The Many Types Of Synesthesia Explained

By Nicola Kirkpatrick

Updated December 19, 2018

Reviewer Aaron Horn

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What's it like to "taste" words or "see" music? If you know, then you might just have the sensory condition known as synesthesia. While there are many types of synesthesia, it is generally described as a phenomenon in which a person experiences a sensory stimulus, such as hearing a piece of music, and another of their senses simultaneously perceives the stimulus. For example, the music heard could trigger the perception of an orange-colored haze.

Evidence of synesthesia has been documented for centuries, but the condition has previously received little attention from the scientific community and the public-at-large. The American Synesthesia Association points out that current "serious scientific attention" to synesthesia and heightened public awareness of the condition may be attributed to widespread internet use and new developments in the use of functional magnetic resonance imaging (fMRI) for detecting brain activity. Both have contributed to the recognition, study and detailing of several types of synesthesia.

How Do the Synesthesia Types Differ?

Someone with synesthesia is known as a synesthete, and there are over 80 combinations of ways in which a synesthete's senses may be linked. For instance, some synesthetes perceive words as a taste, while others may associate different personality traits with each of the 26 letters of the alphabet. Furthermore, while synesthesia is most commonly seen as a link between two senses, there are types of synesthesia in which three or more of the senses are involved. There has also been at least one case in which a synesthete displayed a connection among all five senses.

Another distinction among synesthetes is that their synesthesia can be bracketed into two major groups. Firstly, there is projective synesthesia in which the synesthete hears, sees, feels, smells or tastes the second sensation which is triggered by the initial stimulus. An example of this is a synesthete smelling apples whenever they hear a guitar playing a certain note. The smell of the apples is as real for the synesthete as the sound they are hearing.

The second major category is associative synesthesia. Synesthetes who fall in this group feel the connection between a stimulus and a sense by which it is not normally perceived. In the above example, while a synesthete with associative synesthesia will not smell apples, they will feel a strong association between guitar's music and the smell of apples. There is, of course, some gray area between these two types of synesthesia, as there are synesthetes who describe their experiences in both a projected and associative manner, with the forms occurring both independently and in a mixed or concurrent fashion.

It must be explicitly pointed out that synesthesia is not a reaction which happens selectively or can be typically be "switched off - the synesthete cannot choose when to be synesthetic. Neither is simply a "swapping" of senses or the replacement of one sense with the next. Plus, in the types of synesthesia involving projected colors, those colors do not interfere with colors in the environment. Rather, both are perceived as separate and distinct.

For example, someone who perceives individual numerals as colors still sees the numerals in whatever color they are shown. But, they also, ON EVERY OCCASION, will experience either a very strong association of the numeral to a particular color or they will very clearly see that color projected in some region in space, such as the associated color glowing around the numeral.

It must also be emphasized that while many of the examples given in this article will include the five basic senses, there are types of synesthesia in which the secondary perception is in the form of inner feelings or emotions. Some synesthetes, for example, perceive numbers and letters with personality traits - such as the numeral 5 being optimistic or the letter C being generous.(We will explore these forms of synesthesia in greater detail in the next section of this article.)

There are other distinctions which can be made among the types of synesthesia. These include research findings supporting the theory that synesthesia is more prevalent among women than men, although there are other bodies of research which indicate there is no distinction of synesthesia prevalence between the sexes. For those who maintain that females are more likely to be synesthetic, they generally conclude that the degree of prevalence is much less than previously thought.

Some studies have shown that synesthesia has a genetic link and runs in families. In fact, over 40% of synesthetes have a parent, sibling or offspring who is also a synesthete. Hence, there are some families with multiple cases of synesthesia. A distinction arises, however, where recent research shows that apart from congenital synesthesia, there are some types of synesthesia which can be either chemically induced by psychoactive stimulants or developed through experiences, whether learned or following a traumatic experience. An example of the latter is the link shown between post-traumatic stress disorder (PTSD) and Grapheme-color Synesthesia.

A Close Look at The Most Common Types of Synesthesia

Research and understanding of synesthesia are currently quite fluid, with new findings being regularly reported. The scientific community has, however, established somewhat consistent descriptions of the most common ways in which the various types of synesthesia manifested. Let us delve deeper into some of them.

Grapheme-Color Synesthesia

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Of all the types of synesthesia which have been identified so far, Grapheme-color synesthesia is one of the most prevalent and most studied. In it, the synesthete has a natural association of written letters and numerals to colors. There are some minor similarities among grapheme-color synesthetes regarding which color is perceived about a unique numeral or letter. It is highly unlikely, however, that two persons with this form of synesthesia have very many of the same associations.

The term "cross-wiring" is often used in explaining each of the types of synesthesia about how the brain works. Cross-wiring in the case of grapheme-color synesthesia is thought to occur between the brain's color center and number area, both of which are located in the same region of the brain known as the fusiform gyrus. Some studies have revealed that persons with grapheme-color synesthesia have an increased amount of grey matter in certain areas of their brains, including the fusiform gyrus.

