4. AS/HFA is a disability because of its associated medical conditions
Another argument may be that AS/HFA should be viewed as a disability because it carries with it an increased risk of medical conditions, such as epilepsy or mental retardation. For example, in classic autism, epilepsy occurs in one third of cases and mental retardation (IQ below the average range) occurs in about three quarters of cases . However, such associated medical conditions are clearly not specific to AS/HFA, and it is AS/HFA-specific features that are under discussion. Epilepsy or mental retardation may be justifiably seen as disabilities. These will require separate examination. But is AS/HFA (which by definition involves no retardation) necessarily a disability?
One might argue that some associated conditions are clearly disabilities. An example is language impairment. Many young children with HFA have little language. In some cases this applies to both their expression and comprehension. The combination of an autistic lack of social interest, together with little or no language, can be seen as a major disadvantage in a world of other people. Even if we down-play the importance of sociability, the child can still be regarded as disabled in being delayed in developing the ability to make his or her needs known. But whilst the notion of a disability may reasonably apply to extreme cases, the earlier point remains valid: that individuals with HFA need not necessarily be viewed as disabled as most of them will develop enough language even after a delay.

5. AS/HFA is a disability because it involves special needs and extra support
Perhaps the most compelling reason for viewing AS/HFA as a disability is that such individuals clearly have special needs (they need to be recognised as different, may require different kinds of teaching methods or schooling, or specific kinds of treatment) and access to such support in the present legal framework only flows to the child and their family if the case can be made that autism is a disability. Special funding does not automatically flow simply because one regards the child as "different". Given this economic reality, one should not remove the term "disability" from the deion of AS/HFA without ensuring that extra provision would still be available even if the term "difference" was more appropriate. This is really an issue relating to social policy, health and education economics, and the legal system.
Characterising the underlying difference in AS/HFA
We turn next to consider two different models which attempt to characterise the dimension(s) along which AS/HFA differs from normality.
1. The Folk Psychology-Folk Physics Model
The first model suggests that the two relevant dimensions along which to characterise individuals with AS/HFA might be "folk psychology" and "folk physics". Folk psychology involves understanding how people work. Folk physics involves understanding how inanimate things work. The model assumes that all individuals on the autistic continuum show degrees of folk psychology impairment, whilst their folk physics may be intact or even superior, relative to their mental age . This model is shown in Figure 1.
insert Figure 1 here
Folk Psychology
There is plenty of evidence that people with autism spectrum conditions have degrees of difficulty in mind-reading, or folk psychology. There have been more than 30 experimental tests, the vast majority revealing profound impairments in the development of their folk psychological understanding. These are reviewed elsewhere but include deficits in: joint attention ; use of mental state terms in language ; production and comprehension of pretence ; understanding that "seeing-leads-to-knowing" ; distinguishing mental from physical entities ; making the appearance-reality distinction ; understanding false belief ; understanding beliefs about beliefs ; and understanding complex emotions . Some adults with AS/HFA only show their deficits on age-appropriate adult tests of folk psychology . This deficit in their folk psychology is thought to underlie the difficulties such children have in social and communicative development , and the development of imagination .
Folk Physics
Other evidence suggests that children with AS/HFA may not only be intact but also superior in their folk physics. First, clinical and parental deions of children with AS/HFA frequently refer to their fascination with machines [the paragon of non-intentional systems] . Indeed, it is hard to find a clinical account of autism spectrum conditions that does not involve the child being obsessed by some machine or another. Examples include extreme fascinations with electricity pylons, burglar alarms, vacuum cleaners, washing machines, video players, calculators, computers, trains, planes, and clocks. Sometimes the machine that is the of the child"s obsession is quite simple (e.g., the workings of drain-pipes, or the design of windows, etc.). A systematic survey of obsessions in such children has confirmed such clinical deions .
Of course, a fascination with machines need not necessarily imply that the child understands the machine, but in fact most of these anecdotes also reveal that children with autism have a precocious understanding, too. The child (with enough language, such as is seen in children with AS/HFA may be described as holding forth, like a "little professor", on their favourite subject or area of expertise, often failing to detect that their listener may have long since become bored of hearing more on the subject. The apparently precocious mechanical understanding, whilst being relatively oblivious to their listener"s level of interest, suggests that their folk physics might be outstripping their folk psychology in development. The anecdotal evidence includes not just an obsession with machines, but with other kinds of physical systems. Examples include obsessions with the weather (meteorology), the formation of mountains (geography), motion of the planets (astronomy), and the classification of lizards (taxonomy).
