High- Vs. Low-Level Perceptual Processing in Autism: An fMRI Study

Background:

Behavioral evidence suggests that low-level visual-spatial processing may be preserved or enhanced in autism. On the other hand, the capacity of individuals with autism to process high-level complex stimuli like faces is impaired. Theories have been proposed to interpret the discrepancy in performance in autism between low-level and high-level complex visual perceptual tasks. Investigation of the brain mechanisms, including brain activation as well as functional and anatomical connectivity underlying this discrepancy may lead to further understanding of the cognitive processing associated with the behavioral disorder of autism.

Objectives:

This fMRI study compares the behavioral performance, brain activation, and cortical synchronization in individuals with autism and healthy controls when they perform a low-level line counting task and a high-level possibility judgment of 3-D figures.

Methods:

In the experiment, participants with high-functioning autism (HFA) and age/IQ-matched healthy controls see possible and impossible 3-D figures. In the possibility judgment condition, participants are presented with a single figure to be judged as possible or impossible to be constructed in three dimensions; in the line counting condition, red and green lines are drawn on a possible or impossible figure and participants are asked to count and decide whether there are more red or green lines. To date, data have been collected on 8 adults with HFAs and 14 typically developing age and ability-matched controls. Data collection is on-going.

Results:

It is anticipated that the behavioral performance of the individuals with autism on the possibility judgment task will be worse (e.g., slower reaction times and lower accuracy), and that they will show lower functional connectivity between frontal regions and more posterior regions than healthy controls. On the other hand, their cognitive ability in the line counting task will be preserved or enhanced. The autism group may show normal or even enhanced functional connectivity among posterior regions associated with perceptual processing. The behavioral performance on the collected individuals is consistent with the expected pattern. The fMRI data analysis is on-going.

Conclusions:

If the results are as expected, it will suggest that high-level complex perceptual tasks may require the coordinated functioning of the frontal-posterior system, which is underconnected in the autism. Instead low-level perceptual tasks that do not demand a lot of frontal input are preserved in autism.