Synesthesia can occur between any combination of senses or cognitive pathways.
Synesthesia can occur between any combination of senses or cognitive pathways.

Synesthesia is termed as a perceptual condition in which the stimulation of one sensory or cognitive pathway triggers an automatic, involuntary (beyond conscious control) experience involving several other senses. The senses tend to intertwine giving an additional dimension to the persons’ perception of the world. Synesthesia is rare. It is a genetically linked trait estimated to affect only 5% of the general population. People who experience this during their lifetime are termed synesthetes; they tend to visualize numbers or music as colors, taste words, or feel a sensation on their skin when they smell certain scents. They may also see abstract concepts, such as time projected in the space around them.

What causes synesthesia?

Synesthesia can occur between any combination of senses or cognitive pathways. They are believed to be caused by two different possibilities. Different regions of the brain are specialized to perform their defined functions. In synesthesia, there is increased crosstalk between regions specialized for different functions. This results in different types of synesthesia. Also, it is believed to have been inherited due to the disinhibited feedback mechanism or a reduction in the amount of inhibition along normally existing feedback pathways. Synesthesia can also be acquired temporarily due to the use of psychedelic drugs, alcohol, and caffeine.

What are the types of synesthesia?

Synesthesia is an anomalous blending of the senses in which the stimulation of one modality simultaneously produces sensation in a different modality. At least 60 different types of synesthesia are recognized to occur in humans. Most people with the condition experience at least two types of synesthesia. The most common type is grapheme-color synesthesia, in which letters or numbers are visualized to be colored.

Some other types include:

  • Smelling certain scents when hearing certain sounds.
  • Seeing music as colors in the air (music-color synesthesia).
  • Tasting words (lexical-gustatory synesthesia).
  • Feeling certain textures causes certain emotions (tactile-emotion synesthesia).
  • Feeling that time has a physical characteristic (time-space synesthesia).
  • Seeing a certain color when feeling pain.
  • Seeing sign language as colors.

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What are the signs and symptoms of synesthesia?

Synesthesia is believed to be caused by an overabundance of neuronal connections in the brain. There are multiple types of synesthesia all with different symptoms. A person may have only one type of synesthesia or a combination of a few kinds. The common symptoms include:

  • Involuntary perceptions that cross over between senses (tasting shapes, hearing colors, etc.)
  • Sensory triggers that consistently and predictably cause interplay between senses (e.g., every time on seeing the letter A, they see it in red).
  • Ability to describe their unusual perceptions to other people.

How is synesthesia diagnosed?

There are no specific guidelines for diagnosing synesthesia. People with synesthesia are typically diagnosed based on the following criteria:

  • Involuntarily experience their perceptions.
  • Project sensations outside the mind, such as seeing colors floating through the air when they hear sounds.
  • Have a perception that is the same each time.
  • Have a generic perception, such as seeing a shape in response to a certain smell but not seeing something more complex.
  • The secondary synesthetic perception is better than the primary perception for them.
  • Have emotional reactions, such as pleasurable feelings, linked to their perceptions.

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Medically Reviewed on 3/26/2021
References
Science Direct. Synesthesia. https://www.sciencedirect.com/topics/neuroscience/synesthesia

Carpenter S. Everyday Fantasia: The World of Synesthesia. Monitor on Psychology. March 2001; 32(3). https://www.apa.org/monitor/mar01/synesthesia

Brang D, Ramachandran VS. Survival of the synesthesia gene: why do people hear colors and taste words? PLoS Biol. 2011;9(11):e1001205. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3222625/you