Autism spectrum disorder (ASD) or ADHD

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Below you can read a detailed explanation of Autism Spectrum Disorder (ASD), especially the overlap and differences with ADHD.

I will try to give as much information as possible, in a clear way. The page, of course, starts with the theory and the main symptoms.

DSM-5 criteria for Autism spectrum disorder

According to the psychiatric manual DSM 5th version (Diagnostic and Statistical Manual of Mental Disorders), Autism Spectrum Disorder (ASD) has 2 main criteria groups: A and B.

A. Ongoing (persistent) deficiencies in social communication and social interaction, whether in the past or in the present day.

It therefore concerns shortcomings in contacts with other people (not with other animals). The following 3 criteria must be met:

  1. deficiencies in social-emotional reciprocity. That is, there are problems in sensing, starting, maintaining a normal conversation.
  2. deficiencies in the non-verbal communicative behavior used for social contacts/interactions.
  3. shortcomings in developing, maintaining and understanding relationships, both private and at work.

B. Restricted, repetitive patterns of behavior, interests, or activities, again reflected in an individual's history or present. At least 2 of the 4 criteria listed below must be met:

  1. Stereotypical or repetitive motor movements, or repetitive use of objects or repetitive spoken language.
  2. Stubborn adherence to the same behavior, pattern, situation; inflexible adherence to routines or ritualized patterns of (non)verbal behaviour
  3. Very limited, very fixed interests that are abnormally intense or focused.
  4. Over or under responding to sensory stimuli; or unusual interest in sensory elements of the environment.

C. The above symptoms must be present in early development or childhood.

D. The symptoms cause clinically significant distress or impairment in social, occupational, or daily life functioning.

E. The impairments are not better explained by intellectual disability or general developmental delay.

ADHD and autism spectrum disorder: overlap and differences

As explained on another page, an autism spectrum disorder (ASD) has clear prototypical features from a neuropsychological point of view. However, these can differ per person in intensity and quantity, making diagnosis more difficult.

But in the diagnosis of ASD you are still helped by focusing on the prototypical features of ASD. One of the strongest characteristics of ASD is that you then have problems with parts of social perception and communication. Often there are also problems in recognizing emotions or regulating one's own emotions.

See the graphic overview below.


Above: The negative features of ASD (right) and its suspected causes (left)

ADHD: Theory of Mind intact

In the image on the left, the disorder in the so-called Theory of Mind is seen as an important cause of communication problems in people with Autism Spectrum Disorder.

Frankly, the Theory of Mind is less well developed in many more people, so only this characteristic does not prove so well whether there is Autism. But it does say that for a diagnosis of Autism Spectrum Disorder, there must be obvious difficulties in perceiving and processing emotions as well as ideas of other people.

This is usually not the case in people with ADHD. There are communication problems in people with ADHD, but .... these are not due to the fact that the perception or processing of ideas or emotions of other people is disturbed.

For example, people with ADHD are indeed able to recognize signals of emotions in others, they also sense when they can or cannot say something and how they should say it in order not to come across as too blunt or hurtful.

However, the problem in communication in people with ADHD mainly lies in reduced concentration and often increased impulsiveness, as a result of which they pay less attention to the conversation partner. As a result, they can, for example, interrupt someone too impulsively in the conversation, or jump from one subject to another too quickly in their conversation, which can irritate the interlocutor. However, if this is returned as feedback, someone with ADHD can indeed adjust their listening attitude. Because the ability to empathize with an interlocutor is not the biggest problem here.

However, that is the case with someone with autism: they often do not understand what they have done wrong when they receive such feedback. Emotions are usually not well seen, not well understood by someone with autism, so that the feedback about this is often surprising for someone with autism. After all, he means well but the feedback suggests that he is doing it 'wrong' during a conversation.

ADHD: Emotional processing is intact

As can also be seen in the image above, ASD has a problem with perceiving and processing emotions. There are generally quite large differences between people in reading and processing emotions. So on the basis of this criterion alone it is extremely difficult to distinguish the two diagnoses from each other.'s always about the extremes here. In people with autism spectrum disorder, there are serious problems in the perception, processing and expression of emotions (=emotion regulation).

For example: picking up signals related to emotions such as sadness or fear is, on average, much worse in people with ASD than in 'normal' people or people with ADHD. For example, eye contact with ASD is often strange: sometimes it's too long (staring), sometimes it is changing too often, or someone does not look at the eyes, but mainly at e.g. the mouth or 1 eye only. In general, you can see that looking at someone's face is a bit uncomfortable for someone with ASD. If you ask this, people with ASD usually confirm this. That is not the case with people with ADHD.

People with ASD often have difficulty reading from a face which emotions are in play at that moment, at least, much worse than average. As said, this can also apply to many 'normal' people, but on average people with ASD really have much more trouble with this. For example, a face must indicate very clearly that there is for example fear or sadness. Only then can someone with ASD see such emotion much better. Someone with ADHD usually doesn't need such a very clear facial expression to correctly recognize an emotion.

