Journal of the International Neuropsychological Society

Symposium

Functional brain organization for visual search in ASD

BRANDON KEEHNa1a2, LAURIE BRENNERa2, ERICA PALMERa2, ALAN J. LINCOLNa3 and RALPH-AXEL MÜLLERa2a4 c1

a1 Brain Development Imaging Laboratory, Department of Psychology, San Diego State University, San Diego, California

a2 Joint Doctoral Program in Language and Communicative Disorders, San Diego State University, San Diego, California, University of California, San Diego, San Diego, California

a3 Developmental Neuropsychology Laboratory, Alliant International University, San Diego, California

a4 Department of Cognitive Science, University of California, San Diego, San Diego, California

Abstract

Although previous studies have shown that individuals with autism spectrum disorder (ASD) excel at visual search, underlying neural mechanisms remain unknown. This study investigated the neurofunctional correlates of visual search in children with ASD and matched typically developing (TD) children, using an event-related functional magnetic resonance imaging design. We used a visual search paradigm, manipulating search difficulty by varying set size (6, 12, or 24 items), distractor composition (heterogeneous or homogeneous) and target presence to identify brain regions associated with efficient and inefficient search. While the ASD group did not evidence accelerated response time (RT) compared with the TD group, they did demonstrate increased search efficiency, as measured by RT by set size slopes. Activation patterns also showed differences between ASD group, which recruited a network including frontal, parietal, and occipital cortices, and the TD group, which showed less extensive activation mostly limited to occipito-temporal regions. Direct comparisons (for both homogeneous and heterogeneous search conditions) revealed greater activation in occipital and frontoparietal regions in ASD than in TD participants. These results suggest that search efficiency in ASD may be related to enhanced discrimination (reflected in occipital activation) and increased top-down modulation of visual attention (associated with frontoparietal activation). (JINS, 2008, 14, 990–1003.)

(Received December 11 2007)

(Revised July 22 2008)

(Accepted July 22 2008)

Correspondence:

c1 Correspondence and reprint requests to: Ralph-Axel Müller, Department of Psychology, San Diego State University, MC1863, 6363 Alvarado Ct. #225E, San Diego, CA. E-mail: amueller@sciences.sdsu.edu