The current study is the first to examine whether high-functioning individuals with autism can form a mean prototype of facial information. Overall, the control group chose the mean prototype more often than the autism group, suggesting a difference in prototype formation abilities for the autism group. When the sample was split into children and adults, the pattern suggested that the effects might be driven more by the older study participants, but confirmation of this moderating variable awaits further study. The marginally significant results in the child group reflect a continuing development of the processing abilities that are needed to discriminate subtle spatial variation in typically developing children.
These results add to those of Klinger and colleagues, suggesting that individuals with autism have difficulty forming mean prototypes. Whereas some previous studies used stimuli where it was not necessary to form the mean prototype in order to succeed (e.g., Molesworth, et al.), the current study provided a more stringent test of mean prototype formation for several reasons. First, the current study used faces, a natural category exhibiting subtle featural variations that are quantitative in nature. Second, stimuli were designed using subtle variations of continuous facial attributes that were combined to ensure participants saw mean prototype values less frequently than mode prototype values. Thus, pure memorization of features would result in individuals choosing the mode prototype more often, whereas abstracting average features would result in choosing the mean prototype more often.
The current study suggests that individuals with autism don't automatically abstract prototypical information during an exposure paradigm with passive face viewing. Still at issue is whether individuals with autism can form mode prototypes. Molesworth and colleagues have found that individuals with autism can form a mode prototype, but our study did not replicate this finding (i.e., the autism group did not choose the mode prototype more than the mean prototype). One possible explanation for the difference in results is the amount of subtlety in the features that were varied. It is possible that when the varied features are more obvious or qualitative in nature, individuals with autism can abstract this information. Klinger & Dawson’s (2001)
finding that individuals with autism could form a prototype when there was an obvious rule for category membership supports this notion.
Still, an important question is why individuals with autism have difficulty forming mean prototypes, something even infants do successfully. To form a mean prototype, one must attend to different objects in the world, encode how features vary, learn the boundaries of featural variation, and store a mental average of these variations for each object category. For faces in particular, one needs to be able to encode the variations of spatial or configural features. Prior research on face recognition abilities of individuals with autism has shown that they have difficulty processing configural/spatial information and instead attend to non-configural/non-spatial information such as features and details (e.g., Sasson, 2006
). Individuals with autism may not attend to the variation of spatial features of faces/objects unless the variation is obvious. For example, typically developing individuals learn that noses range from very wide to very narrow, with all sizes in between, but individuals with autism may only notice that noses are either wide or narrow. If this is the case, individuals with autism would have difficulty abstracting an accurate average. Attention to non-configural information could also negatively affect mean prototype formation. That is, because of an enhanced attention to non-configural details, they may process categories more dichotomously (as big/small or wide/narrow). Hence their attention to details may hinder the detection of variations that occur within continuously varying features (such as nose width), and they may only learn that noses are wide or narrow (dichotomous).
In summary, the current results provide further evidence that individuals with autism have difficulty forming prototypes, and more specifically mean prototypes of facial information. It is possible that the results may reflect chance behavior; however, the control group showed clear evidence of selecting the mean prototype at levels greater than chance. It may also be argued that the results of the autism group were not due to a difference in mean prototype formation but rather a general face perception deficit from reduced attention to faces resulting in less experience with faces. Since infants have minimal experience with faces and can abstract mean prototypes, this possibility is less likely but cannot be ruled out. To determine how early mean prototype formation deficits are present in individuals with autism; future research should replicate these results and extend studies to younger populations. Future research should also be aimed at the nature of the prototype that is abstracted by individuals with autism (e.g. mean vs. mode) and the extent to which varied dimensions (e.g. subtle continuous vs. obvious discrete) affect the type of prototype formed.