Number-form synesthesia

Also occasionally called number-space synesthesia

A type of spatial sequence synesthesia

(Image: Ailsa in Ailsa Brims Fine Art)

People with this type of synesthesia perceive numbers as a sequence visualised spatially, around them or in front of them. The spatial positioning is highly consistent and tends not to vary throughout the synesthete’s lifetime. For many of these people, each number also has its own colour (so number-form coexists with grapheme-colour synesthesia in this case), or their number maps have shading effects. These synesthetes frequently visualise the numbers spatially in relation to themselves, with a perspective that varies according to the number they have in mind at any given time. The maps are three-dimensional and assume many different forms: they can be straight or curving, with one or more changes of direction, with right angles, peaks and dips, spirals, zigzags, steps or ladder-like structures, going from right to left or vice versa, climbing up or disappearing on the horizon as the numbers get larger, and they may look tidy and well-organised or appear chaotic, only making sense to their “owner”. In any case, it can safely be said that there are as many spatial numerical maps as there are number-form synesthetes, as this type of synesthesia is just as idiosyncratic as any other.

(Image: Sarah, in the blog Terra Nomad.)

Prevalence of number-form synesthesia

What percentage of synesthetes have this specific subtype? There do not appear to be any studies giving a conclusive number, but it probably occurs in the majority of people who have calendar synesthesia (estimated at 20%, N. Sagiv et al, 2005) and also in some others who do not have the calendar type, so it is likely to be relatively common.

It is certainly possible for non-synesthetes to have automatic, consistent and idiosyncratic visual number maps, and many people, if asked, would be able to describe how they visualise numbers in their mind, and they are not always just in a straight line. There is therefore some overlap between the synesthetic and the non-synesthetic in the case of this phenomenon, although it has traditionally always been considered a type of synesthesia. In his book The Hidden Sense, Chretien von Campen says:

"You don’t have to be a synesthete to be able to perceive number forms and time forms. Some nonsynesthetes also perceive them. Rosanne van Klaveren does not perceive numbers in colors but has clear spatial representations of number forms.  (...)

Now we know that many people, about one in ten, use these number forms in arithmetic—sometimes without being very aware that they are doing so.

You can figure out whether you are using number forms by trying to imagine a visual depiction of, for instance, the numbers 0 to 100. If you can draw it on paper you probably have a number form."

The difference between synesthetic and non-synesthetic number form visualisation is that synesthetes are likely to have a more vivid visual map that seems ever-present and which they summon up with no effort whatsoever whenever they think of numbers or need to use them, a map that seems so spatially "real" to them that they feel able to move around inside the space where it exists or manipulate it mentally, bringing parts of it closer to them to get a more detailed view of the numbers. It is also typical of synesthetes that the numbers are coloured, as it tends to coexist with grapheme-colour synesthesia. If a person has a number map that is not strongly or automatically present and they do not have any other types of synesthesia, then it is unlikely that they meet the criteria to be considered a synesthete.

Association and projection

The vast majority of number-form synesthetes visualise their number map in their mind's eye and do not see it phyiscally around them as if it was really there, even though its position in space is totally clear, it is vividly materialised in their mind and it is wholly consistent, with the numbers never changing place. There may be a small percentage of true projector synesthetes with number-form, who actually see the photisms appear around them as if they were projected on a screen in real life.

(Image: from the book Des Phénomènes de Synopsie by Théodore Flournoy, 1893, p163.)

This 55-second video offers us a realistic 3D animated vision of how its author, The Stellar Jay, perceives their number line. It includes twists and turns, varying speeds, perspectives and spatial distancing and it goes from zero up to several thousands:   

(Source: The Stellar Jay YouTube channel. Video posted here on the Synesthesia subReddit. 2026.)

Having this type of synesthesia often helps the synesthete to perform mental calculations and these people sometimes excel at mathematics, as they can easily navigate through their visual numbers, handling and remembering them at will.

Here are two more representations of number-form synesthesia. The first is from a scientific study documented almost 150 years ago:

(Image: Francis Galton, 1881)

The second is an exquisite depiction of how numbers can surround the subject in three-dimensional space, created by synesthete psychologist Maike Preissing, host of the Let's Talk Synaesthesia podcast:

Not just numbers: mental maps for other measurable sequences 

All the above examples are for ordered natural numbers, but some synesthetes also have mental maps for other quantative sequences: age, height and/or weight measurements, temperatures (meteorological or body temperature), clothes sizes, shoe sizes, salaries and so on.

(Images: Weight in lbs and people’s ages, by Rebecca Schulz Kluchnyk, posted to the Facebook group Synesthesia. 2020.)

Here are some related types of synesthesia you might be interested in reading about:

Alphabet-form synesthesia

Spatial sequence synesthesia in general

Calendar synesthesia

More cases / readers' comments: read all the comments on this article here

(See the latest comments received below, or follow the above link for access to all the reader comments describing their own experiences: it makes interesting reading)

This page last updated: 27 May 2026