Leaving clinical/anecdotal evidence to one side, experimental studies converge on the same conclusion, that children with AS/HFA not only have an intact folk physics, they have accelerated or superior development in this domain (relative to their folk psychology and relative to their mental age, both verbal and nonverbal). First, using a picture sequencing paradigm, we found that children with autism performed significantly better than mental-age matched controls in sequencing physical-causal stories . The children with autism also produced more physical-causal justifications in their verbal accounts of the picture sequences they made, compared to intentional accounts. This study however did not involve a chronological age (CA) matched control group, so the apparent superiority in folk physics in autism may simply have reflected their higher CA.
Second, two studies have found that children with autism showed good understanding of a camera . In these studies, children with autism could accurately infer what would be depicted in a photograph, even though the photograph was at odds with the current visual scene. This contrasted with their poor performance on False Belief tests. The pattern of results by the children with autism on these two tests was interpreted as showing that whilst their understanding of mental representations was impaired, their understanding of physical representations was not. This pattern has been found in other domains . But the False Photo Test is also evidence of their folk physics outstripping their folk psychology and being superior to mental age (MA) matched controls.
Family studies add to this picture. Parents of children with AS also show mild but significant deficits on an adult folk psychology task, mirroring the deficit in folk psychology seen in patients with AS/HFA . This is assumed to reflect genetic factors, since AS/HFA appear to have a strong heritable component . On the basis of this model, one should also expect that parents of children with autism or AS to be over-represented in occupations in which possession of superior folk physics is an advantage, whilst a deficit in folk psychology would not necessarily be a disadvantage. The paradigm occupation for such a cognitive profile is engineering.
A recent study of 1000 families found that fathers and grandfathers (patri- and matrilineal) of children with autism or AS were more than twice as likely to work in the field of engineering, compared to control groups . Indeed, 28.4% of children with autism or AS had at least one relative (father and/or grandfather) who was an engineer. Related evidence comes from a survey of students at Cambridge University, studying either sciences (physics, engineering, or maths) or humanities (English or French literature). When asked about family history of a range of psychiatric conditions (schizophrenia, anorexia, autism, Down Syndrome, language delay, or manic depression), the students in the science group showed a six-fold increase in the rate of autism in their families, and this was specific to autism .
Finally, children with AS have been found to perform at a superior level on a test of folk physics , and some adults with AS have reached the highest levels in physics and mathematics, despite their deficits in folk psychology .
2. The central coherence model
The Folk Psychology-Folk Physics Model is not the only attempt to capture the relevant dimensions underlying the autistic spectrum. A second model suggests the relevant dimension may be from weak to strong central coherence. Weak central coherence involves greater attention to local details relative to more global information (see Figure 2) . Central coherence is a slippery notion to define. The essence of it is the normal drive to integrate information into context, gist, gestalt, and meaning. Frith argues that the autistic person"s superior ability on the Embedded Figures Test and on an unsegmented version of the Block Design subtest in the Wechsler Intelligence Scale for Children (WISC) and Wechsler Adult Intelligence Scale (WAIS) arises because of a relative immunity to context effects in autism . Happe also reports a failure, by people with autism, to use context in reading, such that homophones are mispronounced [e.g., "There was a tear in her eye" might be misread so as sound like "There was a tear in her dress"] . A recent study has shown that children with autism are equally good at judging the identity of familiar faces in photographs, whether they are given the whole face or just part of the face. Non-autistic controls show a "global advantage" on such a test, performing significantly better when given the whole face, not just the parts of the face . The central coherence account of autism is attractive in having the potential to explain the nonholistic, piecemeal, perceptual style characteristic of autism, and the unusual cognitive profile seen in this condition (including the islets of ability). Recently, work in visual search has shown that individuals with autism spectrum conditions may be superior in their ability to make fine discriminations of targets from distractors . Such work may help take forward the concept of weak central coherence.
insert Figure 2 here
Note that these two models (Folk Psychology-Folk Physics; and Central Coherence) are not necessarily incompatible, since it is possible to imagine how weak central coherence could cause superior folk physics, as well as difficulties in folk psychology. Jarrold reports that in normal individuals, folk psychology and central coherence are indeed inversely correlated .
