Synesthesia literally means “joined perception” (“syn” together & “aesthesis” perception) and is a blending of two or more senses simultaneously perceived into one anomalous event – a cross-wiring between brain areas that are normally segregated in nonsynesthetic individuals.

For example, synesthetes may hear, smell, taste or feel pain in color. Others taste sounds or perceive letters and numbers in color. And the perception is the same every time for an individual, although they may differ from person to person.

The most common type of synesthesia is called grapheme-color synesthesia and involves seeing monochromatic letters, digits and words in unique colors.


An example of how nonsynesthetic (left) and synesthetic (right) individuals might see a set of numbers.

The neural mechanism causing synesthesia remains unknown but it seems to be a dominant trait and it may be located on the X-chromosome (supported by the fact that synesthesia appears often inherited). Some developmental scientists speculate that all humans are born synesthetic but that normal developmental results in more segregated perception areas of the brain, and still synesthesia is not considered a neurological disorder.

The occurrence of synesthesia is in question, with some estimates being one in 2,000 and others being as low as one in 200. Women are more likely (as much as three to eight times) than men to have synesthesia, and synesthetes are more likely to be left-handed.

Some Characteristics
Synesthesia is more common among artists, musicians, and novelists (8 times more likely) and some very famous people are known synesthetes including: Vincent Van Gogh, Marilyn Monroe, Leonard Bernstein, Duke Ellington, Itzhak Perlman, Stevie Wonder, Billy Joel, and Lady Gaga.

Franz Liszt was quoted as telling his orchestra instructions such as,

“O please, gentlemen, a little bluer, if you please! This tone type requires it!” or, “That is a deep violet, please, depend on it! Not so rose!”

And some synesthetes like the physicist Richard Feynman possess “conceptual synesthesia” where they see abstract concepts: units of time, mathematical operations, shapes. Feynman once said,

“When I see equations, I see the letters in colors – I don’t know why. As I’m talking, I see vague pictures of Bessel functions from Jahnke and Emde’s book, with light-tan j’s, slightly violet-bluish n’s, and dark brown x’s flying around.”

One interesting characteristics of synesthesia is that it seems to enhance memory – the secondary synesthetic perception is remembered better than the primary perception

And one perplexing characteristic is the typical experience of seeing characters in two colors at the same time: the original printed color and the synesthetic color.

Synesthesia as human experience
Neuroscientist Vilayanur Ramachandran gave an excellent TED Talk where he discussed three examples of connection between cerebral tissue in the brain, one of which was synesthesia. In the talk Ramachandran made the case that the type of cross-wiring which occurs in synesthesia actually happens with us all, but we don’t recognize it. One example would be the way we experience sound coupling in movies, with images and spoken words coming together as one experience. Ramachandran provided a simple example. He called the characters below letters of a Martian alphabet and named them “booba” and “kiki.” Then he asked his audience to guess which was which – they almost unanimously said that booba was the image with rounded shapes and kiki was the one with jagged shapes.


We are all somewhat synetheisc.

Web applications
I see an interesting potential for usability that might come from better understanding synesthesia – better consumption of visual and textual information. One simple example can be found in the Beeline Reader, an application that converts text into color gradient text to make it more readable.

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Saccadic eye movements

A saccade (sakad′ik – French, twitch, jerk) is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. Saccadic eye movements are extremely fast voluntary movements of the eyes, allowing them to accurately “refix” on an object in the visual field, and change retinal foci from one point to another. Some Saccadic eye movements can be involuntary.

Saccades are one of the fastest movements produced by the human body with peak angular speeds of the up to 900°/s. An unexpected stimulus can commence a saccade in about 200 milliseconds (ms), and last from about 20–200 ms, depending on their amplitude. 20–30 ms is typical movement for language reading.

We do not look at the world with fixed steadiness, although our brain tells us otherwise. Our eyes move around, locating interesting parts of the scene and building a mental map in three-dimensions. Our eyes saccade, or jerk/twitch quickly, stop, scan, and then move again. The fovea (the high-resolution portion of vision, 1-2 degrees of vision) is one of the main reasons for Saccadic eye movements – we must move our eyes to resolve objects in our minds.

