SGDP Research Centre, Institute of Psychiatry London, United Kingdom
The theory of mind account of autism suggests that children and adults with autism have difficulty understanding the thoughts and feelings of others. This account has been useful in making specific predictions about preserved and impaired abilities. For example, not all aspects of socialization require the ability to think about thoughts. Indeed, recent research has shown that not all aspects of socialization are impaired in people with autism - autism may be best thought of not as an impairment of sociability, but as an impairment of social ability. The idea that people with autism are "mind-blind", then, has been useful both theoretically and practically. However, the theory of mind account of autism cannot explain everything about autism. Two questions, in particular, remain: How is it that some people with autism do pass theory of mind tests? How can we explain the non-social handicaps (and skills) shown by many people with autism? In this paper I will discuss these questions and propose that some possible answers may lie in the idea that people with autism have weak "central coherence".
Autism is currently defined at the behavioural level, on the basis of impairments in socialization, communication, and imagination, with stereotyped repetitive interests taking the place of creative play (DSM-III-R, APA 1987). Psychological accounts of autism seek to explain this set of co-occurring symptoms in terms of underlying cognitive features, which in turn result from the multiple biological causes implicated in the disorder (Gillberg & Coleman, 1992). By thinking about what is different in the mind of the individual with autism, we aim to make causal links between the behavioural symptoms of autism and the presumed biological origins (Schopler & Mesibov, 1987) of the disorder.
One currently influential account of autism began in the mid-eighties, and sprang out of studies on the young child's developing social understanding. Baron-Cohen, Leslie and Frith (1985) hypothesized that individuals with autism lack a "theory of mind"; the somewhat misleading term used by Premack (Premack & Woodruff, 1978) for the ability to attribute independent mental states to self and others to predict and explain actions. This hypothesis was in part motivated by Leslie's analysis of the cognitive abilities underlying the normal 2-year-old's understanding of pretense and make-believe (Leslie, 1987, 1988) - together with the observation that children with autism show impairments in imagination (Wulff, 1985). This led to the hypothesis that autism might constitute a specific impairment in the cognitive mechanism necessary for representing mental states, or "mentalising". Leslie has suggested that this mechanism may be innate and discrete (the "theory of mind module", ToMM), hence allowing damage to this function in an individual with otherwise normal intelligence.
The first test of this theory required subjects to recognize a character's false belief in the "Sally-Ann" task (a variant of Wimmer & Perner's, 1983, Maxi task). Here the child sees Sally (a doll) hide a marble in her basket and leave the room, after which Ann moves the marble to her own box. The child is asked control memory questions and the key test question, "Where will Sally look for the marble?". Baron-Cohen, Leslie and Frith found that 80% of their sample of children with autism answered incorrectly - that Sally would look in the box, where the marble really is. By contrast, most normally-developing 4-year-olds, and 86% of a group of children with Down Syndrome, replied correctly that Sally would look in the basket where she mistakenly believes the marble to be. This finding was taken as evidence for an autism-specific deficit in thinking about thoughts, i.e.,. "mentalising".
The idea that people with autism have difficulty understanding the thoughts and feelings of others, has been useful to the study of autism in a number of ways. "Mind-blindness" would appear to account well for the triad of social, communication and imagination impairments shown by people with autism at all ages (Wing & Gould, 1978). Not only does it shed light on this triad, but it also makes "fine cuts" within the triad of autistic impairments. Social and communicative behaviour is not all of one piece, when viewed from the cognitive level. Some, but not all, such behaviour requires the ability to "mentalise" (represent mental states). So, for example, social approach need not be built upon an understanding of others' thoughts - indeed Hermelin and O'Connor (1970) demonstrated to many people's initial surprise that children with autism prefer to be with other people, just like non-autistic children of the same mental age. However, sharing attention with someone else does require mentalising - and is consistently reported by parents to be missing in the development of even able children with autism (Newson, Dawson and Everard, 1984).
