Duality synesthesia or stimulus-dichotomy synesthesia

Some synesthetes involuntarily classify a wide range of concepts and objects as either odd or even. This is called stimulus-parity synesthesia. However, there are other variants of this phenomenon, where the two opposing categories are not odd and even but other concepts. The inducers that trigger this involuntary classification are words, letters, numbers, objects, colours, sounds or types of music, people, animals and even all concepts in general.

Some of the opposing categories that have been observed are:

Masculine or feminine

Positive or negative

Left or right

Up or down

Warm or cold

Light or dark

Wet or dry

Closed space or open space

Round or sharp

Good or bad

Pretty or ugly

Thin or thick

One pallet of colours or another (warm colours or cool colours, for example)

"Duality synesthesia" is the name I suggested for this phenomenon on finding the above cases of it. However, in 2015, the name "stimulus-dichotomy synesthesia" was used to refer to it in this study by Rebekah C. White and Anna Plassart, the researchers who first reported on stimulus-parity synesthesia and coined the term for it. In this paper, entitled "Stimulus-parity synaesthesia versus stimulus-dichotomy synaesthesia: Odd, even or something else?", they also studied a case of a synesthete who labelled concepts as being either negative or positive.

Here are some descriptions written by people with this type of synesthesia:

Warm or cold

“I group words into two categories: warm and cold depending on the feeling I get from them. It's extremely difficult to explain. Like the word "vanilla" is warm, and "chocolate" is cold. Even common words apply. For example: "the", "and", "on", "these" are all warm. "There", "or", "over", "those" are all cold. My sister thinks this way too, but she calls it left and right.”

(Source: This post on Reddit/Synesthesia. 2020.)

Two opposing colour palettes

“I see numerous dichotomous concepts as having either one color palette (red, yellow, pink) or the other (dark blue, green, black).”

(Source: this contribution to the Facebook group Synesthesia World. 2020. The author of the image, Aurore Zelazny, writes an interesting blog called Synesthesia Research.)


  1. Warm thing are even
    Vanilla is warm, so it is even, apple pie is warm so it even. Christmas is warm, it is even.
    Cold things are odd
    Pools, are cold so they are odd. Ice cream is odd unless it has chocolate then it’s even. Ice is cold and blue so it’s off. Blue is cold, so it’s odd. Ocean is deep and scary so it’s cold and black, thus it’s odd.

  2. Language opposites
    Russian and Japanese
    Vietnamese and Filipino