Blur-modulated orientation perception in the rod-and-frame task

In order to assess the role of blur in a rod-and-frame task, an afocal blurring technique was developed that restricted the blur to the frame. Three levels of blur were investigated, along with a nonblurred, directly viewed frame. Results showed a significant drop in the rod-and-frame effect (RFE) with increasing blur (decreasing spatial frequency), but spatial frequencies even as low as .092 cpd failed to reduce the RFE to zero. Decreasing luminance was correlated with increased blur, but control studies showed that variation in luminance levels between .007 and .0015 cd m^?2 had no effect on RFE. The finding of a spatial frequency dependency in the rod-and-frame task permits the development of a neuropsychological theory of individual and gender differences typically found in studies of static spatial orientation.