Autism; a fascination with letters & numbers

As you may know, I’m a graphic designer by profession. Fundamentally, graphic design is about communicating ideas visually; it’s about using shapes, color, images, and text to convey a message, evoke emotion, direct your attention, or prompt action, whether it’s an album cover, a website, an advertisement, signage, or a book. Fascinated with, books and reading from a young age, I later specialized in typography and became a type designer. So not only do I use letters—I design them, too.

In other words, I LOVE letters. And as research from 2024 shows, apparently so do many autistic children! Oh, and numbers. As a type designer, I design those as well.

Optional geek interlude

Skip this section if you want to avoid a deep-dive detour that’s not essential to the core of this article, which is about the findings of the research paper.

The field of type design is interesting, as it seems to attract designers with elevated autistic traits. I’ve said it in jest, but I’m actually quite serious when I say that I suspect that most serious type designers are autistic.

To be a type designer requires a deep and enduring love for letters, a great eye for detail, a deep understanding and adherence to a long list of obscure typographic rules and design principles (e.g., when there is need for optical compensation; how to optimize legibility and strike a balance between legibility, readability, and personality; how to establish a rhythm and when to break the rhythm to maintain legibility and readability, and so forth), and the ability to meticulously design a broad communication system (a typeface, consisting of multiple fonts, each with adequate language support so people can use it to write various languages).

In other words, to be a type designer requires a deep understanding of a rather niche profession (which makes one feel like a lone wolf among graphic designers), a prolonged obsession with letters and typefaces (i.e., typography as a special interest), and a willingness to engage with the many rules that govern typography and mediate reading (the deep engagement with this system of knowledge is a form of hyper-systemizing), and the ability to see a typeface project to its completion. Admittedly, that last one has been difficult for me, as with my ADHD, I take more enjoyment in exploring new ideas for typefaces than working on the same idea for about 100+ hours to complete a full font family. Below are the two master weights of one of my unfinished typefaces, Coalesque.

But from this description, I think you will agree with me that autistic traits lend themselves well to designing typefaces, and that, in all likelihood, it’s people with many autistic traits who tend to gravitate to a profession like this. As such, I wasn’t all that surprised to find research that shows that autistic children show a greater fascination with letters (and numbers) than neurotypicals. That certainly accounts for my life trajectory and affinity for type.

Enhanced interest in letters & numbers

Neuroscientist and autism researcher Alexia Ostrolenk and her team noted that up to 20% of autistic children show hyperlexia, which is an unusually advanced ability to read at a young age, mediated by an intense and precocious interest in written material. Based on this claim (I call it a claim because there is a caveat to the prevalence rate; see the next section on hyperlexia), they explored whether autistic children showed a broader interest in written materials (regardless of hyperlexia).

Here are some of their key findings based on children under the age of 7:^[1]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

• 22–37% of autistic children showed an intense or exclusive interest in letters, compared to 3% of non-autistic ND children
• 17% of autistic children showed an intense or exclusive interest in numbers, compared to 2% of non-autistic ND children
• Autistic children showed this greater interest in letters and/or numbers, even though 76% of them were minimally or non-verbal
• Autistic children often pursue letters and numbers independently, without social cues; whereas neurotypical children showed more interest in letters within a social context
• This early interest may support language skills, even when verbal communication is delayed

Hyperlexia prevalence

Prevalence of hyperlexia in autistic children

Ostrolenk et al. don’t offer a reference for the 20% prevalence of hyperlexia, but based on a systematic review I looked at (which is also by Ostrolenk!), this may be an overestimate; the review noted the following prevalence rates:^[2]Hyperlexia: Systematic review, neurocognitive modelling, and outcome (Ostrolenk et al., 2017)

• Based on the DSM-III definitions of autism and hyperlexia, in 1985 the prevalence of hyperlexia in autistic children was estimated to be 6%^[3]Hyperlexia and a Variant of Hypergraphia (Burd & Kerbeshian, 1985)
• Based on the reading profiles of 130 autistic children and a broader definition of hyperlexia (the discrepancy between word identification/rapid letter naming, and comprehension), in 2014 a prevalence of 9.2% was found^[4]Reading and math achievement profiles and longitudinal growth trajectories of children with an autism spectrum disorder (Wei et al., 2014)
• In 2009, based on less strict criteria for hyperlexia (the discrepancy between reading and IQ at the 10th percentile of the general population), a prevalence of 14.1% was found^[5]Reading and arithmetic in adolescents with autism spectrum disorders: Peaks and dips in attainment (Jones et al., 2009)
• In 2002, based on even broader criteria for hyperlexia (reading/decoding scores two deviations [i.e., 30 points] above measured IQ, and reading/decoding scores at least two years beyond their age), a prevalence of 20.7% was found^[6]A Descriptive Study of Hyperlexia in a Clinically Referred Sample of Children with Developmental Delays (Grigorenko et al., 2002)

Here is a nice diagram Ostrolenk et al. provided:^[7]Hyperlexia: Systematic review, neurocognitive modelling, and outcome (Ostrolenk et al., 2017)