Some persons find it is very advantageous to have grapheme-color synesthesia as it has been proven to aid memory and, by extension, learning. Several studies have focused on this aspect of grapheme-color synesthesia, regarding it as a useful mnemonic device for synesthetes. Other studies have taken this one step further by suggesting that the grapheme-color synesthesia was itself developed in the early childhood stage of a synesthete's life as a learning strategy.

Ordinal Linguistic Personification

In ordinal linguistic personification, the synesthete perceives ordered sequences such as numbers, letters, days, months, etc. as having inherently distinct personality traits and gender. As with many other types of synesthesia, the associations are roughly constant for the synesthete but are not necessarily the same among synesthetes who exhibit the condition. While ordinal linguistic personification has been noted to co-occur with other forms of synesthesia, it has been shown to co-occur with greater frequency in synesthetes who display grapheme-color synesthesia.

As an example of ordinal linguistic personification, the synesthete might feel that the letter A is female, the letter T is male, and the letter M has no gender. They may also perceive the numeral 5 as sneaky and the numeral 9 as fussy. There are occasions, too, in which the letters, numbers, etc. have personal relationships with each other. For example, B and R are friends, and neither one can stand Y. There is also the tendency among synesthetes with ordinal linguistic personification to attribute a trait to an entire word based on the trait associated with the word's initial letter.For instance, if N is a quiet, introspective letter, then the word "NECK" is a quiet, introspective word. It is also worth noting that a synesthete may assign personality traits and gender to objects, as well.

Chromesthesia

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This type of synesthesia is also known as sound-to-color synesthesia and can simply be thought of as seeing sounds. In chromesthesia, sounds heard by the synesthete are associated or perceived as particular colors. The synesthete hears the sound just as everyone else does. In every instance in which the sound is heard, however, they simultaneously and naturally experience a color which remains more or less constant with that specific sound. The perception of the color does not detract from the how the synesthete hears the sound, and in most cases, it is more likely to enhance their overall experience of it. Some chromesthesia synesthetes take advantage of their condition by using sounds (such as playing a piece of music) as a way to help them to relax.

Similar to the pairs found in other types of synesthesia, the pairings in chromesthesia are consistent for each synesthete but are not automatically the same for another synesthete with chromesthesia. What researchers have discovered, however, is that synesthetes tend to associate high pitched sounds with light, bright colors. Low pitched sounds, on the other hand, are more likely to be matched to darker colors. There is also some evidence to suggest this phenomenon can be found (to a lesser extent) among non-synesthetes.

Subgroups among chromesthesia synesthetes include those for whom the condition is triggered by all types of sounds and those for whom musical notes only generate their sound-to-color associations. Furthermore, some chromesthesia synesthetes report that the colors are only evoked by people's voices.A note-worthy group related to chromesthesia synesthetes are persons for whom the condition is color-to-sound, that is, it is colors which are perceived as sounds. In instances where an individual is identified as having both sound-to-color and color to sound synesthesia, it often found that the pairings remain the same in both directions.

Spatial Sequence Synesthesia

Spatial sequence synesthesia is sometimes referred to as visio-spatial synesthesia and is one of the most intriguing types of synesthesia.In it, sequences such as numbers, letters, months and dates are perceived as occupying points in space. A synesthete who experiences this phenomenon may see the spatial arrangement in their "mind's eye" or in the actual space around them.

For example, there are synesthetes with spatial sequence synesthesia who, when thinking of letters, might see A farther away than B and perhaps B higher than C. The arrangement can take different shapes - columns, spirals or circles, for instance. As another example, spatial sequence synesthetes might perceive the time on a clock as located in the specific points in the space around them. So, 12 o'clock has a set location, as does 1 o'clock, 2 o'clock, etc.They can turn toward each time's location, to focus on it and to move toward it.

Interestingly, studies have linked the time-space nature of spatial sequence synesthesia with improved memory, in general, and superior ability to recall events, in particular. Many sources like this type of synesthesia to an ability to see into the past or to travel through time. There have been studies which indicate a very heightened ability among persons with spatial sequence synesthesia to recall the events which have occurred in their own lives. This condition, known as hyperthymesia, is itself linked to autism and savantism.

Mirror-Touch Synesthesia

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This is one of the rare synesthesia types and one of those with the greatest possibility of being an acquired (as opposed to congenital) condition in a synesthete. In mirror-touch synesthesia, the synesthete feels the same sensations as someone else. The mirror-touch sensation can be activated by real-life, in person situations or by watching someone on a screen. Non-synesthetes who enjoy watching particularly violent shows may be horrified to know that a synesthete with mirror-touch synesthesia feels all the pain associated with the maiming taking place on the screen.

Here are a few other examples of mirror-touch synesthesia: While watching a doctor places a cold stethoscope on her child's back, a mother feels the sensation on her own back. Or, while watching a friend rub a sore spot on his shoulder, the synesthete feels that exact rubbing sensation on her shoulder. Or, perhaps while sitting beside someone on the bus who begins to grind her teeth, the synesthete feels the same uncomfortable sensation in her mouth.