Saccadic masking
One of the most interesting points about Saccadic eye movements involves what we don’t perceive as our eyes move. One would think that no information is passed through the optic nerve to the brain while the eyes move in saccade, that is at least our perception experience, but that’s not correct. Saccadic masking or saccadic suppression begins just before your eyes move and keeps us from experience a blurred or smeared image. You can experience the saccadic masking effect with a very simple experiment: look in a mirror, look at your left eye, then change your gaze to look at your right eye – you won’t perceive any movement of your eyes, which is evidence that the optic nerve has momentarily ceased transmitting or that the brain just refuses to process the transmission.

Spatial updating and Trans-saccadic perception
One of the continually amazing things about perception is that our brain often perceives information that isn’t there. Spatial updating occurs when you see an object just before a saccade, and allows you to “make another saccade back to that image, even if it is no longer visible.” The brain somehow “takes into account the intervening eye movement by temporarily recording a copy of the command for the eye movement” and compares it to the remembered target image.

Trans-saccadic memory is the process of retaining information across a saccade. Neurologist think that perceptual memory is updated during saccades so information gathered across fixations can be compared and produced, creating what researches believe is a type of visual working memory.

Saccadic Dysfunction
There are a series of disorders that can produce abnormal eye movements. One is Nystagmus (also known as “dancing eyes”) a condition of involuntary eye movement (side to side, up and down, and other) that may reduce or limit vision.

Web Development Application
The understanding of saccadic eye movements has had a remarkable impact on Web usability in the form of eye tracking studies. By employing technology that monitors eye movements that can pinpoint precisely where a user is looking on a page, usability testers can study and better understand how people interact with text or online documents.

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What reality are you creating for yourself?

There’s a story from the mid-20th century of an anthropologist studying pygmies in a jungle of Africa. He took one pygmy on a trip to the savanna. The pygmy had never been out of his jungle. He saw a herd of willdabeast in the distance and asked the anthropologist what type of insects they were – he had no practical frame of experience for understanding such distances. Our cultural or life experience can frame perception . A person who grows up in the plains will judge distances better but will misjudge the height of buildings and trees when compared to someone who grew up in woodlands.

What we perceive is a construct, in a very real sense, our minds create reality. For example, perspective is a illusion that we all accept on some level, even though we know that objects in the distance are not smaller (see blog cover photo).

Isaac Lidsky’s Ted Talk looks at how important vision is to us, how it constructs our sense of reality, an in his case, how it can be a sort of trap if you let it. His journey is about losing his site, and coming to the realization that he summed up in a statement by Helen Keller, “the only thing worse than being blind is having sight but no vision.”

Some interesting points from the talk about perception:

  • Hearing requires 2 – 3% of the brain’s processing capacity
  • Touch uses approximately 8%  of the brain’s capacity
  • The visual cortex takes up about 30 % of the brain’s capacity and processes as many as two billion pieces of information each second

But Lidsky explains that all information references “your conceptual understanding of the world” based on the context of your life, “knowledge, your memories, opinions, emotions,” etc. One example he gives …

“… what you see impacts how you feel, and the way you feel can literally change what you see … a hill appears steeper if you’ve just exercised, and a landmark appears farther away if you’re wearing a heavy backpack.”

Crash Course provides another overview of how perception comes together in the brain in Perceiving is Believing

Web Development Application
No direct application but it is helpful to know how demanding the visual cortex is. It also may be helpful to think about cultural (or emotional) frame of references when developing images and content for a Web page.

Related TEDTalk: Isaac Lidsky TED Talk

Post Script

TEDTalk by Anil Seth, "Your brain hallucinates your conscious reality"
According to neuroscientist Anil Seth, we're all hallucinating all the time; when we agree about our hallucinations, we call it "reality."

One interesting point of the Ted Talk is a section on introception – stimuli produced within an organism, especially in the gut and other internal organs.
Anil Seth TED Talk