The mention of colored hearing dates back to ancient Greek times, when philosophers questioned whether the color of music was a quantifiable quality.
Centuries later, Isaac Newton also claimed that musical tones shared a common frequency with color tones.
In the year 1871, Gustav Fechner carried out the first empirical survey of those with 'colored hearing.' To follow in 1880, was a paper
published by Francis Galton, cousin of Charles Darwin. Interest in synesthesia was lost in the shift to behaviorism, but interest has since been revitalized since the cognitive revolution in the 1980s. Since then, research has focused on the reality, consistency, and frequency of synesthetic experiences.
While the cause of synesthesia has yet to be determined, researchers have developed several theories attempting to explain these atypical perceptual experiences. One of the most adopted theories is the Cross Activation Theory, which states synesthetic experiences are the result of increased connectivity between areas of the brain that are not usually connected. Researchers believe this is attributed to reduced neuronal connection pruning in childhood.
Testing for Synesthesia
Since no direct cause has been determined, it has been difficult to test an individual for this condition. The simplest method of testing is through objective verification. By utilizing a test-retest model, researchers are able to retrieve reliable results from surveys. In testing someone over a long period of time, researchers are able to determine whether they are a synesthete or not. To further understand a synesthetic brain, researchers administer numerous measures that test target areas of the brain believed to be involved in synesthesia.
Synesthesia ResearchR
KIKI/BOUBA Test
This experiment developed by Wolfgang Kohler is a measure of the relationship between speech sounds and visual objects.
In the test, participants are asked to guess which one of the shapes to the left are named "bouba" and which is named "kiki." Astoundingly, 95% of respondants answered that the shape on the left was "kiki" and the one on the right was "bouba." These results suggest that the brain is somehow able to extract abstract properties from the shapes and sounds.
Number Search
Researchers utilize tests like this number search to measure the automacity of synesthetes. Participants are asked to identify the hidden shape in the image on the left. To typical people, the task may prove more difficult than to synesthetes who may excel due to their altered coding.
The image on the right represents a synesthetes perspective, where 2 is associated with the color red, and 5 the color green. This would give a participant an edge in completing the task.
MRI and Brain Imaging
By using the latest brain imaging techniques, researchers are able to determine which parts of the brain are activated during synesthetic experiences.
These methods have provided insight as to which areas of the brain are cross-wired in a synesthetic brain.