Synesthesia

For other uses, see Synesthesia (disambiguation).

This article is about the perceptual phenomenon. For the MIDI keyboard program, see Synthesia.

Synesthesia

Other names Synaesthesia[1][2]

Synæsthesia, synaesthesia

How someone with synesthesia might perceive certain letters and numbers. Synesthetes see characters just as others do (in whichever color actually displayed) but may simultaneously perceive colors as associated with or evoked by each one.

Specialty Psychiatry, neurology

Synesthesia is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway.[3][4][5][6] People who report a lifelong history of such experiences are known as synesthetes. Awareness of synesthetic perceptions varies from person to person.[7]

In one common form of synesthesia, known as grapheme-color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored.[8][9] In spatial-sequence, or number form synesthesia, numbers, months of the year, or days of the week elicit precise locations in space (for example, 1980 may be "farther away" than 1990), or may appear as a three-dimensional map (clockwise or counterclockwise).[10][11] Synesthetic associations can occur in any combination and any number of senses or cognitive pathways.[12] Little is known about how synesthesia develops. It has been suggested that synesthesia develops during childhood when children are intensively engaged with abstract concepts for the first time.[13] This hypothesis – referred to as semantic vacuum hypothesis – explains why the most common forms of synesthesia are grapheme-color, spatial sequence and number form. These are usually the first abstract concepts that educational systems require children to learn.

Difficulties have been recognized in adequately defining synesthesia.[14][15] Many different phenomena have been included in the term synesthesia ("union of the senses"), and in many cases the terminology seems to be inaccurate. A more accurate but less common term may be ideasthesia.

The earliest recorded case of synesthesia is attributed to the Oxford University academic and philosopher John Locke, who, in 1690, made a report about a blind man who said he experienced the color scarlet when he heard the sound of a trumpet.[16] However, there is disagreement as to whether Locke described an actual instance of synesthesia or was using a metaphor.[17] The first medical account came from German physician, Georg Tobias Ludwig Sachs in 1812.[17][18][19] The term is from the Ancient Greek σύν syn, "together", and αἴσθησις aisthēsis, "sensation".[16]

There are two overall forms of synesthesia:

projective synesthesia: people who see actual colors, forms, or shapes when stimulated (the widely understood version of synesthesia).
associative synesthesia: people who feel a very strong and involuntary connection between the stimulus and the sense that it triggers.

For example, in chromesthesia (sound to color), a projector may hear a trumpet, and see an orange triangle in space, while an associator might hear a trumpet, and think very strongly that it sounds "orange".[citation needed]

Synesthesia can occur between nearly any two senses or perceptual modes, and at least one synesthete, Solomon Shereshevsky, experienced synesthesia that linked all five senses.[medical citation needed] Types of synesthesia are indicated by using the notation x → y, where x is the "inducer" or trigger experience, and y is the "concurrent" or additional experience. For example, perceiving letters and numbers (collectively called graphemes) as colored would be indicated as grapheme → color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated as tone → (color, movement) synesthesia.

While nearly every logically possible combination of experiences can occur, several types are more common than others.

Grapheme-color synesthesia

Main article: Grapheme-color synesthesia

From the 2009 non-fiction book Wednesday Is Indigo Blue.[5] Note this example's upside-down clock face.

In one of the most common forms of synesthesia, individual letters of the alphabet and numbers (collectively referred to as graphemes) are "shaded" or "tinged" with a color. While different individuals usually do not report the same colors for all letters and numbers, studies with large numbers of synesthetes find some commonalities across letters (e.g. A is likely to be red).[20]

Chromesthesia

Main article: Chromesthesia

Another common form of synesthesia is the association of sounds with colors. For some, everyday sounds such as doors opening, cars honking, or people talking can trigger seeing colors. For others, colors are triggered when musical notes or keys are being played. People with synesthesia related to music may also have perfect pitch because their ability to see/hear colors aids them in identifying notes or keys.[21]

The colors triggered by certain sounds, and any other synesthetic visual experiences, are referred to as photisms.

According to Richard Cytowic,[5] chromesthesia is "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and firework shapes that arise, move around, and then fade when the sound ends. Sound often changes the perceived hue, brightness, scintillation, and directional movement. Some individuals see music on a "screen" in front of their faces. For Deni Simon, music produces waving lines "like oscilloscope configurations – lines moving in color, often metallic with height, width and, most importantly, depth. My favorite music has lines that extend horizontally beyond the 'screen' area."

Individuals rarely agree on what color a given sound is. B flat might be orange for one person and blue for another. Composers Franz Liszt and Nikolai Rimsky-Korsakov famously disagreed on the colors of music keys.

Spatial sequence synesthesia

Those with spatial sequence synesthesia (SSS) tend to see numerical sequences as points in space. For instance, the number 1 might be farther away and the number 2 might be closer. People with SSS may have superior memories; in one study, they were able to recall past events and memories far better and in far greater detail than those without the condition. They also see months or dates in the space around them. Some people see time like a clock above and around them.[unreliable medical source?][22][23]

Number form

Main article: Number form

A number form from one of Francis Galton's subjects (1881).[10] Note how the first 12 digits correspond to a clock face.

A number form is a mental map of numbers that automatically and involuntarily appears whenever someone who experiences number-forms synesthesia thinks of numbers. Number forms were first documented and named in 1881 by Francis Galton in "The Visions of Sane Persons".[24]

Auditory-tactile synesthesia

In auditory-tactile synesthesia, certain sounds can induce sensations in parts of the body. For example, someone with auditory-tactile synesthesia may experience that hearing a specific word feels like touch in one specific part of the body or may experience that certain sounds can create a sensation in the skin without being touched. It is one of the least common forms of synesthesia.[25]

See Part 2 >