Understandably, some studies of mirror-touch synesthesia have linked it to synesthetes having a heightened sense of empathy for the pain being suffered by others. The condition has proven to be helpful to synesthetes with certain professions, such as doctors and massage therapists.

Auditory-Tactile Synesthesia

Auditory-tactile synesthesia (a.k.a. hearing-touch synesthesia) is one of the rarest of all types of synesthesia. It occurred when sounds heard by the synesthete produces a tactile sensation on certain areas inside and outside of the body. Indications are that cross-wiring of the auditory and somatosensory cortices accounts for the experience of auditory-tactile synesthesia.

There are a plethora of sensations which can be experienced and which vary from one synesthete to the next. A sound might feel like a tingling sensation to one synesthete while to another that same sound is perceived as the pressure we normally associate with something pressing against our skin. Sounds have been reported as feeling warm or cold; like you are being tickled; gently brushed by a feather; or like electric shocks.

There are occasions when synesthetes describe the perceived tactile sensation as pleasant but on other occasions, sounds can produce sensations which are distracting, uncomfortable or outright painful - there are synesthetes who report sounds feeling like stings to their skin. The primary stimulus which produces a particular sensation differs among synesthetes with auditory-tactile synesthesia. For some, it may be music which primarily produces the sensations while for others, it may be the sound of the human voice.

Number Form Synesthesia

This, again, is one of the rare synesthesia types and, as such, it has not received as much attention from research as some of the other, more common types of synesthesia. In number form synesthesia, the synesthete involuntarily sees a mental map of any group of numbers they think about. Research into number form synesthesia suggests that the cross-wiring which occurs in the synesthete's brain takes place between close-lying regions within the parietal lobe which governs spatial and numerical cognition.

The arrangements in number form synesthesia differ from the conventional number line we are all taught in school,and they may be idiosyncratic (unique to the individual synesthete), and unchanged throughout the synesthete's lifetime. The synesthete may have a particular form for months of the year and another for dates. Also, the number of forms which are perceived are not related to colors and do not necessarily possess any form of symmetry. The number forms may be complex or simple and may involve curved or straight lines or a combination of both.

Research has suggested that synesthetes are better able to process numerical information if it is presented in a manner which matches their number form for that type of information. This has some implications for how well a synesthete can learn subjects, such as Mathematics, taught conventionally.

Lexical-Gustatory (And Sound-Gustatory) Synesthesia

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This is yet another of the rare forms of synesthesia. A person who has lexical-gustatory synesthesia senses words (both spoken and written) as distinct tastes, smells and textures in the mouth or senses the tastes in their head. The phenomenon has been shown to include non-lexical sounds, that sounds not related to words (such as music or the sound of a jackhammer). Hence the distinction is sometimes made of sound-gustatory synesthesia.

As is the case with some other types of synesthesia, there is evidence to suggest that lexical-gustatory and sound-gustatory synesthesia are developed in childhood rather than being present from birth. Some synesthetes with lexical-gustatory synesthesia tend to make linkages between word and foods they were exposed to as children. In one particular case, the synesthete who spoke both English and French from childhood had taste sensations for words in both languages. Although she also spoke Spanish (but learned it later in her childhood years than the other two languages), she had no experiences of her synesthesia in that language.

The experience of the evoked sensations is often linked to the sound of the word, but some researchers think it may be connected to the meaning of the word, as well. Also, not all words (whether visualized or heard) and sounds induced the same intensity or complexity of taste in the synesthete. Furthermore, they are some words and sounds which produce no taste response at all.

Misophonia

This is one of the rarest of the rare types of synesthesia. In fact, it has only recently begun to be the subject of scientific research and has also only recently begun to receive acceptance as a form of synesthesia. Apart from being one of the rarest, misophonia is also one of the most troubling examples of synesthesia. It is a condition in which the synesthete experiences negative and aggressive emotional reactions to sound. It has been described as a hatred of sound with the most common triggers being human-related sounds, such as breathing, chewing and lip-licking.

Importantly, the sounds which trigger misophonia tend to be everyday, unavoidable sounds. It should, therefore, be easy for a non-synesthete (or a synesthete who does not have this particular form of synesthesia) to understand how misophonia can adversely impact the normal functioning of the synesthete afflicted by it. Approaches used to help synesthetes with misophonia include cognitive behavioral therapy and the inclusion of background noise to mask the annoying sounds.

As we have seen, it is not just the types of synesthesia which are widely different, but also how the condition affects the lives of synesthetes. It is true that synesthesia forms are considered helpful (such as grapheme-color synesthesia aiding memory). On the other hand, there may be cases in which synesthesia proves to be problematic for the person experiencing it (as with misophonia). In these instances, it is advisable to seek professional help. While it may not be possible to eliminate the condition, coping strategies can be learned.

It is also wise to reach out to a mental health professional if you suspect you may any of the synesthesia types described above or have had similar experiences. It could give you the chance to explore your unique situation fully. Who knows - your case may be an as yet unidentified type of synesthesia worthy of further investigation.


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