During typical development, specialized processing biases for faces emerge that are not observed for other visual stimuli. For example, faces are processed configurally (Maurer et al. 2002), which includes synthesizing the whole face rather than its isolated features (i.e., holistic processing), sensitivity to overall orientation of one feature to another (i.e., first-order relations) and knowledge of distances between features (i.e., second-order relations) (e.g., Tanaka and Farah 1993; Tanaka and Sengco 1997; Young et al. 1987). Viewing faces in an inverted orientation is more disruptive to recognition than the inversion of non-face stimuli (e.g., Yin 1969), probably because inversion disrupts configural processing (e.g., Diamond and Carey 1986; Young et al. 1987).

Impaired configural processing in autism has been indirectly supported by a weakened face inversion effect (Hobson et al. 1988; Langdell 1978; Rose et al. 2007; Teunisse and de Gelder 2003; but see Lahaie et al. 2006). Further, individuals with ASD are less impacted than controls when configural information is disrupted by a split face paradigm with stimulus detection after a brief delay (Teunisse and de Gelder 2003). Individuals with autism are also more reliant on individual facial features (Hobson et al. 1988) and on high spatial frequency information, which emphasizes local details over global configuration (Deruelle et al. 2004). Finally, based on a priming task it has been suggested that individuals with ASD have enhanced featural processing with preserved configural processing (Lahaie et al. 2006).

Despite the mounting evidence of unusual biases in configural processing by individuals with autism, there have been fewer direct measures of sensitivity to second-order relations or to the holistic processing advantage. The Thatcher illusion, thought to disrupt second-order relations, was detected as accurately by lower functioning children with ASD as controls (Rouse et al. 2004). In direct comparisons of holistic versus featural processing, high-functioning children with ASD performed similarly to controls across whole face and feature conditions (Lopez et al. 2008). Two research groups found evidence of holistic processing by high-functioning children and teens with ASD in a match to sample task with a short memory delay, but only under conditions of attentional cuing (Lopez et al. 2004) or when recognition relied on information contained in the mouth region (Joseph and Tanaka 2003). Holistic processing was not found in the absence of cues or when recognition relied on the eyes, respectively. An attentional bias toward the bottom part of faces by individuals with ASD has been suggested (Joseph and Tanaka 2003; Klin et al. 2002), but this finding has not been consistently demonstrated (e.g., Bar-Haim et al. 2006; Lahaie et al. 2006).

The goal of the current study is to extend the literature by directly measuring the accuracy and speed of these two sub-domains of configural processing in a group of adult participants. Most investigations have tested accuracy in developmental samples. By testing high-functioning adults with ASD, we aim to tap face processing abilities independent of cognitive confounds and with less risk of potential differences resulting from dissimilar rates of development. Experiment 1 tests for a recognition advantage when features are presented in the context of a whole face rather than alone (Joseph and Tanaka 2003; Tanaka and Farah 1993). Featural processors would perform similarly across conditions. The reduced holistic advantage with high-functioning adolescents (Lopez et al. 2004) supports the hypothesis that adults with ASD would exhibit a pattern of reduced holistic processing compared with controls. The facial inversion effect and attention to the top versus bottom of the face are also measured. Mixed findings of selective attention to the lower portion of the face have been reported, but we anticipate a processing advantage for the mouth region on the basis of findings by Joseph and Tanaka (2003). Experiment 2, adapted from Freire and Lee (2001), directly measures sensitivity to second-order relations by measuring the ability to detect manipulations of the distances between features. The direct manipulation of second-order relations used here is novel with this population, but previous findings with the Thatcher effect (Rouse et al. 2004) suggest this sub-domain may be spared.

Two interactions were of interest when reaction time was examined. First, the group with ASD responded more quickly when mouths were tested, while the controls were more rapid in the eye condition. This is seemingly in contrast to an advantage with accuracy in the whole-eye condition. We speculate that adult participants with ASD may be more efficient with recognition of the mouth region due to evidence of early attentional bias for this region with children, but with experience and direct intervention with social skills, they may have learned to redirect their attention to the top of the face as a (less automatic) compensatory strategy. Second, the difference in reaction time for upright versus inverted faces was twice as large for controls compared with the group with ASD. This finding is consistent with other evidence of a weakened inversion effect in ASD.

Experiment 2 also revealed reduced accuracy across conditions by the group with ASD, even when covarying general (non-face) memory ability and accounting for possible response bias. Accuracy significantly differed depending on the magnitude of the change made to second order relations of test faces for both groups. This finding is consistent with findings by Rouse et al. (2004) who demonstrated lower functioning children with ASD were sensitive to manipulations of second-order relations. However, the group with ASD differed from controls in its pattern of response speed across conditions, even with memory as a covariate. While controls quickly recognized large manipulations, relative to small or no change conditions, response times were similar across these conditions for the group with ASD. Taken together, this finding suggests that while individuals with ASD can detect large changes to configural information, they are slower to do so. Last, a relation between communication impairments and accuracy emerged. We suspect that participants with ASD who struggled with flexible use of language may have been overly literal in interpreting instructions to decide whether faces were “exact matches.”

Important limitations must be mentioned. First, there were significant group differences on standardized measures of face and object memory. Face memory was significantly related to overall accuracy for both experiments; this suggests that both face processing abilities and generalized memory ability may contribute to performance. In order to address this possibility, analyses were conducted with object memory as a covariate; group differences in overall accuracy as well as differences in the within group patterns of performance remained for both tasks. Second, because the aim of the current study was to test the specific aspects of configural processing that are argued to be unique to faces, we did not include an object condition in our experimental tasks. Examining configural processing for objects would be useful in addressing generalized cognitive differences that may contribute to performance. However, evidence for face specific impairment rather than more generalized cognitive impairments (i.e., processing speed, attention, memory, central coherence) in ASD is taken from a lack of group differences in overall reaction time between groups and significant within group differences on both tasks. A third limitation is lack of masking in Experiment 2. This may have allowed participants to overlay a mental image of the target onto the test image, a strategy that may have benefitted the control group. Lastly, this as well as the majority of face processing investigations has used unfamiliar faces, and recent work suggests processing may be less disrupted with familiar faces (e.g., Wilson et al. 2007).