The present study aims to acquire insight into the WAIS III profiles of normal intelligent adults with HFA and Asperger syndrome. Profiles in the total group and differences between the two diagnostic groups will be examined.

All participants were recruited from the GGZ (Mental Health Center) Eindhoven and Oost-Brabant. The participants met the criteria for Asperger syndrome or HFA. Participants with relevant neurodevelopmental conditions and genetic conditions were excluded, as were institutionalized patients and patients with a Full Scale IQ below 80.

The mean Full Scale IQ of the participants was 110.16, individual scores varied between 83 and 145 (see Table?1).

All individuals ranged in age from 18 to 60?years. The mean age was 41.93. Of all participants, 25 finished higher education and 30 individuals had work. 23 participants lived together with a partner. The relatively large number of participants who had a relationship, worked and were well educated emphasizes the relatively high level of functioning in this group.

Hetero-anamnestic information was gathered using the Dutch version of the Autistic Disorder Diagnostic Interview, revised version (ADI-R, Lord et?al. ¹⁹⁹⁴), administered by psychologists who were officially trained in the administration and scoring of the instrument. To gather anamnestic information, a semi-structured interview was used to assess presence of the DSM-IV criteria of HFA and Asperger syndrome (APA ¹⁹⁹⁴). Because of the controversial nature of the DSM-IV criteria (Ghaziuddin et?al. ¹⁹⁹²; Mayes et?al. ²⁰⁰¹), additional questions were used to differentiate between HFA and Asperger syndrome, based on the diagnostic criteria of Gillberg and Gillberg (¹⁹⁸⁹) and ICD-10 (WHO ¹⁹⁹³).

The intelligence profile was assessed using the Dutch translation of the WAIS III (Wechsler ¹⁹⁹⁷). The WAIS-III has excellent psychometric properties (Sattler and Ryan ¹⁹⁹⁹) and has been validated for the Dutch population (Wechsler ¹⁹⁹⁷).

Differences between VIQ and PIQ for all participants and both diagnostic groups were analyzed by means of paired t-tests. No statistically significant effects were found for any of the investigated groups (see Table?2).

Factor Scale profiles were studied within the total group and between the two diagnostic subgroups by means of repeated measures analysis of variance. Mauchly?s test indicated that the assumption of sphericity was not met. Therefore the degrees of freedom were corrected using the Huynh?Feldt correction (??=?.89). Post-hoc comparisons using the Sidak adjustment for multiple comparisons showed that the main effect of the WAIS III Factor Scale was statistically significant (F(2.7,109.7)?=?7.0, p?<?0.001). An interaction effect of differences in Factor Scale mean by diagnostic group was also found (F(2.7, 109.7)?=?2.7, p?=?0.05). To find out which differences in WAIS III Factor Scale means added to the significant main effect, post hoc pairwise comparisons were done. This showed that the main effect in the total group can be attributed to Processing Speed being significantly lower than Verbal Comprehension (p?<?.01) and Perceptual Organization (p?<?.005).

Post hoc pairwise comparisons were done for the two diagnostic groups to analyse the ?within group? effect. In the Asperger group, no significant differences in Factor Scale mean scores were found. The HFA group however, showed a significant lower Processing Speed compared to Verbal Comprehension (p?<?.01), Perceptual Organization (p?<?.01) and Freedom from Distractibility (p?<?.05) (see Table?3).

The Subtest profiles were explored within the total group and between the two diagnostic subgroups by means of a repeated measures analysis of variance. The assumption of sphericity was not met. Therefore the degrees of freedom were corrected using the Huynh?Feldt correction (??=?.82). Post-hoc comparisons were performed using the Sidak adjustment for multiple comparisons. The results (see Table?4) showed a significant main effect of the type of Subtest (F(10.7,438.7)?=?4.8, p?<?0.001).

An interaction effect of Subtest by diagnosis was also found (F(10.7, 438.7)?=?2.1, p?<?0.05), indicating that the patterning of the WAIS III subtest mean scores for the two diagnostic groups differs. Table?5 and 6 show the mean Subtest scores and standard deviations for the HFA group and the Asperger syndrome group.