So clearly, the prevalence of hyperlexia among autistic children increases based on how broadly hyperlexia is defined. While I personally don’t see a reason to object to the last definition, I think the claim that 20% of autistic children are hyperlexic deserved more context. Oh and it’s 20.7%, not 20%. Let’s be pedantic about numbers. 🤭

Prevalence of autism in hyperlexic children

Ostrolenk et al. also found that:^[8]Hyperlexia: Systematic review, neurocognitive modelling, and outcome (Ostrolenk et al., 2017)

• In 63.41% of the cases of hyperlexia they looked at, there was either an explicit autism diagnosis or autistic features were explicitly mentioned
• In 84.15% of the cases of hyperlexia, there was evidence of either autism or several autistic features

This confirms a strong association between autism and hyperlexia. Although no prevalence of hyperlexia in the general population was given, there is evidence of hyperlexia being far more common in autistic children.

Onset of fascination with letters & numbers

Okay, so autistic children are much more likely to be hyperlexic. So when do autistic children develop a fascination with letters? And what about numbers? Ostrolenk and her team found that:^[9]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

• The median age at which the interest in letters, written words, and reading develops is 30 months (age 2.5) for autistic children
• Surprisingly, for neurotypical children, it’s actually slightly earlier: 28.5 months.
• The research also identified a third group, which is referred to as the “clinical group,” whose interest in letters and numbers was delayed by 6 months

So who is this clinical group? Well, the study used three different samples:

• Autistic children, meaning children who were assessed for autism and diagnosed with ASD
• A clinical group, consisting of children who were assessed for autism but were not deemed autistic, but who may have received an alternate diagnosis
• TD children, meaning children with typical development, who were recruited from 6 daycare centers, with the requirement that they didn’t have any first-degree relatives with neurodevelopmental conditions

Now, the paper states that a delay of 6 months was noted in the clinical group, but that typically developing children (i.e., neurotypical children) showed no delay in their interest in letters and numbers compared to autistic children. I think it’s a mistake to call this group neurotypical children. Not having relatives with neurodevelopmental conditions is not sufficient to declare a child neurotypical, especially not when one or more of those relatives may be undiagnosed.

Whereas the “clinical group” have been assessed by clinicians, so we can be quite confident they are not autistic. However, they may have received alternate diagnoses. Since they were referred to a clinician for an autism assessment, it’s clear they were showing some autistic traits that warranted the referral. Based on that, I imagine some of these children have ADHD.

So why does this mixed group of neurotypical children and non-autistic neurodivergent children show a delay in interest in letters and numbers? Unfortunately, the paper doesn’t explore that. It’s possible that some of them had developmental delays that were confused with autism. Maybe for some, co-occurring ADHD is associated with a later onset for whatever reason. I wish the paper had accounted for ADHD, but I wish that about most studies on autism. It’s always helpful to account for variables, especially considering ADHD occurs in about 70% of autistic people.^[10]Identifying comorbid ADHD in autism: Attending to the inattentive presentation. Research in Autism Spectrum Disorders (Rau et al., 2020)

For the onset of interest in letters and reading, the three groups converge at 60 months (5 years); the clinical group is showing a flatter curve early on, meaning their interest in letters and reading develops more slowly, and then between 30–40 months, they start catching up a bit with the other two groups; and at around 5 years about 88% of all three groups show an interest in letters and reading.

For numbers and mathematical symbols, the three groups diverge more at 36 months, and only after 72 months (6 years) does the majority of all three groups show an interest.

Prevalence of intense interest in letters & numbers

Assessment reports

According to the assessment reports, 20% of autistic children mentioned an intense or exclusive interest in letters, compared to 3% of the clinical group (non-autistic neurodivergent children). For an intense or exclusive interest in numbers, it was 17% compared to 2%. Unfortunately there are no assessment-based statistics for the group of neurotypical children, as they didn’t undergo the assessment process.^[11]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

Caregiver questionnaires

Based on caregiver questionnaires, most autistic, clinical, and neurotypical children developed at least a moderate interest in letters and numbers during the study; and in fact, neurotypical children were more likely to show a moderate interest. But when it comes to an intense or even exclusive interest in letters and numbers, the prevalence was significantly higher in the autistic group (37% and 36%, compared to 25% and 24% in neurotypical children).^[12]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

Discrepancy

However, it should be noted that there is clearly a discrepancy between assessment reports and caregiver reports; compared to the caregiver questionnaires, assessment reports of the autistic children indicated a significantly lower prevalence of an intense interest in letters (20% compared to 37%) and numbers (17% compared to 36%). For the non-autistic ND children, the difference was even more dramatic, with a prevalence of 3% compared to 23% for an intense interest in letters, and a prevalence of 2% compared to 23% for an intense interest in numbers.^[13]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

The paper doesn’t explicitly explain the discrepancy between these two measures, but looking at how the assessments and caregiver questionnaires were conducted, it becomes clear that interest wasn’t measured in the same way; in the caregiver questionnaire, caregivers were asked to quantify the amount of time the child spends on engaging with letters and numbers by selecting from five options: Exclusive (70–100%), Majority (45–65%), Frequent (25–40%), Occasional (10–20%), and Absent (0–5%). Their answers were then simplified to a binary variable, where Exclusive and Majority were coded as ‘1’, indicating the presence of a special interest in letters or numbers; and the remaining options were coded as ‘0’, indicating an absence of a special interest.^[14]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024) It strikes me as problematic to consider 40% of time spent engaging with one particular interest as an absence of a special interest though.