The mentalising-deficit account has allowed a systematic approach to the impaired and unimpaired social and communicative behaviour of people with autism. The hypothesis that people with autism lack mentalising ability, has the power to make fine cuts in the smooth continuum of behaviours. It has sparked an enormous amount of research, both supporting and attacking the theory (reviewed by Happe, 1994d; Baron-Cohen, Tager-Flusberg & Cohen, 1993; Happe, 1994a).
The mentalising account has helped us to understand the nature of the autistic impairments in play, social interaction and verbal and nonverbal communication - but there is more to autism than the classic triad of impairments.
Clinical impressions, originating with Kanner (1943) and Asperger (1944; translated in Frith, 1991), and withstanding the test of time, include the following:
All of these non-triad aspects of autism are vividly documented in the many parental accounts of the development of children with autism (Park, 1967; Hart, 1989; McDonnell, 1993). None of these aspects can be well explained by a lack of mentalising.
Of course, clinically striking features shown by people with autism need not be specific features of the disorder. However, there is also a substantial body of experimental work, much of it predating the mentalising theory, which demonstrates nonsocial abnormalities which are specific to autism. Hermelin and O'Connor were the first to introduce what was in effect a different "fine cuts" method (summarized in their 1970 monograph) - namely the comparison of closely matched groups of subjects with autism and those with mental handicap (but not autism) of the same mental age. Table 1 summarizes some of the relevant findings.
Table 1 Experimental findings not accounted for by mind-blindness
Surprising advantages and disadvantages on cognitive tasks, shown by autistic subjects relative to normally expected asymmetries
|Unusual Strength||Unusual Weakness|
|memory for word strings||memory for sentences (eg. Hermelin & O'Connor, 1967)|
|memory for unrelated items||memory for related items (eg. Tager-Flusberg, 1991)|
|echoing nonsense||echoing with repair (eg. Aurnhammer-Frith, 1969)|
|pattern imposition||pattern detection (eg. Frith, 1970 a,b)|
|jigsaw by shape||jigsaw by picture (eg. Frith & Hermelin, 1969)|
|sorting faces by accessories||sorting faces by person (eg. Weeks & Hobson, 1987)|
|recognizing faces upside-down||recognizing faces right-way-up (eg. Langdell, 1978)|
The mentalising deficit theory of autism, then, cannot explain all features of autism. It also cannot explain all people with autism. Even in the first test of the hypothesis (Baron-Cohen et al, 1985), some 20% of the autism group passed the Sally-Ann task. Most of these successful children also passed another test of mentalising - ordering picture stories involving mental states (Baron-Cohen, Leslie & Frith, 1986) - suggesting some real underlying competence in mentalising. Baron-Cohen (1989a) tackled this apparent disconfirmation of the theory, by showing that these talented children still did not pass a harder ("second-order") theory of mind task (requiring them to understand what Mary thinks John thinks). However, results from other studies focusing on high-functioning people with autism (Bowler, 1992; Ozonoff, Rogers & Pennington, 1991), have shown that some such people can pass theory of mind tasks consistently, applying these skills across domains (Happe, 1993) and showing evidence of insightful social behaviour in everyday life (Frith, Happe & Siddons, 1994). One possible way of explaining the persisting autism of these successful subjects is to postulate an additional and continuing cognitive impairment. What could this impairment be?
The recent interest in executive function deficits in autism (Hughes & Russell, 1993; Ozonoff, Pennington & Rogers, 1991) can be seen as springing from some of the limitations of the theory of mind view discussed above. Ozonoff, Rogers & Pennington (1991) found that while not all subjects with autism and/or Asperger's syndrome showed a theory of mind deficit, all were impaired on the Wisconsin Card Sorting Test and Tower of Hanoi (two standard tests of the executive functions of set-shifting, inhibition, and planning). On the basis of this finding they suggest that executive function impairments are a primary causal factor in autism. However, the specificity, and hence the power of this theory as a causal account, has yet to be established by systematic comparison with other non-autistic groups who show impairments in executive functions (Bishop, 1993). While an additional impairment in executive functions may be able to explain certain (perhaps non-specific) features of autism (eg. stereotypes, failure to plan, impulsiveness), it is not clear how it could explain the specific deficits and skills summarized in table 1.
