Blur clarified: a review and synthesis of blur discrimination

Blur is an important attribute of human spatial vision, and sensitivity to blur has been the subject of considerable experimental research and theoretical modeling. Often, these models have invoked specialized concepts or mechanisms, such as intrinsic blur, multiple spatial frequency channels, or blur estimation units. In this paper, we review the several experimental studies of blur discrimination and find that they are in broad empirical agreement. However, contrary to previous modeling efforts, we find that specialized mechanisms are not required and that the essential features of blur discrimination are fully accounted for by a visible contrast energy (ViCE) model, in which two spatial patterns are distinguished when the integrated difference between their masked local visible contrast energy responses reaches a threshold value. In the ViCE model, intrinsic blur is represented by the high-frequency limb of the contrast sensitivity function, but the low-frequency limb also contributes to the predictions for large reference blurs, and the model includes masking, which improves predictions for high-contrast stimuli.