In addition to problems in recognizing and interpreting nonverbal behavior in people with ASD, there is also a problem in recognizing emotions in language, both verbally and in writing. A word or phrase is often taken very literally by people with ASD. So if someone apps: "I was so good at tennis then that I even lost to beginners", then the joke or irony is often not recognized. Someone with ASD takes the sentence too literally and clearly sees "so good at tennis" and that doesn't match with the rest of the sentence. Someone with ASD then really gets  confused and is surprised and often gets angry. This does not apply to someone with ADHD.

Another example is that people with ASD need more signals to recognize the emotions in the language. So just seeing words or sentences in a Whatsapp message is often not enough. People with ASD must therefore hear from a voice, or see from a face, which emotion is at stake. Of course this also applies to many more 'normal' people, but ... with ASD this failure to recognize emotions is much more seriously affected. As a result, only emailing or texting is much riskier for people with ASD because it can more often lead to miscommunication and misunderstood messages.

ADHD and ASS: Deficiencies in information processing or executive functions

Here we encounter an area where there is much more overlap between ADHD and Autism Spectrum Disorder (ASD). Executive functions are the regulating functions of the brain: planning, organizing, impulse control, correcting oneself and seeing mistakes, changing planning and executing things in a structured way according to planning (which requires sustained attention).

You will find problems here with both ADHD and Autism Spectrum Disorder. To be honest: a malfunction in the executive functions actually occurs in almost all diagnoses. That is inherent in the definition of executive functions: they are the regulating, controlling functions of someone's behavior. With almost all emotional problems, there are by definition also problems in regulating behavior. can say that by definition there are problems to be found in the executive functions. However, if you start figuring this out neuropsychologically, through executive function tests, you don't always find it. This in turn has to do with the fact that there are very few good executive function tests in neuropsychology. More about this on another page on this website (under the heading Neuropsychology).

However, let me go through the parts of the executive functions step by step, for both ADHD and ASD.

ADHD and Autism: planning

For planned reasoning, insight is required, so knowledge of the facts, but also being able to distinguish between main and side issues and logical reasoning. People with ASD can generally do that much better than people with ADHD. They are more accurate, pay attention to much more detail and therefore will not make many mistakes. Their logical reasoning and persistence is also much better developed than in people with ADHD.

The organizational problems in people with autism are therefore not due to serious planning disorders, but because they often see too many details, find all details important and therefore do not properly see the overview and are not able to apply structure. Eventually they can do this, but this will take much longer than average and they will hardly make any mistakes.

In people with ADHD, you mainly see that they do not pay attention to all details, so they miss many things in their planning, make many more (careless) mistakes, and spend much more time correcting all these mistakes. Their planning at the end often contains many mistakes, missed details and is therefore bad. Although planning is very slow in people with ASD, when it is finished, it is often very good and accurate, without many errors.

People with ASD also notice that when planning and executing a plan, they often get very persistent. They have incredible perseverance, sustained attention and iron discipline. This is not the case with people with ADHD: they give up much more quickly on a complex assignment, and are much more easily distracted during planning, by their own thoughts or by other external stimuli. They also become irritated much faster and therefore concentrate even worse. In the end, they often do not complete their planning anymore, they drop out more quickly. In fact, in people with ADHD, their motivational system is much less developed than in people with autism spectrum disorder.

Autism and ADHD: Hyperfocus

There is often confusion about the attentional system in people with autism or ADHD. Especially when it comes to the concept of 'hyperfocus'.

Hyperfocus is nothing else but intense selective attention for several minutes. It occurs both in people with ADHD and people with ASD. So what's the biggest difference?

In people with ASD, selective and sustained attention is much better developed than in people with ADHD. They can easily direct their concentration (focus) to their tasks for a longer period of time, without being distracted too much. If they are distracted, they can also return to their task much more quickly and easily, so they can resume their concentration.

This is clearly not the case with ADHD: both selective and sustained attention are downright bad. People with ADHD are very quickly (often within a few seconds) distracted by their own (rapid) thoughts, but also by external stimuli (sounds, movements). They also cannot return  quickly to their focus or task, simply because they have already forgotten what they were doing. Their plan and course are therefore not so fixed in their working memory. So with every distraction, that plan quickly disappears from their working memory.

In people with ASD, their strength is that they can stick to one plan much more tightly. In fact, they find distractions very annoying and can therefore become emotionally upset, precisely because they want to follow their plan and cannot deviate from it. People with ADHD can often do that: deviate and quickly change plans. Their divided attention, doing things at the same time, is therefore much better developed than in people with ASD. People with ASD prefer to focus on one task instead of multiple tasks at the same time.

How is it possible that people with ADHD still have periods of 'hyperfocus'? These periods do indeed exist, but they are often triggered by the task requirements themselves, whereby it is also striking that such a task is very challenging and often has to take place at high speed. e.g. at a game. In a multi-player game, many things often happen at the same time, which means that attention is often drawn to the task requirements themselves. The hyperfocus in ADHD is therefore often not caused by the Internal Attention System (=endogenous attention) but by external stimuli (exogenous attention). In fact, the motivation to do such a task lies outside themselves.

