16693
The Neural Correlates of Perceptual Closure in Adults and Elderly with Autism
Perceptual closure refers to the ability to form a global and coherent perceptual representation on the basis of few details. A classical example is provided by two-tone (black and white) images of human faces (Mooney faces). In a Mooney image, the local features become too ambiguous to be recognized individually, and must be disambiguated based on their context within a global configuration. Mooney faces have been used to investigate various aspects of intact and impaired face processing. Given that autism is typically associated with a detail-oriented visual processing style, the neural mechanisms underlying perceptual closure may be different in patients with autism spectrum disorders (ASD).
Objectives:
Examine the neural mechanisms underlying perceptual closure in adults and elderly with ASD.
Methods:
Using 3T event-related fMRI we measured BOLD-signal changes in 27 patients with ASD (31-76yrs) to investigate how the brain forms perceptual decisions about complex visual forms. One hundred upright faces and 100 visually similar non-face images were shown for 200ms in a random sequence. To identify closure-related activity contrasts of correctly identified faces minus non-faces were computed. Post-scanning tests included a self-paced shortened version of the same perceptual closure task to examine the overall ability to recognize face stimuli. To assess global-local interference processing, a Navon hierarchical figures test (large “global” letters composed of smaller “local” letters) was administered.
Results:
Behavior
Preliminary data suggest that participants with ASD show significant reduced detection rates (M=65% vs 92%; p<.001), but not reaction times (p>.1) during the perception of Mooney faces compared to non-faces. Performance inside the scanner and the self-paced task outside the scanner was significantly different, such that performance on the self-paced task showed higher hit-rates for faces (M=79%; p<.01) and non-faces (M=96%; p<.01). Reaction time differed between faces and non-faces (1.6s vs 2.2s; p=.014). The average local-global precedence score (LGP; local RT- global RT) was 41.4ms (SD=199.2ms) suggesting that, overall, there was no significant local or global precedence effect for the group (i.e. LGP was not significantly different from zero; t=1.8, d.f.=26, p=.29). No significant associations were found between measures of the Navon task and the perceptual closure task performance.
fMRI
The fMRI data showed increased activation for faces relative to non-faces in the right fusiform face area (FFA), bilateral inferior frontal gyri, bilateral parietal lobule, left amygdala and right angular gyrus and insula (FDR corrected: p<.05; >10 contiguous voxels). No age-related effects were found for behavioral and neuroimaging data.
Conclusions:
The behavioral data suggest that face recognition is more dependent on holistic processing than non-face recognition or global-local interference processing. This finding is further strengthened by the large difference in detection rates in the self-paced task. The fMRI data showed typical responses in the FFA and inferior frontal gyri consistent with other recent studies demonstrating increased activation for faces compared to non-faces in autism. Overall, these findings suggest a specific face recognition deficit in adults and elderly with ASD independent of age. While informative, future analyses will include a matched healthy control group to elucidate whether these results are specific for ASD.