What is Synesthesia? - Definition & Examples

Instructor: David White
Synesthesia is a type of crossing of the sensory wiring that can cause some fascinating (and occasionally alarming) results. Through this lesson, you will learn the definition of this phenomenon and explore some examples and indicators that can help with a diagnosis.

Defining Synesthesia

Like many teenagers, the year that I got my driver's license I spent countless hours driving around aimlessly with friends and listening to music. It's been many years since then, but every now and then I'll hear a song from that year and suddenly begin to smell a faint coconut scent in the air. I eventually recognized this smell as the air freshener from my car the year I obtained my license. For quite some time I was alarmed by this, until I learned that what I was experiencing is a fairly common phenomenon known as synesthesia.

Synesthesia is a neurological phenomenon that causes one sensory response to automatically trigger another sense simultaneously. In general, very little is known about synesthesia or precisely why it occurs. Moreover, it can be difficult to identify because it might only happen to a person under certain circumstances and they might not pay much attention to it.

Synesthesia is a crossing of sensory wiring that causes two or more senses to respond to one stimuli.

Researchers are divided on what causes synesthesia, but most agree that it is not a symptom of any illness and occurs in people with average or above average intelligence. The predominant theory holds that at some point during a person's neurological development, the synapses that are contained within each sensory system get crossed and cause these experiences.

Diagnosing Synesthesia

While there are no clear diagnostic criteria, there are certain things that doctors look for in determining whether or not a person is experiencing synesthesia. The most significant of these is that the experience must be involuntary rather than the result of using your imagination. Similarly, the perception will be the same every single time. In my example about the music that I associate with the scent of coconut, it's actually one particular song and it happens every time I hear it.

Another important criterion is that the perception is a projection, which means that it occurs outside of your imagination. This criterion might be a little confusing, but consider that as you read this you're probably picturing in your head what this would be like - imagining letters that cause tastes or different colors or sounds that are accompanied by smells. In the case of synesthesia, the person isn't just picturing it in their head, they are actually seeing, hearing, or smelling it as though it were right in front of them.


The most common reference to synesthesia is color synesthesia, which is a condition that causes a person to associate letters or numbers with particular colors. When the person writes down someone's phone number, for example, they might see each number written in a different color. In cases of color synesthesia, the numbers or letters always have a corresponding color that should remain the same every time. This means that if they see the number 5 as blue, they should always see the number 5 as blue.

Color synesthesia causes a person to associate a concept with a color.

It is important to note that although color synesthesia is often referenced in discussions of the phenomenon, it's not actually synesthesia. If you'll recall, synesthesia is a neurological response in which two or more senses are activated in cases where only one should be activated. In experiences of color synesthesia, there is only one sense being activated (sight) as the letters or numbers are associated with a color. Given that, this experience is often referred to as ideasthesia because it involves a sense and a concept coming together rather than two senses.

Researchers tend to be divided on what is and what isn't synesthesia. For some, color synesthesia might be considered synesthesia, while for others it might be ideasthesia. The latter of the two is really a technical differentiator, so for a person to refer to color synesthesia as simply synesthesia isn't entirely incorrect.

Synesthesia and Memory

Setting aside the technical hair-splitting between synesthesia and ideasthesia, both have an incredible influence on the ability to remember. In general, the more a person is able to associate a fact or memory with other things, like people or dates, the more likely they are to retain the memory. Therefore, synesthetic perceptions are able to be recalled with greater ease and clarity.

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