Post hoc pair wise comparisons showed that the main effect in the total group can be attributed to the fact that Digit-Symbol Coding was significantly lower than Vocabulary (p?<?.05), Arithmetic (p?<?.05), Information (p?<?.005), Comprehension (p?<?.005), Block Design (p?<?.05) and Matrix Reasoning (p?<?.005). Furthermore, Symbol Search was lower than Information (p?<?.05) and Comprehension (p?<?.05).

Post hoc pair-wise comparisons were also performed for the two diagnostic groups to analyze the ?within group? effect. The two groups showed significant differences in Subtest scores. In the Asperger syndrome group, Digit Span was lower than Comprehension (p?=?.005) and Block Design (p?<?.05).

In the HFA group performance was significantly higher in Information compared to Digit-symbol Coding (p?<?.05) and Symbol Search (p?<?.05). Furthermore, Digit-Symbol Coding was lower than Matrix Reasoning (p?<?.05).

No significant differences were found between VIQ and PIQ in the total group nor in the two diagnostic subgroups. The results are in line with factor analytic studies showing that the VIQ-PIQ dichotomy is not valid for general populations (Arnau and Thompson ²⁰⁰⁰; Taub ²⁰⁰¹).

The Asperger syndrome group was characterized by a flat Factor Scale profile in the Asperger syndrome group, while the HFA group performed significant low in Processing Speed. A low Processing Speed indicates problems in speed of processing visual information (Wechsler ¹⁹⁹⁷). Adults with HFA apparently need more time than other people to process and integrate visual information and to act on this information.

The Processing Speed performance of the HFA group might be influenced by problems with top-down processing and ignoring irrelevant details, which are characteristic of people with HFA (Happ? ²⁰⁰⁵; Shah and Frith ¹⁹⁹³). In order to maintain an overview of what they are doing, they work slowly.

Analyses showed different Subtest patterns in the HFA and the Asperger syndrome groups. The HFA group performed significantly low in Digit-Symbol Coding and Symbol Search. These two subtests together form the Processing Speed Factor. The low scores for these subtests represent the problems in speed of processing visual information as described in the preceding paragraph.

The HFA group showed significantly high performance in Information and Matrix Reasoning. High scores for Information are in line with the fact that people with autism usually acquire much factual knowledge (Happ? ¹⁹⁹⁹).

Matrix Reasoning taps nonverbal perceptual reasoning. Matrix Reasoning is the only Perceptual Organization subtest without a time limit and is possibly not influenced by low Processing Speed performance scores. The good performance of the HFA group can probably be attributed to their visual-spatial strengths (Lincoln et?al. ¹⁹⁹⁵; Tsatsanis ²⁰⁰⁵) and to the absence of a time limit for this subtest.

In the Asperger group, scores for Digit Span were relatively low. Digit Span taps working memory capabilities (Wechsler ¹⁹⁹⁷), which can been defined as ?the ability to hold in mind past states of the environment and past actions while currently performing an action? (Russell ¹⁹⁹⁷). People with autism or Asperger syndrome tend to store information in details instead of using strategies, which often leads to problems in retaining information (Happ? ²⁰⁰⁵; Minshew et?al. ¹⁹⁹²; Tsatsanis ²⁰⁰⁵). Low Digit Span scores in the Asperger group may reflect problems in applying strategies to retain information.

The Asperger syndrome group performed significantly well on Comprehension. High scores on Comprehension in this group seem to contradict former research results (Klin et?al. ²⁰⁰⁵; Mayes and Calhoun ²⁰⁰³; Siegel et?al. ¹⁹⁹⁶). However, people with Asperger syndrome often try to function in society by analyzing social situations at a cognitive level, which has been described as using an ?explicit theory of mind? (Frith and Happ? ¹⁹⁹⁹). A extremely well developed explicit theory of mind may have caused the Asperger syndrome group to have such high scores on Comprehension.

The Asperger Syndrome group also performed significantly well on Block Design. Strengths in Block Design have often been reported in studies of people with HFA or Asperger syndrome (Happ? ²⁰⁰⁵; Shah and Frith ¹⁹⁹³). This has been attributed to strengths in processing unconnected stimuli outside a meaningful context, which go together with the central coherence problems seen in people with autistic impairment (Shah and Frith ¹⁹⁹³).

*p?< .05.

*p?< .05.

*p?< .05.

*p?< .05.