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Antoine Barbot, John Pirog, Cherlyn Ng, Geunyoung Yoon; Neural adaptation to optical aberrations through phase compensation. Journal of Vision 2020;20(11):1130. doi: https://doi.org/10.1167/jov.20.11.1130.
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© ARVO (1962-2015); The Authors (2016-present)
Background–Human vision is intrinsically limited by optical blur, which degrades retinal image quality by reducing contrast and disrupting the phase of transmitted spatial frequency (SF) information. Many studies have shown that the visual system can compensate for blur-induced reductions in contrast and visual acuity via gain control mechanisms. However, perceptually relevant information about the structure of an image is almost exclusively contained within the phase spectrum, rather than the amplitude spectrum. Yet, it is unclear whether the brain can compensate for phase scrambling effects of optical blur. Here, we introduce a novel approach combining visual psychophysics and adaptive optics (AO) techniques to assess whether neural adaptation to blur compensates for disrupted phase congruency induced by optical aberrations, following both short-term and long-term exposure to degraded retinal images.
Method and Results–Participants judged the appearance of suprathreshold compound grating stimuli consisting of two sinusoids (frequencies f and 2f) varying in relative phase. AO was used to fully correct or induce optical aberrations while measuring perceived phase congruency. Human participants were sensitive to both physical phase shifts and blur-induced alterations of phase congruency. Under AO-induced optical aberrations, the magnitude and direction of perceived phase shifts matched predictions from optical theory. Moreover, during short-term adaptation (~1h) to AO-induced blur, we found that the magnitude of the perceived phase shift decreased with time and was followed by an after-effect in the opposite direction, consistent with neural compensation to phase spectra. A control condition ruled out changes in response bias or fatigue as possible explanations. Finally, patients with keratoconus–a corneal disease resulting in long-term adaptation (up to 10-20 years) to severe optical aberrations–exhibited altered phase congruency when tested under aberration-free AO condition.
Conclusion–Our findings reveal the existence of neural compensation mechanisms to phase spectra that attenuate the impact of blur on phase congruency over time.
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