesthetic perceptions are spatially extended, meaning they often have a sense of "location." For example, synesthetes speak of "looking at" or "going to" a particular place to attend to the experience.

Synesthetes

• People who report such experiences are known as synesthetes. Most synesthetes report that their experiences are neutral, or even pleasant.
• Synesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire live
• Many people with synesthesia use their experiences to aid in their creative process, and many non-synesthetes have attempted to create works of art that may capture what it is like to experience synesthesia.
• Depending on the study, researchers have suggested 1 in 2,000 people have some form of synesthesia, while others have reported 1 in 300 or even as many as 1 in 23. One problem with statistics is that some individuals will not self-classify as they do not realize that their perceptions are different from those of everyone else.

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Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.