Motivated by the strong belief that both the assets and the deficits of autism spring from a single cause at the cognitive level, Frith (1989) proposed that autism is characterized by a specific imbalance in integration of information at different levels. A characteristic of normal information-processing appears to be the tendency to draw together diverse information to construct higher-level meaning in context; "central coherence" in Frith's words. For example, the gist of a story is easily recalled, while the actual surface form is quickly lost, and is effortful to retain. Bartlett (1932), summarizing his famous series of experiments on remembering images and stories, concluded: "...an individual does not normally take [such] a situation detail by detail... In all ordinary instances he has an overmastering tendency simply to get a general impression of the whole; and, on the basis of this, he constructs the probable detail" (p.206). Another instance of central coherence is the ease with which we recognize the contextually-appropriate sense of the many ambiguous words used in everyday speech (son-sun, meet-meat, sew-so, pear-pair). A similar tendency to process information in context for global meaning is also seen with nonverbal material - for example, our everyday tendency to misinterpret details in a jigsaw piece according to the expected position in the whole picture. It is likely that this preference for higher levels of meaning may also characterize mentally handicapped (non-autistic) individuals - who appear to be sensitive to the advantage of recalling organized versus jumbled material (eg. Hermelin & O'Connor, 1967).
Frith suggested that this universal feature of human information processing was disturbed in autism, and that a lack of central coherence could explain very parsimoniously the assets and deficits shown in table 3. On the basis of this theory, she predicted that subjects with autism would be relatively good at tasks where attention to local information - relatively piece-meal processing - is advantageous, but poor at tasks requiring the recognition of global meaning. An interesting example is the processing of faces, which seems to involve both featural and configural processing (Tanaka & Farah, 1993). Of these two types of information, it appears to be configural processing which is disrupted by the inverted presentation of faces (Rhodes, Brake & Atkinson, 1993; Bartlett & Searcy, 1993). This may explain the previously puzzling finding that subjects with autism show a diminished disadvantage in processing inverted faces (Langdell, 1978; Hobson, Ouston & Lee, 1988). The advantages of featural processing may disappear, however, when it is emotional expression which must be recognized - here configural processing may be necessary, making recognition of emotions relatively hard for people with autism.
A first striking signpost towards the theory appeared quite unexpectedly, when Amitta Shah set off to look at putative perceptual impairments in autism, using the Embedded Figures Test. The children were almost better than the experimenter! Twenty subjects with autism (average age 13, nonverbal mental age 9.6), were compared with 20 learning disabled children of the same age and mental age, and 20 normal 9-year-olds. These children were given the Children's Embedded Figures Test (CEFT, Witkin et al, 1971), with a slightly modified procedure including some pretraining with cut-out shapes. The test involved spotting a hidden figure (triangle or house shape) among a larger meaningful drawing (eg. a clock). During testing children were allowed to indicate the hidden figure either by pointing or by using a cut-out shape of the hidden figure. Out of a maximum score of 25, the children with autism got a mean of 21 items correct, while the two control groups (which did not differ significantly in their scores) achieved 15 or less. Gottschaldt (1926) ascribed the difficulty of finding embedded figures to the overwhelming "predominance of the whole". The ease and speed with which children with autism group picked out the hidden figure in Shah & Frith's (1983) study was reminiscent of their rapid style of locating tiny objects (eg. thread on a patterned carpet) and their immediate discovery of minute changes in familiar lay-outs (eg. the arrangement of cleaning materials on a bathroom shelf), so often described anecdotally.
The study of embedded figures was introduced into experimental psychology by the Gestalt psychologists, who believed that an effort was needed to resist the tendency to see the forcefully created gestalt at the expense of the constituent parts (Koffka, 1935). Perhaps, this struggle to resist overall gestalt forces does not occur for individuals with autism. If people with autism, due to weak central coherence, have privileged access to the parts and details normally securely-embedded in whole figures, then novel predictions could be made about the nature of their islets of ability.
