New Theories of Autism: Hyper-Systemizing and Assortative Mating

Simon Baron-Cohen, PhD, MPhil


December 29, 2005

In This Article


Change is a universal feature in the environment to which the brain must react. There are 2 types of structured change:

  1. Agentive change: If change in an object is perceived to be self-propelled, the brain interprets the object as an agent, with a goal.[11,12] Agentive change cannot easily be predicted except through empathy. To interpret agentive change, humans employ specialized neurocognitive mechanisms, collectively referred to as the "empathizing system."[13,14,15] The neural circuitry of empathizing is now quite well mapped.[8,9,10] Key brain areas involved in empathizing include the amygdala, the orbital and medial frontal cortex, and the superior temporal sulcus.

  2. Non-agentive change: Any structured change that is not self-propelled is interpreted by the brain as a non-agentive change. "Structured" means the change is non-random, that is, ea result of a precipitating event or some other pattern. The brain does not deploy the empathizing mechanisms to predict such change. Instead, the human brain engages in "systemizing"; it searches for structure (patterns, rules, regularities, periodicity) in data, to discern whether the changing data is part of a system. Systemizing involves observation of input-operation-output relationships, leading to the identification of laws to predict that event "X" will occur with probability (p).[16]

Some systems are 100% "lawful" (eg, an electrical light switch or a mathematical formula). Systems that are 100% lawful have zero variance, or no more than 1 degree of freedom, and can therefore be predicted (and controlled) 100% of the time. A computer might be an example of a 90% lawful system: the variance is wider or there are more degrees of freedom. The social world may be only 10% lawful. This is why systemizing the social world is of little predictive value.

Systemizing involves 5 phases:

Phase 1 - Analysis. Single observations of input and output are recorded in a standardized manner at the lowest level of detail.

Phase 2 - Operation. An operation is performed on the input and the change to the output is noted.

Phase 3 - Repetition. The same operation is repeated over and over again to test whether the same pattern between input and output is obtained.

Phase 4 - Law derivation. A law of the pattern is formulated if X (operation) occurs, A (input) changes to B.

Phase 5 - Confirmation/disconfirmation. If the same pattern of input-operation-output holds true for all instances, the law is retained. If a single instance does not fit the law, phases 2-5 are repeated, leading to modification of the law or a new law.

Systemizing non-agentive changes is effective because these are simple changes: the systems are at least moderately lawful, with narrow variance (or limited degrees of freedom). Agentive change is less suited to systemizing because the changes in the system are complex (wide variance, or many degrees of freedom).

The hyper-systemizing theory of ASC posits that all human brains have a systemizing mechanism (SM), and this is set at different levels in different individuals. In people with ASC, the SM is set too high. The SM is like a volume control. Evidence suggests that within the general population, there are 8 degrees of systemizing:

Level 1: Such individuals have little or no drive to systemize, and consequently can cope with rapid, unlawful change. Their SM is set so low that they hardly notice whether the input is structured or not. Although this would not interfere with their ability to socialize, it would lead to a lack of precision over detail when dealing with structured information. We can think of this as hypo-systemizing. Such a person would be able to cope with agentive change easily, but may be challenged when dealing with highly lawful non-agentive systems.

Levels 2 and 3: Most people have some interest in lawful non-agentive systems, and there are sex differences. More women in the general population have the SM at level 2, and more men are at level 3. Thus, women are more able to cope with agentive change than men. For example, on tests of map-reading or mental rotation or mechanics, or on the Systemizing Quotient (SQ), men perform higher than women do.[15,17,18,19]

Level 4: Level 4 corresponds to individuals who systemize at a higher-than-average level. Some evidence indicates that above-average systemizers have more autistic traits. Thus, scientists (who by definition have the SM set above average) score higher than non-scientists on the Autism Spectrum Quotient (AQ). Mathematicians score highest of all scientists on the AQ.[20] Parents of children with ASC also have higher-than-average SM set[21,22] and have been described as having the "broader phenotype" of autism. At level 4, one would expect a person to be talented at understanding systems with moderate variance or lawfulness.

Level 5: People with AS have an SM set at level 5; they can easily systemize lawful systems such as calendars or train timetables.[23] Experimental evidence for hyper-systemizing in AS includes the following:

  • People with AS score higher than average on the SQ[18];

  • People with AS perform at a normal or high level on tests of intuitive physics or geometric analysis[19,24,25,26];

  • People with AS can achieve extremely high levels in domains such as mathematics, physics, or computer science[27];

  • People with AS have an "exact mind" when it comes to art[28] and show superior attention to detail.[29,30]

Levels 6-8: The SM is set at level 6 in people with high functioning autism (HFA); level 7 in those with medium functioning autism (MFA); and the maximum level 8 in those with low functioning autism (LFA). Thus, people with HFA try to socialize or empathize by "hacking" (systemizing),[31] and on the picture-sequencing task, they perform above average on sequences that contain temporal or physical-causal information.[32] People with MFA perform above average on the false photograph task.[33] In those with LFA, obsessions cluster in the domain of systems, such as watching electric fans go round,[34] and given a set of colored counters, they show extreme "pattern imposition."[35]

The hyper-systemizing theory can also explain why some people with autism may possess more or less language skills, a higher or lower IQ, or differing degrees of mindblindness.[13] According to this theory, when the SM is turned downwards from the maximum level of 8, at each point on the dial the individual should be able to tolerate an increasing amount of change or variance in the system. Thus, if the SM is set at level 7, the person will be able to deal with systems that are less than 100% lawful, but still highly lawful. The child could achieve a slightly higher IQ (because there is a slightly greater possibility for learning about systems that are less than 100% lawful), and the child would have a slightly greater ability to generalize than someone with classic autism.[1] The higher the level of the SM, the less generalization,[36] because systemizing involves identifying laws that might only apply to the current system under observation.

At level 7, one would expect some language delay, but this might only be moderate (because someone whose SM is set at level 7 can tolerate a little variance in the way language is spoken and still see meaningful patterns). Furthermore, the child's mindblindness would be less than total. If the SM is set at level 6, such an individual would be able to deal with slightly less lawful systems. This would be expressed as only mild language delay, mild obsessions, mild delay in theory of mind, and stilted social behavior, such as attempts at systemizing social behavior.


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