Abstract
Perceptual learning (PL) can improve visual functions, including vision sharpness, in adults with poor vision due to abnormal development (amblyopia) or blurred input due to uncorrected refractive error (presbyopia, myopia). The ability of the brain to perform "de-blurring" of highly blurred images following PL is not fully understood. One hypothesis is that improved blur discrimination is the result of improved contrast discrimination. However, there may be separate mechanisms for blur and contrast discrimination (Morgan 2017), therefore improved contrast discrimination may not fully underlie improved and blur discrimination. This study explored the effect of PL on blur discrimination without contrast cues. The participants (n=9, median age 24) were corrected-to-normal or uncorrected myopes. Participants were asked to discriminate between two Gaussian blurred circles using a temporal 2IFC paradigm. One interval (the reference) had a constant blur standard deviation (6 arcmin) and the other (the test) interval had one of 11 different blur levels; 5 increments, 5 decrements and one equal to the reference. Contrast jitter was applied to both reference and test intervals to minimize any contrast cues. All blur levels were intermixed. Training sessions (6-8) lasting about 20 minutes, consisted of 40 trials per condition (total 440). Participants were pre- and post-tested on both higher and lower reference blur levels and on visual acuity. Blur discrimination thresholds improved in the trained eye and transferred to the untrained eye. The improved blur discrimination also transferred to both higher (8 arcmin) and lower (4.5 arcmin) reference blur levels, and visual acuity improved by, on average, 1.2 lines. Participants with uncorrected or not fully corrected myopia showed improvement in blur discrimination thresholds and improved visual acuity following blur training. Our results show that improved blur discrimination without contrast cues transferred to improved visual acuity, suggesting that PL can modify blur discrimination mechanisms directly.