Whatever the relevant model, the dimensional approach is useful in reminding us that AS/HFA may simply be part of quantitative variation and individual differences in cognitive profiles, or styles of information processing. This approach could be re-cast to avoid the implication that one style is better (stronger) or worse (weaker), or that one is intact and another deficient. For example, the terms "weak" and "strong" central coherence are sometimes replaced by the more neutral terms, "local" vs "global" processing (referring to whether one spends more time processing at one level than another). See Figure 3.
insert Figure 3 here
The advantage of both of these models is that individuals with AS/HFA are understood in terms of an underlying dimension, and that this dimension blends seamlessly with normality, so that we are all situated somewhere on the same continuum. Most importantly, to reiterate, one"s position on the continuum is said to reflect a different cognitive style . Dimensional models also do not require a line to be drawn between ability and disability. Finally, they avoid the notion that individuals with AS/HFA are in some sense qualitatively different from those without AS/HFA. Such a notion is increasingly hard to defend in the light of intermediate cases. These are easier to accommodate in terms of quantitative variation.
Implications for understanding the apparent increase in prevalence of AS/HFA
There are some reports that AS/HFA is increasing in prevalence . It is unclear if this simply reflects better detection or if there is a genuine increase. However, if there is a genuine increase, this presents something of a paradox for the disability view: disabilities with a genetic basis which affect social skill and thus potentially reduce mating opportunities should be subject to negative selective pressures. Such disabilities should therefore be expected to reduce in prevalence with time. In order to be on the increase, such genes would have to be being positively selected. Increased prevalence presents no difficulties for the difference view however, since a cognitive style can at different times or under different conditions confer advantages to the individual. For example, the computer revolution in the 20th Century has created unprecedented opportunities for employment and economic prosperity for individuals with superior folk physics. This may have had positive effects on the reproductive fitness of such individuals, leading to an increase in the genes for AS/HFA in the gene pool. Such a speculation is testable: for example, one would predict higher rates of AS/HFA in the children of couples living in environments which function as a niche for individuals with superior folk-physics abilities (e.g."Silicon Valley", MIT, Caltech) compared to environments where no such niche exists. Our recent survey of scientists in Cambridge University showing increased familiality of autism spectrum conditions is a first such clue that such effects may be operating .
Summary
In a world where individuals are all expected to be social, people with AS/HFA are seen as disabled. The implication is that if environmental expectations change, or in a different environment, they may not necessarily be seen as disabled. As we have known in relation to other conditions, concepts of disability and handicap are relative to particular environments, both cultural and biological . It may be time to extend this way of thinking to the field of AS/HFA. We could imagine, for example, people with AS/HFA might not necessarily be disabled in an environment in which they can exert greater control of events. The social world is very hard to control, whilst the technological world of machines is in principle highly controllable. Equally, people with AS/HFA might not necessarily be disabled in an environment in which an exact mind, attracted to detecting small details, is an advantage. In the social world there is no great benefit to such a precise eye for detail, but in the world of maths, computing, cataloguing, music, linguistics, craft, engineering or science, such an eye for detail can lead to success rather than disability. In the world of business, for example, a mathematical bent for estimating risk and profit, together with a relative lack of concern for the emotional states of one"s employees or rivals, can mean unbounded opportunities.
It is hoped that this article, at the dawn of the new millennium, will open the debate towards identifying if there are any arguments for necessarily viewing AS/HFA as disabilities. In this article, none are found to apply persuasively to AS/HFA, even if they may apply to the "lower-functioning" cases. In contrast, the arguments in favour of viewing AS/HFA as a "difference" are more compatible with the "continuum" notion, and may be morally more defensible. The sole reason for retaining the term disability in relation to AS/HFA may be to ensure access to provision; it may be the legal system that needs revision, so that a child whose autistic "difference" leads them to have special needs, will still receive special support.
Figure Legends
Figure 1: This first model shows the relationship between Folk Physics (or understanding how things work) and Folk Psychology (or understanding how people work). For shorthand, folk psychology is referred to as "empathy", and folk physics is referred to as "scientist". Note that this is not the same as the ordinary usage of the word "scientist", as folk physics includes everyday understanding of s that is not necessarily the result of formal teaching. Individuals with AS/HFA are conceptualized as comprising types A-J.
Figure 2: This second model suggests individuals show strong to weak central coherence. Individuals with AS/HFA may be at the extreme left of this distribution .
Figure 3: This third model redescribes the second model in less value-laden terminology. Individuals are seen as showing local to global information processing styles. Again, individuals with AS/HFA may be at the extreme left of this distribution, spending relatively more time processing detail rather than processing in a broad-brush approach .
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