The Block Design subtest of the Wechsler Intelligence Scales (Wechsler, 1974, 1981) is consistently found to be a test on which people with autism show superior performance relative to other subtests, and often relative to other people of the same age. This test, first introduced by Kohs (1923), requires the breaking up of line drawings into logical units, so that individual blocks can be used to reconstruct the original design from separate parts. The designs are notable for their strong gestalt qualities, and the difficulty which most people experience with this task appears to relate to problems in breaking up the whole design into the constituent blocks. While many authors have recognized this subtest as an islet of ability in autism, this fact has generally been attributed to intact or superior general spatial skills (Lockyer & Rutter, 1970; Prior, 1979). Shah and Frith (1993) suggested, on the basis of the central coherence theory, that the advantage shown by subjects with autism is due specifically to their ability to see parts over wholes. They predicted that normal, but not autistic, subjects would benefit from pre-segmentation of the designs.
Twenty people with autism, 33 normal and 12 learning disabled subjects took part in an experiment, where 40 different block designs had to be constructed from either whole or presegmented drawn models. Subjects with autism who had normal or near-normal nonverbal IQ were matched with normal children of 16 years. Subjects with autism who had nonverbal IQ below 85 (and not lower than 57) were compared with learning disabled children of comparable IQ and chronological age (18 years), and normal children aged 10. The results showed that autistic skill on this task results from a greater ability to segment the design. Subjects with autism showed superior performance compared to controls in one condition only - when working from whole designs. The great advantage which the control subjects gained from using pre-segmented designs was significantly diminished in the autism group, regardless of their IQ level. On the other hand, other conditions which contrasted presence and absence of obliques, and rotated versus unrotated presentation, affected all groups equally. From these latter findings it can be concluded that general visuo-spatial factors show perfectly normal effects in subjects with autism, and that superior general spatial skill cannot account for Block design superiority.
While weak central coherence confers significant advantages in tasks where preferential processing of parts over wholes is useful, it would be expected to confer marked disadvantages in tasks which involve interpretation of individual stimuli in terms of overall context and meaning. One case in which the meaning of individual stimuli is changed by their context is in the disambiguation of homographs. In order to choose the correct (context-appropriate) pronunciation in the following sentences, one must process the final word as part of the whole sentence meaning; "He had a pink bow", "He made a deep bow", In her eye there was a big tear, In her dress there was a big tear. Frith & Snowling (1983) predicted that this sort of contextual disambiguation would be problematic for people with autism. They tested 8 children with autism who had reading ages of 8 to 10 years, and compared them with 6 dyslexic children, and 10 normal children of the same reading age. The number of words read with the contextually-appropriate pronunciation ranged from 5 to 7 out of 10 for the children with autism, who tended to give the more frequent pronunciation regardless of sentence context. By contrast, the normal and dyslexic children read between 7 and 9 of the 10 homographs in a contextually-determined manner. This finding suggested that children with autism, although excellent at decoding single words, were impaired when contextual cues had to be used. This was also demonstrated in their relative inability to answer comprehension questions and to fill in gaps in a story text. This work fits well with previous findings (table 1) concerning failure to use meaning and redundancy in memory tasks.
The hypothesis that people with autism show weak central coherence aims to explain both the glaring impairments and the outstanding skills of autism as resulting from a single characteristic of information processing. One characteristic of this theory is that it claims that the islets of ability and savant skills are achieved through relatively abnormal processing, and predicts that this may be revealed in abnormal error patterns. One example might be the type of error made in the Block Design test. The central coherence theory suggests that, where errors are made at all on Block Design, these will be errors which violate the overall pattern, rather than the details. Kramer et al (1991) found that in normal adult subjects there was a strong relation between the number of such configuration-breaking errors made on the Block design test and the number of local (versus global) choices made in a similarity-judgment task (Kimchi & Palmer, 1982). Preliminary data from subjects with autism (Happe, in preparation) suggest that, in contrast to normal children, errors violating configuration are far more common than errors violating pattern details in autistic Block Design performance.
