Children with Autism Show Perceptual Bias Consistent with Altered Ventral Visual Pathway Processing

Background: Previous studies have demonstrated a visual perceptual bias in autism that results in a focus on details, or ‘local’ features, often at the expense of the whole, or ‘global’ features. This pattern is opposite to that usually observed in typically developing populations. It is possible that this bias reflects changes along the ventral visual pathway, which assembles local image features into representations of whole shapes.

Objectives: We asked whether children with high-functioning autism (HFA) are more perceptually sensitive to local rather than global geometric features known to be explicitly represented in ventral pathway visual areas (e.g., areas V4, IT).  If so, this would suggest altered processing in regions responsible for assembling object parts into whole shapes.

Methods: We studied children with and without HFA on a two-alternative forced choice task that asked which shape was most different from a sample shape.  We generated shapes using Bezier splines and locally or globally manipulated parameters (curvature, orientation, relative position) that neurophysiological studies have shown to be explicitly represented in higher-level ventral visual cortex. An algorithm was developed to quantitatively compare differences between shapes on local and global scales.

Results: First, we confirmed that our algorithm quantitatively discerns local and global manipulations of the abstract shape stimuli.  Second, our preliminary data show that children with HFA select local manipulations as having a greater effect on altering shape than global manipulations.

Conclusions: We have quantitatively manipulated local and global geometric characteristics that are explicitly represented in higher-level ventral visual cortex. Relative to controls, children with HFA perceive local geometric differences to be more salient than global differences, implying altered processing in the ventral visual pathway. This study provides an objective measure of the local visual bias in autism and establishes a link between this bias and the neural basis of object perception.