AutisticI children frequently show a delay in their language development1. It is, among other signs, one of the things that gets parents wondering whether their child might need additional educational support. Some autistic people, around 30%, are not able to communicate verbally2 even in adulthood. Does this mean that their language system differentiates them from non-autistic people? 

It is the case that one of the hallmarks of autism is experiencing difficulties in social communication3, such as misunderstandings, feeling that interactions are confusing and uncomfortable, and the anxiety and frustration that comes with that. However, autism is not regarded as a language disorder. If you did the math just now, you would know that 70% of autistic people reach verbal communication ability. Thus, autism is different from what is called Developmental Language Disorder, because of the other differences they show compared to non-autistic people in social interaction, repetitive behaviors (e.g., hand-flapping, fidgeting, routines and rituals), and intense or fixated interests. 

Then where does this language delay in autism come from? From studies observing autistic children, we know that they already show reduced attention in social situations from 12 months of age. We see this in the fact that they respond less to their name being called, look less in the direction someone is pointing, and spend more time looking at geometric shapes than faces4,5,6 in comparison to neurotypical children of the same age. In line with this, they also ask less for attention from other people7. When you engage less in social interaction, you in turn get less exposure and experience in language. A study that confirms this idea found that autistic children’s attention to social situations predicted how their language skills developed later on8. An additional explanation of the language delay in autism is that intellectual disability occurs in 20-30% of autistic people, and that intellectual ability is strongly related to language skills9. So it seems that the lack of language experience and intellectual disability play an important role in the language delay that autistic people experience. 

You may still wonder what is underlying the difficulties that autistic people experience in social interaction on a day-to-day basis, if not language. It has been suggested that autistic people are less motivated to engage in social interaction10. Yet, autistic people show different motivation for both social and non-social rewards11. Therefore, this differential motivation is not specific to social interaction. It is also important to consider that autistic children and adults show social motivation in different ways than non-autistic people do, for example with touch, communicating through writing, and interacting with objects as mediators11,12,13. Another prominent theory on the communicative difficulties in autism is an impaired ability to infer what other people are thinking or feeling, also known as Theory of Mind14. Recent evidence, however, suggests that this ability might be altered in some but not all autistic people and not in all situations15,16. Autistic people may take into account other people’s beliefs when being asked about it explicitly just as much as non-autistic people17. However, they might do this less in a spontaneous manner. Yet, this spontaneous form of taking another person’s perspective is in fact what we do in conversations everyday. Therefore, more research is needed into the behavior and experience of autistic and non-autistic people in situations that are close to real-life communication, rather than reading words in a research lab room, to find the answer to this question. 

In addition to psychological theories, researchers are also looking to find genetic differences in autistic people. From research in twins, we know that when one twin is autistic, the chance is very high that the other twin is as well18,19. This tells us that autism is highly heritable. It is very difficult, however, to point to one or multiple genes that can be identified as the cause of autistic behavior. This is partly the case because autistic people vary a lot in terms of the difficulties they experience and how much they experience them. Moreover, many autistic people have co-occurring conditions such as intellectual disability or ADHD. This also contributes to the variation in autism symptoms. To identify genes that are associated with this condition, it will be necessary to have access to detailed information on behavior, biology and genetics of thousands of people and their relatives20.  

From decades of research, we see that many autistic children start to speak later than their non-autistic peers. However, it is clear that a delay in language development is not the cause or the one defining feature of autism. More and better-designed experiments will teach us what the underlying differences are between autistic and non-autistic people. With this new knowledge we will be able to accommodate and support people at all levels on the autism spectrum in a better way.


I. In this article, I use ‘autistic children and people’ to refer to individuals on the autism spectrum. This term is preferred by many people in the autistic community.18


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