A second example concerns idiot savant drawing ability. Excellent drawing ability may be characterized by a relatively piece-meal drawing style. Mottron & Belleville (1993) found in a case study of one man with autism and exceptional artistic ability, that performance on three different types of tasks suggested an anomaly in the hierarchical organization of the local and global parts of figures. The authors observed that the subject "began his drawing by a secondary detail and then progressed by adding contiguous elements", and concluded that his drawings showed "no privileged status of the global form...but rather a construction by local progression". In contrast, a professional draughtsman who acted as a control started by constructing outlines and then proceeded to parts. It remains to be seen whether other savant abilities can be explained in terms of a similarly local and detail-observant processing style.
Central coherence then may be helpful in explaining some of the real-life features that have so far resisted explanation, as well as making sense of a body of experimental work not well accounted for by the mentalising deficit theory. Can it also shed light on the continuing handicaps of those talented people with autism who show consistent evidence of some mentalising ability? Happe (1991, 1997), in a first exploration of the links between central coherence and theory of mind, used Snowling & Frith's (1986) homograph reading task with a group of able individuals with autism. Subjects with autism were tested on a battery of theory of mind tasks at two levels of difficulty (first- and second-order theory of mind), and grouped according to their performance (Happe, 1993). Five subjects who failed all the theory of mind tasks, 5 subjects who passed all and only first-order tasks, and 6 subjects who passed both first- and second-order theory of mind tasks were compared with 14 7- to 8-year-olds. The autism group was of mean age 18 years, and had a mean IQ of around 80. The three autism groups and the control group obtained the same score for total number of words correctly read. As predicted, however, the young normal subjects, but not the subjects with autism, were sensitive to the relative position of target homograph and disambiguating context; "There was a big tear in her eye", versus "In her dress there was a big tear". The normal controls showed a significant advantage when sentence context occurred before (rare pronunciation) target words (scoring 5 out of 5, versus 2 out of 5 where target came first), while the subjects with autism (as in Frith & Snowling, 1983) tended to give the more frequent pronunciation regardless (3 out of 5 appropriate pronunciations in each case). The important point of this study was that this was true of all three autism groups, irrespective of level of theory of mind performance. Even those subjects who consistently passed all the theory of mind tasks (mean VIQ 90) failed to use sentence context to disambiguate homograph pronunciation. It is possible, therefore, to think of weak central coherence as characteristic of even those subjects with autism who possess some mentalising ability.
Happe (1994c) explored this idea further by looking at WISC-R and WAIS subtest profiles. Thirty children and adults with autism who failed standard first-order false belief tasks were compared with 21 subjects who passed. In both groups Block Design was a relative peak in non-verbal performance for the majority of subjects; 86% of "passers", and 85% of "failers". In contrast, performance on the Comprehension subtest (commonly thought of as requiring pragmatic and social skill) was a low point in verbal performance for 76% of "failers" but only 30% of "passers". It seems, then, that while social reasoning difficulties (as shown by Wechsler tests) are striking only in those subjects who fail theory of mind tasks, skill on nonverbal tasks benefiting from weak central coherence is characteristic of both passers and failers.
There is, then, preliminary evidence to suggest that the central coherence hypothesis is a good candidate for explaining the persisting handicaps of the talented minority. So, for example, when theory of mind tasks were embedded in slightly more naturalistic tasks, involving extracting information from a story context, even subjects with autism who passed standard second-order false belief tasks showed characteristic and striking errors of mental state attribution (Happe, 1994b). It may be that a theory of mind mechanism which is not fed by rich and integrated contextual information is of little use in everyday life (Happe, 1994d).
The finding that weak central coherence may characterize people with autism at all levels of theory of mind ability, goes against Frith's (1989) original suggestion that a weakness in central coherence could by itself account for theory of mind impairment. At present, all the evidence suggests that we should retain the idea of a modular and specific mentalising deficit in our causal explanation of the triad of impairments in autism. It is still our belief that nothing captures the essence of autism so precisely as the idea of "mind-blindness". Nevertheless, for a full understanding of autism in all its forms, this explanation alone will not suffice. Therefore, our present conception is that there may be two rather different cognitive characteristics that underlie autism. Following Leslie (1987, 1988) we hold that the mentalising deficit can be usefully conceptualised as the impairment of a single modular system. This system has a neurological basis - which may be damaged leaving other functions intact (eg. normal IQ). The ability to mentalise would appear to be of such evolutionary value (Byrne & Whiten, 1988; Whiten, 1991) that only insult to the brain can produce deficits in this area. By contrast, the processing characteristic of weak central coherence, as illustrated above, gives both advantages and disadvantages, as would strong central coherence. It is possible, then, to think of this balance (between preference for parts versus wholes) as akin to a cognitive style, which may vary in the normal population. No doubt, this style would be subject to environmental influences, but, in addition, it may have a genetic component. It may be interesting, then, to focus on the strengths and weaknesses of information processing in autism, in terms of weak central coherence, in looking for an extended phenotype for autism.
