Enhanced Contrast Sensitivity Confirms Active Compensation in Blur Adaptation

Abstract

To determine the effects of defocus-induced blur adaptation on human contrast sensitivity (CS) function. Defocused (+2 D) CS was measured for spatial frequencies between 0.5 and 12 cycles per degree (cpd) before and after adaptation to +2 D blur in six subjects with normal vision. During the 30-minute adaptation period with +2 D lens, subjects were exposed to a succession of static calibrated natural images that were also used to "top-up" adaptation between postadaptation trials. After 30 minutes of blur adaptation, CS was found to be significantly reduced at 0.5 cpd (P = 0.023), though it was enhanced at 8 cpd (P = 0.007) and 12 cpd (P = 0.005). The average sensitivity reduction at 0.5 cpd was 0.20 log(10) units, whereas enhancements were 0.09 and 0.16 log(10) units at 8 and 12 cpd, respectively. The present study demonstrates a novel finding that 30 minutes of defocused viewing results in enhanced high spatial frequency CS. The concurrent observation of low spatial frequency CS reduction suggests that the changes are not caused by simple learning effects but are likely caused by neural adaptation.