Understanding synesthesia: cross-sensory perception and neurological mechanisms

Synesthesia

What is synesthesia?

Synesthesia means "joined perception" (Phillips, 2010). In the simplest terms, synesthesia refers to a condition in which a person has cross-sensory experiences, such as seeing colors in sounds, tastes, smells, cutaneous experiences, or even numbers or letters of the alphabet (Birren, 1961). In more complex terms, it has been described as the condition in which " a stimulus elicits an image in a sensory mode other than the one in which the initiating stimulus is presented," such as smelling sights, hearing tastes, or touching colors (Roeckelein, 2004). Although the phenomenon was first documented around 1873, Sir Francis Galton is generally credited with its "discovery" ten years later (Roeckelein, 2004). Galton referred to those with the condition as "color-thinkers" (Birren, 1961). In 1955, Simpson and McKellar devised a method for categorizing the different types of synesthesia by using two hyphenated words -- the first for the imagery and the second for the sensation (Roeckelein, 2004). For example, someone with gustatory-visual synesthesia would experience "taste imagery" to accompany the sight of colors (Roeckelein, 2004). Since its discovery, synesthesia has been a popular topic of research, discussion, and speculation in certain scientific circles; today there are entire websites devoted to the subject.

The most common form of synesthesia is known as "colored numbers," referring to the condition in which a person always associates numbers or letters with specific colors (Phillips, 2010). In the rarest of cases, a person may experience three or more senses from an initial stimulus, such as smelling and feeling a color (Phillips, 2010). As would be expected, every case of synesthesia varies in the particular sensory associations that are made; for instance, one may see the number one as red, while another will see it as white (Phillips, 2010).

It's difficult to measure the percentage of people who experience synesthesia since it does not affect other abilities, and many people either don't know they have it, don't know what to call it, or believe that everyone has similar experiences. In addition, everyone has synesthetic experiences to some degree, such as "seeing red" or "feeling blue." Synesthesia is most often found in women, left-handed people, and those with average to above average intelligence (Phillips, 2010). It is also thought to be a dominant trait inherited via the X-chromosome (Phillips, 2010).

How is it diagnosed?

Various tests have been developed to help diagnose synesthesia, and a few can be found online. But one of the leading synesthesia researchers, Dr. Richard Cytowic, has compiled a list of standards that he believes must be met for a diagnosis. These standards describe synesthetic perceptions as: involuntary, projected rather than imagined, constant over time, emotion-provoking, and simple in nature (Phillips, 2010). In addition, people with synesthesia often mix-up the initial perception with the accompanying sensation; for example, a person who sees the color red when hearing the name "Bruce" might better associate Bruce himself with red than with the name Bruce (Phillips, 2010).

Ramifications

The study of synesthesia could shed light on many neurological functions not yet completely understood, such as left-handedness, differences in male and female brains, and the roots of creativity. In fact, many people known to have had synesthesia were highly creative -- composers, poets, or authors. Synesthesia is also being studied for what it may reveal about human consciousness (Phillips, 2010). For example, particularly in light of the recent finding that suggests synesthesia is the result of higher-level processing, researchers may finally be able to solve the mystery of the "binding problem" (Bargary & al, 2009; Phillips, 2010). The "binding problem" refers to how the brain puts together all of its sensory perceptions into one whole experience, such as determining that a dog is a dog (Phillips, 2010). This area of study could also have implications for the burgeoning field of artificial intelligence, which seeks to understand how man can be so superior to machine when it comes to certain types of information processing.

In addition, advertisers are interested in phenomena related to synesthesia, such as how to invoke certain emotional reactions in consumers with specific sights, sounds, etc. (Nelson & Hitchon, 1999). This type of synesthesia, common to everyone, is known as "metaphorical synesthesia" (Nelson & Hitchon, 1999). One 1999 study found that "cross-sensory ads are perceived to be pleasanter and more novel than literal ads," and "cross-sensory ads were preferred over literal ads when subjects were asked to select the better ad" (Nelson & Hitchon, 1999). This makes sense in that the cross-sensory ad should be more stimulating overall, but the psychological implications warrant further research. For instance, what personality types most prefer the synesthetic ad?