Perceptual learning improves neural processing in myopic vision

Abstract

Visual performance is jointly determined by the quality of optical transmission of the eye and neural processing in the visual system. An open question is: Can effects of optical defects be compensated by perceptual learning in neural processing? To address this question, we conducted a perceptual learning study on 23 observers with myopic vision, targeting high frequency deficits by training them in a monocular grating detection task in the non-dominant eye near their individual cutoff spatial frequencies. The contrast sensitivity function and visual acuity in both eyes (without optical correction) were assessed for all the observers in the training group before and after training, and for all the observers in the control group twice with a 10-day interval between the tests. In addition, the threshold versus external noise contrast function was measured for five observers in the training group before and after training. We found that (a) training significantly improved contrast sensitivity at the trained spatial frequency, visual acuity, and contrast sensitivity over a wide range of spatial frequencies in both eyes; (b) training did not lead to any significant refractive changes; (c) the mechanism of improvements was a combination of internal additive noise reduction and external noise exclusion; and (d) the improvements in visual acuity and contrast sensitivity were almost fully retained for at least four months in the three observers tested. These results suggest that perceptual learning may provide a potential noninvasive procedure to compensate for optical defects in mild to modest myopia.

Perceptual Learning at Higher Trained Cutoff Spatial Frequencies Induces Larger Visual Improvements

“…Thus, our results may also suggest that the initial VA had a positive effect on visual improvement, which is opposite to previous studies. For example, Yan et al (2015) found greater acuity improvement for observers with worse initial VA. Yehezkel et al (2016) also found that subjects with more advanced presbyopia and thus poorer initial VA showed the greatest improvement in VA. Even so, there were at least two differences between these previous studies and this study.…”

“…First, the initial vision and age differed. Yan et al (2015) recruited myopic adult observers; Zhou et al (2012) recruited presbyopic adults; and the present study recruited adolescent observers with normal or close to normal vision. Second, the incentive conditions were different.…”

“…An individual customized training procedure based on subgroups contributes to maximizing the training effect. Several previous studies using a grating detection task trained observers near each individual's cutoff spatial frequency, which was defined as the spatial frequency at which the contrast threshold of the pretraining CS function (CSF) was a constant (Zhou et al, 2006(Zhou et al, , 2012Huang et al, 2008;Yan et al, 2015;Zhang et al, 2018); that is, each observer was trained at individual spatial frequencies. Thus, an interesting question is who gains the most from perceptual learning.…”

High reward enhances perceptual learning

“…PTM analysis of the CSFs in both the zero and high external-noise conditions (Chen et al, 2014 ; Yan et al, 2015 ) identified a mixture of an internal noise-reduction mechanism (to 46.89% ± 3.49% and 64.87% ± 4.37% of the pretraining levels in the high- and no-reward conditions, respectively, averaged across spatial frequencies; A a in Figure 2D ) and an external noise-exclusion mechanism (to 83.45% ± 4.78% and 83.35% ± 3.86% of the pretraining levels in the high- and no-reward conditions, respectively, averaged across spatial frequencies; A f in Figure 2D ; see PTM fitting in Supplementary Information for details). High reward enhanced internal noise reduction, t (9) = −3.253, p = 0.010, but the magnitudes of external-noise exclusion were comparable in the two reward groups, t (9) = 0.015, p = 0.988.…”

What is new in perceptual learning?

“…The good news continues in the contribution by Yan et al (2015). Myopic patients improved contrast sensitivity and visual acuity through perceptual learning, mainly due to a reduction of internal noise.…”