In the psychological phenomenon known as 'synesthesia', individuals sensory systems are a bit more intertwined than usual.
Some people, for example, report seeing colors when musical notes are played.
One of the most common forms is grapheme-color synesthesia, in which letters or numbers (collectively called graphemes) are highlighted with particular colors. Although synesthesia has been well documented, it is unknown whether these experiences, reported as vivid and realistic, are actually being perceived or if they are a byproduct of some other psychological mechanism such as memory.
New research published in the June issue of Psychological Science, a journal of the Association for Psychological Science, sheds some light on the veracity of these perceptions.
Danko Nikolic, a researcher from the Max Planck Institute for Brain Research in Frankfurt, Germany, and his colleagues relied on a variation of a classic psychological method known as the Stroop task to test this. In this task, participants must name the color of the font that a color word is printed in. For example, if the word blue was printed in red ink, the participant would say red a moderately difficult task that requires some mental gymnastics.
To understand Nikolic's version of the experiment, a rudimentary understanding of color perception is required: When anyone views a particular color, specific neurons in the visual cortex area of our brain are activated. These specific neurons will deactivate, however, if a color from the opposite end of the spectrum is presented. So, any neuron activated when the color blue is present will deactivate when it's exact opposite, yellow, comes into the visual field.