An experimental test of a person’s ability to understand that another person may have a different belief about a situation, one which differs from current reality and is thus ‘false’. This test involves a scenario enacted by two dolls called Sally and Anne and the movement of a marble when one is absent. The test is whether the person observing the scenario understands that the character who has been absent will not know that the marble is not in its original position. (See also Theory of Mind.)

A term used for those with profound difficulties in most areas who display an exceptional talent in one area such as art or music.

This is a condition, seen especially in children, in which a person does not speak or communicate effectively in situations where they do not feel comfortable, secure and relaxed. For instance, a child may not speak – or indeed attempt any communication – at school, yet do so at home with their close family. In many cases, selective mutism can be attributed to extreme social anxiety. When it occurs with autism, it may be part of a more fundamental communication problem.

A person’s capacity to reflect on their own thoughts, feelings and traits.

Sensory is important first one

Heightened sensitivity to sounds, tastes, visual and other stimuli, compared with what most people experience. Common in people on the autism spectrum. (See also sensory hyposensitivity.)

Reduced sensitivity to sounds, tastes, visual and other stimuli, compared with what most people experience. Common in people on the autism spectrum. (See also sensory hypersensitivity.)

Broadly defined as a state in which individuals are exposed to so many sensory stimuli, or to stimuli at such high intensities, that they become unable to deal with them. For instance, they may become very stressed and/or become unresponsive to sensory input. In autism, hypersensitivity to sensory stimuli means that a person may experience overload even for moderate levels of stimulation that would not be disagreeable for a person without autism.

The means by which we acquire information about the environment through specialised sense organs, each of which deals with a different modality or dimension of input (sound, smell, taste etc.).

A neurotransmitter involved in complex brain processes, including the regulation of mood, emotions, aggression, sleep and body temperature.

Relatively informal evaluation of an intervention which precedes a full-scale controlled trial. Small-scale evaluations involve testing the intervention with a small number of individuals and usually include observations before, during and after it has taken place.

This involves all forms of interaction between two or more people, ranging from the use of spoken language, facial expressions, gestures and body language to making friends and forming long-term relationships.

This approach to explaining the causes of behaviour, including the development of conditions such as autism, identifies children’s social environment as the key factor. This means influences such as parenting style and the quality of social and emotional interactions the child has with other people.

In relation to autism, this refers to an intense and focused interest in a particular subject or topic, which may in some cases seem unusual or eccentric. Autistic people often have just one or two special interests which they pursue for a long time. They may acquire very detailed knowledge or skill and approach their interest with an intensity that tends to exclude other subject matter. Yet evidence suggests that special interests can be beneficial.

A school or stand-alone unit whose main purpose is to provide education tailored to the additional support needs of children and young people with significant special educational needs. Some special schools are designed specifically for children on the autism spectrum, while others cater for a range of special needs. This definition refers to the UK, but similar provision exists in some other countries.

A health professional whose role is to assess and treat children and adults with speech, language and other communication difficulties.

This is where an individual has a skill in one specific area, such as numeracy or art, which does not characterise their overall abilities or level of functioning. For example, an individual with a low IQ may nonetheless be able to complete complex jigsaw puzzles. Very exceptional levels of such skill are referred to as savant talent. (See also savant talent.)

A legal document in Wales or Northern Ireland drawn up by the local authority, after specialist reports are obtained, which specifies the school-related support needs for a child or young person up to age 19.

A term meaning that the result from an experiment or evaluation of an intervention is highly unlikely to have occurred by chance. If the statistical probability of a chance result is calculated to be sufficiently low, the researcher may reasonably conclude that the result is due to the influence under investigation. For instance, the researcher may conclude that an intervention really has helped the individuals who have participated, or that autistic and neurotypical people really do differ in how they respond to sounds.

A short-hand term for self-stimulatory behaviour or self-stimulation. The repetition of physical movements and sounds, and the repetitive manipulation of objects, which are common in individuals with developmental conditions, and especially in autism, are thought to have pleasant self-stimulatory effects.

The use of emphasis within speech to mark particular words or phrases. Stress plays a role in communication, and may be atypical in people on the autism spectrum. (See also non-verbal communication.)

A survey is a research method in which questionnaire responses are gathered from a large sample of people. These responses are then analysed statistically, to establish trends in those sampled.

Features or characteristics that may indicate a clinical problem or disorder. In some medical conditions (e.g. flu), symptoms may be feelings that the individual experiences and reports to a doctor. In other conditions, such as autism, an individual's symptoms are more likely to be atypical behaviours observed by others such as the individual's parent, or a clinician. Symptoms form the basis for formal diagnostic classifications.

A small gap between two neurons where the transmission of signals takes place via neurotransmitters, chemical messengers that cross the gap.

A term denoting a characteristic combination of symptoms, usually assumed to be caused by a specific underlying disorder, even if the causal mechanism is not well understood. Many syndromes are named after the physicians credited with first reporting the association, hence Kanner's syndrome and Asperger syndrome. Autism is now considered more as a spectrum rather than specific syndromes.

Systemising is defined by Baron-Cohen as the drive to analyse or construct systems, where a system is any domain that lends itself to rules predicting or explaining how the domain works. The precise scope of this idea is vague: it is usually related to subject matter such as science, engineering and maths, but other domains could also be defined in terms of systems and rules. Baron-Cohen proposes that people with autism have a cognitive profile characterised by a high level of systemising ability, together with limited empathising ability. (See also empathising, Empathy Quotient (EQ) and Systemising Quotient (SQ).)

A questionnaire-based measure of systemising devised by Baron-Cohen and colleagues. A person’s overall test score on the SQ is assumed to reflect their ability to systemise. Each member of a population can receive a low, high or average score. On average, females tend to score lowest whereas people on the autism spectrum generally have high scores, although there is also considerable overlap. (See also empathising, Empathising-systemising theory, and systemising)