Local Visual Processing in High Obsessive Compulsive Disorder (OCD) Scorers.

Reaction times for big and small letters (global and local levels) were compared and examined to see whether differences would occur between a low scoring and high scoring Obsessive-  Compulsive Disorder (OCD) group. OCD patients have been shown to notice and pay more attention to small details (local bias) compared to most other populations (Shapiro, 1965; Yovel et al. 2006; Caberea et al., 2001). Although there is research supporting a local bias in OCD patients, it is unclear whether the bias occurs in the early stages of visual processing or in a later memory stage (Moritz & Wendt, 2006; Hermans et al, 2008). The study specifically examined a potential local bias for high OCD scorers in the early visual stage by manipulating perceptual and attentional mechanisms in two hierarchical letter tasks (Navon, 1977; Miller, 1981a, Plaisted et al. 1999). In Experiment 1, participants were told which level (the big or small letter) to respond to, results showed that high OCD scorers responded faster to local letters, showing support for a local processing advantage. Conversely, the low OCD group responded quicker to the global level. The finding of a local advantage in Experiment 1 suggests that the local advantage may be due to perceptual mechanisms as attention was already directed to the relevant level. However, in Experiment 2 where attention was not directed and the image quality was manipulated, local and global advantage effects were not replicated for the high and low OCD groups respectively. This showed that attentional and perceptual mechanisms did not make one level easier to process over the other. Therefore, it is possible that any local bias for OCD patients occurs in a later processing stage.