Whatever you want to call them — stims, repetitive behaviors, stereotypies — the terms are more-or-less interchangeable, but it remains that they are of importance in how we think about autism. The repetitive behavior/restricted interests domain is essential to an autism diagnosis. Autistic people, when asked, mostly seem to believe this is an important part of autism. Strangely, very few people have undertaken empirical research to validate (or challenge) common ideas about the nature of stimming.

For those who don’t know: what is stimming? There’s actually some variation in what people consider stims, but I think most people would agree that it includes rhythmic, repetitive movements of the body such as rocking, hand flapping, and pacing. Many people include vocalizations such as grunting or whistling. Based on the conventional description of some autistic children having a fascination with parts of objects (like the wheels on a toy car), I feel manipulation of items such as fidget toys and spinners should be counted as well.

Of course, then we’re get into restricted interests territory. Restricted interests and repetitive behaviors are counted in the same “domain” in the DSM, along with sensory atypicalities. In my view, they blend into each other, forming a continuum — but more on that later.

If you asked me, I’d say there’s a lot we don’t know about this topic. A lot of people have beliefs, for sure, but there’s little to no real evidence. At least, not the kind of evidence you can cite.

Most of the knowledge that’s out there comes from the beliefs of autistic community members. Dr. Steven Kapp (who is, coincidentally, a friend) did a qualitative analysis of 31 autistic people’s opinions on stimming.¹ Nobody said they disliked their stimming; most people said they found it calming. The study thusly found that stimming most likely serves a regulatory function, and identified three factors that autistic people said caused their stimming behavior: overwhelming environment/sensory overload, noisy thoughts, and uncontainable emotion.

It’s interesting to me that nobody in this study mentioned under-stimulation of sensory input.¹ They seemed more to believe that stimulation in excess of a certain individual or situational threshold was the primary cause, and in this case the “stimulation” could be an internal stimuli (a thought or an emotion).

It’s such a simple theory that it seems baffling that nobody has really tested it. Why is that important? Well… sometimes, as humans, things aren’t what we expect them to be. I know a lot of people will react negatively to that sentiment, but I’m autistic too, so it really is an everyone thing. A lot of psychology (ex, cognitive psychology) is actually not self-evident, and may be counter-intuitive. For example, people are not particularly good at judging how they best learn. People overestimate the benefit of massed rehearsal (cramming for an exam) because they feel like it helps them remember more than spaced rehearsal (studying every night), even after seeing evidence that spaced rehearsal results in better task performance.²

Don’t get me wrong, metacognitive insight is valuable — it’s my own greatest weapon! — but it helps to have evidence to back it up. (Likewise, it helps to have qualitative information to back up empirical results.) So why don’t we have studies about this?

One study that has been done (although, again, not an empirical study) used Bayesian statistical principles to think about the mechanisms of cognition in autism.³ They concluded that autism features atypical accuracy of predictions — or, more precisely, that they did not use as much prior knowledge in their perception, leading to potentially more accurate perceptions of the world. However, this makes ambiguity and uncertainty very difficult to deal with. The authors use this framework to understand stimming as a means of reducing the uncertainty in the environment, and thereby reducing the sense of alarm or sensory overload experienced by that person.

As I mentioned, repetitive behaviors blend together with restricted interests. Something I’ve become interested in is the role of perseverative or repetitive thoughts and its relation to the role of repetitive behaviors. I explored this idea a little bit in my first paper,⁴ but I have yet to truly investigate my thoughts on the matter as much as I would like. Here’s my underlying theory: autistic children, as children, have both repetitive behaviors and repetitive thoughts. Normally, these two processes inhibit each other. This seems to corroborate well with the accounts of “noisy thoughts” being a precursor for stimming behaviors to control them.¹ However, when children with normative verbal ability become older, they stop doing repetitive behaviors — leading to increased repetitive thoughts, which my study found could be a risk factor for developing depression.⁴ This might explain, at least in part, why rates of depression are highest in autistic adults with more normative verbal ability. And it lines up quite well with what the autistic people in Kapp’s study said: they identified others’ tolerance of their stims as a matter of acceptance vs. devaluation.¹

Do you have any theories?

References

1. Kapp, S. K., Steward, R., Crane, L., Elliott, D., Elphick, C., Pellicano, E., & Russell, G. (2019). ‘People should be allowed to do what they like’: Autistic adults’ views and experiences of stimming. Autism, 23(7), 1782–1792. https://doi.org/10.1177/1362361319829628
2. Logan, J. M., Castel, A. D., Haber, S., & Viehman, E. J. (2012). Metacognition and the spacing effect: The role of repetition, feedback, and instruction on judgments of learning for massed and spaced rehearsal. Metacognition and Learning, 7(3), 175–195. https://doi.org/10.1007/s11409-012-9090-3
3. Pellicano, E., & Burr, D. (2012). When the world becomes “too real”: A Bayesian explanation of autistic perception. Trends in Cognitive Sciences, 16(10), 504–510. https://doi.org/10.1016/j.tics.2012.08.009
4. Keenan, E. G., Gotham, K., & Lerner, M. D. (2017). Hooked on a feeling: Repetitive cognition and internalizing symptomatology in relation to autism spectrum symptomatology. Autism, 2012, 136236131770960. https://doi.org/10.1177/1362361317709603