When:

• Black printed letters or numbers have colour, or a personality, or
• music is seen in color, or
• days, weeeks or months of the year appear in shapes like squares, circles and ovals, or
• sounds or words have a taste, or
• tastes have shapes, or
• faces have an aura, or
• sounds have smells or temperature

then synesthesia appears to be involved. (in fact about half the people experiencing synesthesia have more than one form of it)

Types of Synesthesia

Most defintions of synesthesia refer to cross modal sensory experiences. That is experiences where a percept in one sense initiates or co-occurs with a percept in another sense. This in itself is not uncommon. Scientists are starting to learn that the brain integrates sensory information all the time. Perhpas the way we see synesthesia will change over time as we understand it more and people discuss it more readily. Some artists and musicians would argue that we all have some synesthesia (ability to join the senses) but that some people do it more readily and more permanently than others. Here are some types of synesthesia that have been reported.

One example of this is when you listen to music and you see visual images like colours or shapes. This form of coloured hearing is called Chromesthesia.

There are however a number of synesthesia types where the percept initiates another class of percept in the same sense. One example of this is when you see black printed letters or numbers as having a color associated with them. This is referred to as grapheme / number to color  synesthesia. We are going to look at a few of the different types below.

The most common form of synesthesia (at least the one most widely studied) is grapheme / number to color. Graphemes (letters of the alphabet) or numbers visually presented in black typeface can initiate the experience of colour. The synesthetes who experience this often report that the color is superimposed on the letter in the external environment but many also report seeing the colour in the minds eye.  Exactly how these reports are different is dificult to determine from a scientific and research point of view, but one thing seems likely – these experiences are perceptually real and not imagined. That is, the synesthetes color experience may utilise similar pathways in the brain as normal color vision.

There are a number of other types of synestheisa as well. Ordinal Personification for example. This is where a number elicits a personality. For example 3 is a young boy eating ice cream and 8 is his sister.

‘Time’ to ‘Space’ correlations are also reported. Here time units – like days or weeks  – are spatially linked to form shapes in external space. Each person experiences this differently so the shapes can vary from person to person. One research report (Smilek, et al, 2006) reports a subject who sees May as a blue area located on the right area of her body about an arms length away.