Cognitive processing of global and local visual stimuli in autism spectrum disorder
MetadataShow full item record
An ongoing debate is whether people with autism spectrum disorder (ASD) have a local processing bias and to what extent impaired contextual processing is associated with this bias. The set of experiments employed in this project examined global and local processing, shifts between global and local processing, and low- and high-level visual processing in an attempt to address this issue. This thesis tested the hypotheses that (1) a local processing bias is associated with impaired global processing in ASD individuals, and (2) atypical processing style is linked with ASD severity. Twenty ASD individuals and 20 IQ and age (15-30 years) matched normal controls were administered a novel embedded figures task (local processing advantageous), a novel form matching task and novel shape integration task (global processing advantageous), a local-global switching task (which assessed attention broadening and attention narrowing ability), and a local and global motion detection task. The Social Responsiveness Scale was used to assess ASD severity. The ASD group correctly detected significantly more embedded shapes than controls. Compared to controls, ASD participants were disproportionately slower on the shape integration task relative to the form perception task. No overall group differences were found in attention broadening or attention narrowing ability. In addition, no group differences were found in local or global motion perception. Results also revealed a significant correlation between ASD severity and (1) faster response time on the embedded figures test, (2) slower response time on the shape integration task, (3) reduced attention broadening ability, and (4) reduced global motion perception. These findings confirm previous reports of enhanced local visual processing in ASD, and suggest that while global form perception is intact in ASD, global integration is more problematic. There was no evidence of generalized attentional impairments or motion perception abnormalities in ASD participants, suggesting that lower-level perceptual functions may be spared in people with ASD. Perhaps most intriguing was the observed association between ASD severity and enhanced local perception and impaired global processing. This association suggests that both a local processing bias and impaired global processing may play a role in the behavioral aspects of ASD symptomatology.