An early and intense interest in written material, known as hyperlexia, occurs in some autistic children, with an emphasis on letters and numbers and a decoding ability that far exceeds comprehension. This phenomenon is observed in up to 20% of children with autism and seems to indicate an alternative route for language development since many of them have difficulties in oral communication and less response to the human voice.
Early and intense interest in written material, together with a discrepancy between advanced reading ability and a more limited understanding of the content, has been identified early in some children with atypical development, and this profile has been called "hyperlexia".
Hyperlexia describes cases where the child has the ability to decode words that far exceed their understanding of what they read. This skill profile has been observed frequently in children with autism, appearing in approximately 6% to 20% of cases, depending on the criteria used for assessment.
In a previous systematic review, it was demonstrated that 84% of hyperlexia individuals are on the autistic spectrum, which may represent an extreme manifestation of interest and ability for written material common in individuals with autism.
Language development in typical children occurs primarily through social interactions, using oral communication as a basis, and involves the exchange of attention with other people.
For example, a child who looks at something that an adult is pointing to demonstrates joint attention, a fundamental skill for social communication and language learning. In contrast, autistic children may demonstrate less responsiveness and attention to the human voice, which may affect the development of spoken language.
Studies show that for a significant proportion of autistic children, joint attention is not a predictor of their language development.
This early characteristic of autism, of less responsiveness to the human voice, suggests that nonrelational sources (i.e., not dependent on interaction with other people) of language exposure may play an important role in their language development.
An increased interest in written material may therefore be an alternative pathway for the development of some components of language in autistic children.
In a recent survey of parents of autistic children with an average age of 9 years, approximately 30% of the children showed a special interest in numbers and reading.
Measuring this interest in reading can be difficult because existing measures were designed for typical children and generally focused on the enjoyment a child gets from reading with an adult. These measures do not capture well the interest in self-directed reading activities (that the child does alone) that are common among autistic children.
Current questionnaires to assess repetitive interests and behaviors in autism are also limited because they focus on adolescents and adults and often emphasize the negative aspects of these interests, such as rigidity and perseveration on a single topic.
This study seeks to better understand interest in written material in a large sample of accurately diagnosed children with autism and compare them with children without autism up to the age of 6 years.
Two studies were conducted. Study 1 analyzed the prevalence and intensity of interest in letters and numbers in a sample of children referred for a diagnostic evaluation for autism, comparing information from children with autism with that from children with other diagnoses.
Study 2 repeated the questions from Study 1, but through direct interviews with parents, investigating in more depth the timing of the emergence of these interests and their characteristics in comparison with children without autism and children with typical development, in addition to exploring the relationship between interest in reading and the development of oral language.
A total of 701 children (391 with autism and 310 without autism) under the age of 7 years participated in the study, all referred for diagnostic evaluation over four years. Statistical analyses were performed to assess the relationship between the diagnosis of autism and the level of interest in letters and numbers.
A subsample of 138 autistic children, 99 children without autism or other clinical conditions, and 76 typically developing children had their parents interviewed with detailed questionnaires. Statistical models analyzed the age at which letter and number of interests emerged and the relationship between diagnosis and level of interest.
The results of both studies show that between 22% and 37% of autistic children have an intense or exclusive interest in letters. Autistic children were 2.78 times more likely to have a high interest in letters and 3.49 times more likely to have a high interest in numbers compared to clinically non-autistic children of the same age.
This high interest was maintained even among autistic children who were minimally or nonverbal (76% of the sample). Furthermore, the age at which these interests emerged did not differ between autistic and typically developing children, and this interest was not related to the child's level of oral language.
Non-autistic children showed greater interest in letters in social contexts, such as reading with an adult.
Emergence of interest in letters and numbers by diagnostic group. The proportion of autistic children (green), clinically non-autistic children (purple), and typically developing children (yellow) by age at onset of interest (in months). a) Proportion showing interest in letters, written words, and reading by age. b) Proportion showing interest in numbers and mathematical symbols by age
This study has some limitations, such as the lack of detailed sociodemographic data and the use of telephone interviews with caregivers, which may introduce bias in the responses.
In summary, the early emergence of a strong interest in written material in autistic children occurs at a time when they have great difficulties in developing oral language.
This interest in written language, together with recent findings on the nonsocial development of oral language in some autistic children, suggests that language acquisition in autism may follow an alternative developmental path, different from the typical development based on social interactions.
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Enhanced interest in letters and numbers in autistic children
Alexia Ostrolenk, David Gagnon, Mélanie Boisvert, Océane Lemire, Sophie-Catherine Dick, Marie-Pier Côté & Laurent Mottron
Molecular Autism, volume 15, Article number: 26 (2024)
Abstract:
An intense and precocious interest in written material, together with a discrepancy between decoding and reading comprehension skills are defining criteria for hyperlexia, which is found in up to 20% of autistic individuals. It may represent the extreme end of a broader interest in written material in autism. This study examines the magnitude and nature of the interest in written material in a large population of autistic and non-autistic children. All 701 children (391 autistic, 310 non-autistic) under the age of 7 referred to an autism assessment clinic over a span of 4 years were included. Ordinal logistic regressions assessed the association between diagnosis and the level of interest in letters and numbers. A nested sample of parents of 138 autistic, 99 non-autistic clinical, and 76 typically developing (TD) children completed a detailed questionnaire. Cox proportional hazards models analyzed the age of emergence of these interests. Linear regressions evaluated the association between diagnosis and interest level. The frequency of each behaviour showing interest and competence with letters and numbers were compared. In the two studies, 22 to 37% of autistic children had an intense or exclusive interest in letters. The odds of having a greater interest in letters was 2.78 times higher for autistic children than for non-autistic clinical children of the same age, and 3.49 times higher for the interest in numbers, even if 76% of autistic children were minimally or non-verbal. The age of emergence of these interests did not differ between autistic and TD children and did not depend on their level of oral language. Non-autistic children showed more interest in letters within a social context. The study holds limitations inherent to the use of a phone questionnaire with caregivers and missing sociodemographic information. The emergence of the interest of autistic children toward written language is contemporaneous to the moment in their development where they display a strong deficit in oral language. Together with recent demonstrations of non-social development of oral language in some autistic children, precocious and intense interest in written material suggests that language acquisition in autism may follow an alternative developmental pathway.
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