However, people with ASD are better able to generate their intense focus (hyperfocus) themselves than people with ADHD. Their perseverance, intense passion for certain tasks, therefore causes their hyperfocus, which they can maintain longer than people with ADHD. They are also less likely to get bored than people with ADHD.

The motivational system (in which dopamine plays a major role) appears to be poorly developed in ADHD. In ASD, this system is usually well intact.

ADHD and ASS: Error recognition and self-correction

People with ASD generally have a much better perception of details and will therefore make few mistakes. This is completely different in people with ADHD: they have poor focus and will miss many more details and therefore make more mistakes.

The self-correcting capacity in people with ASD is therefore usually much better developed than in people with ADHD. The only reason that correcting errors is difficult for people with ASD is the fact that they spend a long time on a task, thus become fatigued and that increases errors. They will then become overstimulated and therefore more emotional and may therefore lose a lot of energy to correct the mistakes. Often this goes well, but after such an experience they are really exhausted.

In people with ADHD, the errors will not be corrected sufficiently, so there will be many more errors left, the work will be delivered more sloppy. They will also drop out more quickly, be more impatient and therefore also become emotionally overstimulated. They are also often dead tired afterwards.

ADHD and ASS: Cognitive flexibility

This seems to be a clear difference between people with ASD and ADHD. People with ASD are known to have a hard time with sudden changes. Once they have a plan in mind (and they always do), they cannot easily deviate from it. They find that very annoying and it also makes them very emotional, usually anxious and therefore also angry. Then they can even 'explode' or react in panic ('flapping' in children, walking back and forth restlessly).

People with ADHD prefer sudden changes to long boring tasks or schedules. They are more stimulus-hungry than people with ASD. This is because they are driven by external stimuli, which means they retain their motivation much longer. People with ASD do not really need these external stimuli to maintain their motivation and focus. In fact, too many external stimuli can make people with ASD more likely to become overstimulated (overtired).

In short: flexibility in tasks or thoughts is much more difficult for people with ASD than for people with ADHD.

ADHD and ASS: Hyperactivity

Restless movement or hyperactivity is mainly seen in people with ADHD. Often from being annoyed, understimulated. It is much less common in people with ASD. It can occur, but it is mainly caused by overstimulation. By moving more restlessly (often fixed movements, or fidgeting) people with ASD try to reduce their accumulated tension.

Impulsivity in ADHD and Autism

You will not see impulsivity as often in people with ASD as in people with ADHD. The interests of people with ASD and ADHD will not be very different: both are interested in all kinds of things. However, switching between interests is much more likely in people with ADHD because they can get bored much more quickly. They are understimulated more quickly: they need more external stimuli to focus on something or to experience pleasure. As a result, they appear to be more impulsive than people with ASD.

Impulsivity in social contacts is more common in people with ADHD than in people with autism. Here too, this is mainly due to faster boredom in people with ADHD. People with ADHD will also be more impulsive and usually they talk much faster than average. For example: they will change topics faster, interrupt someone faster, fill in sentences of others much faster in a conversation. Mainly because they are less able to inhibit themselves.

People with ASD will find it more difficult and often more annoying to change subjects quickly because they cannot change plans quickly. They can interrupt people quickly in a conversation, but not because they are impulsive, but they are enthusiastic about certain topics. However, they will not be able to sense when they can or may interrupt someone, without it being annoying for others. Their listening attitude will also suffer because they like to dive deeply into a topic, without feeling that that is not always what the interlocutor wants.

In summary

Below is a graphic overview of the differences and overlap between ASD and ADHD.

By the way: someone can have both Autism Spectrum Disorder (ASD) and ADHD. This happens especially if, in addition to the ASD symptoms, there are also too many symptoms of ADHD.

N.B.: However, I do believe that a very careful look should be taken at the causes of the symptoms. It may sometimes be that one underlying mechanism can explain almost all symptoms and then I am in favor of only 1 diagnosis and not 2 diagnoses. In my opinion, more diagnoses can also stigmatize someone even more.


Advices for diagnostics

1. Probing more questions

As has become clear, there are some overlaps between ADHD and ASD. Especially when it comes to the cognitive features. It is therefore very wise to ask for clear examples of everyday activities, especially under 'normal' circumstances.

People with ASD can especially show characteristics of ADHD under stress, so examples of behavior when they are themselves is very important.

2. The biggest differences between ADHD and ASD are in the social domain: there is more emotional reciprocity in people with ADHD. The social contact feels more normal than with ASD.

3. Asking about interests and professions that people have or have had can also help with the difference between people with ASD or ADHD. Professions in which many details have to be processed, often in a fixed, structured way, with as few mistakes as possible, are where people with autism are often found.

Questionnaires or tests for autism

This site contains a number of screeners (short questionnaires) and an extensive questionnaire for autism spectrum disorder. This latest extensive ASD questionnaire in particular clearly shows the 7 criteria of ASD in the report (as discussed above). Unfortunately, it is still in Dutch: the English version will be released in the next month.

If you want to know if you have enough traits of Autism Spectrum Disorder, you can complete this free extensive ASD questionnaire together with someone you know well. See Autism tests for this.

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