For the assessment reports, however, there was no specific attempt made to quantify the children’s interest in letters and numbers. Rather, an interest was only reported if the assessor happened to account it during their assessment procedure. So it’s very possible that some children showed a special interest in letters or numbers, but that this just didn’t come up during the assessment procedure.

Conclusion

So I see problems with the methodology of both types of reports. It’s unfortunate that special interest in letters or numbers wasn’t explicitly measured in the assessment reports, and that there was no attempt made to assess the neurotypical children for their interest in letters or numbers. As for the caregiver questionnaire, I disagree with their threshold for how much time spent on letters and numbers constitutes a special interest. Additionally, it’s unfortunate that both types of reports didn’t quantify interest in the same way, so we can’t directly compare the results of both measures.

Having said that, what does become clear from both reports is that autistic children were more likely to show an intense interest in letters and numbers. I guess in that sense, the data is “good enough” to conclude that autistic children are on average much more interested in letters and/or numbers.

Behaviors related to interest in letters & numbers

The authors also explored behaviors related to interest in letters and numbers. Here are some of their findings:^[15]Enhanced interest in letters and numbers in autistic children (Ostrolenk et al., 2024)

• For 51% of autistic children, letters were “special” to them
• Autistic children engaged less in social reciprocity with respect to reading; they showed less of the following behaviors: pretending to read; bringing a book to be read by an adult; liking to read for others; often accepting to read with an adult
• Autistic children were less good at recognizing some written words, counting out loud, counting objects of the same category, and being able to count
• Autistic and otherwise neurodivergent children were more likely to: show an interest in letters on screens, place letters in alphabetical order, and show an interest in games with numbers or math
• Autistic children were less likely than non-autistic ND children to: pronounce the sounds that letters make, write numbers or mathematical symbols
• Autistic children were less likely than neurotypical children to: pretend to write, understand that we read from left to right

Below you can see diagrams of various behaviors in autistic (light blue), non-autistic neurodivergent (dark blue), and neurotypical (salmon) children.

The authors do caution that some of these differences may be attributed to age, which was not controlled for in these comparisons. In particular, the non-autistic ND children (the “clinical group”) were older on average.

Grapheme–color synesthesia

Finally, this is beyond the scope of the study, but I find it fascinating to learn that autistic children show more interest in letters and numbers, as this may contribute to why grapheme–color synesthesia (where letters and numbers are involuntarily associated with colors) is more common in autistic people. Synesthesia in general occurs in about 18.9% of autistic adults, compared to 7.22% in the general population.^[16]Is synaesthesia more common in autism? (Baron-Cohen et al., 2013) But more specifically, research shows that the extent of grapheme–color synesthesia is associated with autism-related perceptual features, including attention to detail and hypersensitivity.^[17]Perceptual processing links autism and synesthesia: A co-twin control study (van Leeuwen et al., 2021)

The reason I bring this up is because there has been some evidence that grapheme–color synesthesia may develop based on letter/number–color associations during early childhood, like certain toys or refrigerator magnets.^[18]Synesthetic Colors Determined by Having Colored Refrigerator Magnets in Childhood (Witthoft & Winawer, 2006) This is also supported by a different study which showed that there was a remarkable consistency in letter–color associations in their sample (‘R’ elicited red for 36%, ‘Y’ elicited yellow for 45%,, and ‘D’ elicited brown for 47%).^[19]A systematic, large-scale study of synaesthesia: implications for the role of early experience in lexical-colour associations (Rich, Bradshaw, & Mattingley, 2005) Although I imagine there is a genetic component to the development of synesthesia as well, I’m now wondering if the intense interest in letters and numbers could be mediating that development.

In other words, are autistic children more likely to develop synesthesia based on their intense interest in certain objects with particular sensory qualities? More specifically in this case, are they more likely to develop grapheme–color synesthesia based on their intense interest in letters and numbers during early childhood?

I’m just a single data point, but I am very interested in letters and numbers; and I do have very strong color associations with them. I don’t know how consistent these associations are, because the particular shapes of letters can impact the color I assign to them. But when I think of numbers in my head, I believe 1 is consistently blue, 2 is consistently yellow, 3 is consistently green, 4 is consistently red, 5 is consistently blue, and so forth. Looking at the artwork I created at the top of this article, I had to reduce the colors to our brand colors, and I deliberately didn’t include green for the illustration, but without thinking about it, I did end up making the 5 blue, and the 4 “red” (well, salmon, but it’s a stand-in for red in our color palette).

I’m curious, did you show an intense interest in letters and/or numbers as a child? Did that interest persist into adulthood? How does that interest come to expression today? And do you have strong color associations with letters or numbers?