With the speculative link to cognitive style rather than cognitive deficit, the central coherence hypothesis differs radically not only from the theory of mind account, but also from other recent theories of autism. In fact, every other current psychological theory claims that some significant and objectively-harmful deficit is primary in autism. Perhaps the most influential of such general theories is the idea that people with autism have executive function deficits, which in turn cause social and non-social abnormalities. The umbrella term "executive functions" covers a multitude of higher cognitive functions, and so is likely to overlap to some degree with conceptions of both central coherence and theory of mind. However, the hypothesis that people with autism have relatively weak central coherence makes specific and distinct predictions even within the area of executive function. For example, the "inhibition of prepotent but incorrect responses" may contain two separable elements: inhibition and recognition of context-appropriate response. One factor which can make a prepotent response incorrect is a change of context. If a stimulus is treated in the same way regardless of context, this may look like a failure of inhibition. However, people with autism may have no problem in inhibiting action where context is irrelevant. Of course it may be that some people with autism do have an additional impairment in inhibitory control, just as some have peripheral perceptual handicaps or specific language problems.
The central coherence account of autism is clearly still tentative and suffers from a certain degree of over-extension. It is not clear where the limits of this theory should be drawn - it is perhaps in danger of trying to take on the whole problem of Meaning! One of the areas for future definition will be the level at which coherence is weak in autism. While Block Design and Embedded Figures tests appear to tap processing characteristics at a fairly low or perceptual level, work on memory and verbal comprehension suggests higher level coherence deficits. Coherence can be seen at many levels in normal subjects, from the global precedence effect in perception of hierarchical figures (Navon, 1977) to the synthesis of large amounts of information and extraction of inferences in narrative processing (eg. Trabasso & Suh, 1993). One interesting way forward may be to contrast local coherence within modular systems, and global coherence across these systems in central processing. So, for example, the calendrical calculating skills of some people with autism clearly show that information within a restricted domain can be integrated and processed together (O'Connor & Hermelin, 1984; Hermelin & O'Connor, 1986), but the failure of many such savants to apply their numerical skills more widely (some cannot multiply two given numbers) suggests a modular system specialized for a very narrow cognitive task. Similarly, Norris (1990) found that building a connectionist model of an "idiot savant date calculator" only succeeded when forced to take a modular approach.
Level of coherence may be relative. So, for example, within text there is the word to word effect of local association, the effect of sentence context, and the larger effect of story structure. These three levels may be dissociable, and it may be that people with autism process the most local of the levels available in open-ended tasks. The importance of testing central coherence with open-ended tasks is suggested by a number of findings. For example, Snowling & Frith (1986) demonstrated that it was possible to train subjects with autism to give the context appropriate (but less frequent) pronunciation of ambiguous homophones. Weeks and Hobson (1987) found that subjects with autism sorted photographs of faces by type of hat when given a free choice, but, when asked again, were able to sort by facial expression. It seems likely, then, that autistic weak central coherence is most clearly shown in (non-conscious) processing preference, which may reflect the relative cost of two types of processing (relatively global and meaningful versus relatively local and piece-meal).
Just as the idea of a deficit in theory of mind has taken several years and considerable (and continuing) work to be empirically established, so the idea of a weakness in central coherence will require a systematic programme of research. Like the theory of mind account, it is to be hoped that, whether right or wrong, the central coherence theory will form a useful framework for thinking about autism in the future.
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