What is Synesthesia?
Synesthesia is a medical condition in which the stimulation of one sense results in the additional perception of another sense; for example, perceiving a certain smell every time a specific color is viewed. Estimates on how many people have synesthesia range from 1 in 200 to 1 in 100,000 due to the difficulties associated with testing for it. (Cytowic, 1995) Clinically, there are five requirements for the mixing of senses to be diagnosed as synesthesia (Cytowic, 2004):
It must be involuntary and automatic:
This means that the perception of the outside sense must be instantaneous with the onset of the stimulus, and the subject cannot refrain from experiencing the mixing of the senses.
The perception must be spatially extended:
This condition is a bit more subjective, but it generally means that the synesthete must have the awareness of ‘reaching out’ to perceive the additional sensory input, unlike innate sensations such as vision or smell.
It must be durable and generic:
‘Durable’ simply refers to the lifelong presence of synesthesia within one who experiences it; the perception of mixed senses doesn’t vanish with age. ‘Generic’ means that the sensations are not detailed or extremely specific, but are reduced to general terms such as ‘blobs’ of color, or the feeling of ‘sourness.’
It must be memorable:
Those affected by synesthesia must have measurably high memories, indicating some link between memory and sensory mechanisms in the mixing of senses. This link may take place through the limbic system, which includes structures responsible for memory development as well as structures which relay sensory information throughout the brain.
It must be affect-laden:
Some tasks which would seem trivial to average people affect synesthetes in noticeable ways. Recalling phone numbers, for example, can be extremely enjoyable for synesthetes to experience due to the sensations of colors associated with the recalling of the number. Contrarily, discordant sensations such as mismatched numbers can induce unpleasant emotions, in some cases as strong as intense nausea.
The most common form of synesthesia is the association of specific colors with each letter or numerical digit; this is known as grapheme-color synesthesia (‘grapheme’ simply means letter or number). For example, someone with grapheme-color synesthesia might always perceive the number ‘2’ as being a “red number.” Some people (about 10% of those with grapheme-color synesthesia) perceive the color as being ‘projected’ onto the grapheme (Asher. 2006). For the rest, the perception of color is completely internal; they ‘feel’ or ‘sense’ the color rather than actively ‘see’ it.
It’s important to understand that most people who have synesthesia don’t see it as an affliction. In fact, many of them would look upon the loss of their synesthetic abilities as an advantage. Grapheme-color synesthesia helps with memorization and recall of both numbers and words, due to the unique color coding associated with each word or number. For example, homonyms such as “break” and “brake” evoke very different color sensations within the mind of a synesthete, making it even simpler to distinguish between the two than through the distinction of spelling alone (Cytowic, 2004).
In addition, the process of visual search is greatly quickened in people with synesthesia. To illustrate, take a look at Figure 1:
As you can see, the process of finding the 2’s within the field of 5’s becomes much easier when each digit is associated with a different color. Though the perceived color of the numbers varies between synesthetes, the ability of someone with synesthesia to process visual search fields such as Figure 1 more quickly than the average person remains consistent across all cases.