The influence of magnocellular and parvocellular visual information on global processing in White and Asian populations.

Humans have the remarkable ability to efficiently group elements of a scene together to form a global whole. However, cross-cultural comparisons show that East Asian individuals process scenes more globally than White individuals. This experiment presents new insights into global processing, revealing the relative contributions of two types of visual cells in mediating global and local visual processing in these two groups. Participants completed the Navon hierarchical letters task under divided-attention conditions, indicating whether a target letter "H" was present in the stimuli. Stimuli were either 'unbiased', displayed as black letters on a grey screen, or biased to predominantly process low spatial frequency information using psychophysical thresholds that converted unbiased stimuli into achromatic magnocellular-biased stimuli and red-green isoluminant parvocellular-biased stimuli. White participants processed stimuli more globally than Asian participants when low spatial frequency information was conveyed via the parvocellular pathway, while Asian participants showed a global processing advantage when low spatial frequency information was conveyed via the magnocellular pathway, and to a lesser extent through the parvocellular pathway. These findings suggest that the means by which a global processing bias is achieved depends on the subcortical pathway through which visual information is transmitted, and provides a deeper understanding of the relationship between global/local processing, subcortical pathways and spatial frequencies

Looking without Perceiving: Impaired Preattentive Perceptual Grouping in Autism Spectrum Disorder.

Before becoming aware of a visual scene, our perceptual system has organized and selected elements in our environment to which attention should be allocated. Part of this process involves grouping perceptual features into a global whole. Individuals with autism spectrum disorders (ASD) rely on a more local processing strategy, which may be driven by difficulties perceptually grouping stimuli. We tested this notion using a line discrimination task in which two horizontal lines were superimposed on a background of black and white dots organized so that, on occasion, the dots induced the Ponzo illusion if perceptually grouped together. Results showed that even though neither group was aware of the illusion, the ASD group was significantly less likely than typically developing group to make perceptual judgments influenced by the illusion, revealing difficulties in preattentive grouping of visual stimuli. This may explain why individuals with ASD rely on local processing strategies, and offers new insight into the mechanism driving perceptual grouping in the typically developing human brain

Stimulus Backgrounds and Time Course of Trial Events.

<p>Stimulus Backgrounds and Time Course of Trial Events.</p

Results of the Perceptual Grouping Task.

<p>Figures show the percentage of “correct" line judgments made in the illusion trials (a), the percentage of participants who reported having seen a pattern in response to the direct query (b), the percentage of participants who answered the forced-choice question correctly (c), and the mean confidence ratings of the response given to the forced-choice question (d). Error bars represent 95% confidence intervals.</p

Individual results of the Perceptual Grouping Task for the ASD group.

<p>Lines represent the 95% confidence interval of the typically developing group.</p

Schematic diagram showing the experimental structure.

<p>Schematic diagram showing the experimental structure.</p