Adaptation to astigmatic blur

Abstract

Adapting to blurred or sharpened images alters the perceived focus of subsequently viewed images. We examined whether these adaptation effects could arise from actual sphero-cylindrical refractive errors, by testing aftereffects in images simulating second-order astigmatism. Image blur was varied from negative (vertical) through isotropic to positive (horizontal) astigmatism while maintaining constant blur strength. A 2AFC staircase was used to estimate the stimulus that appeared isotropically blurred before or after adapting to images with astigmatism. Adaptation to horizontal blur caused isotropically blurred images to appear vertically biased and vice versa, shifting the perceived isotropic point toward the adapting level. Aftereffects were similar for different types of images and showed partial selectivity so that strongest effects generally occurred when testing and adapting images were the same. Further experiments explored whether the adaptation depended more strongly on the blurring or “fuzziness” in the images vs. the apparent “figural” changes introduced by the blur, by comparing how the aftereffects transfer across changes in size or orientation. Our results suggest that strong selective adaptation can occur for different lower order aberrations of the eye and that these may be at least partly driven by the apparent figural changes that blurring introduces into the retinal image.

Blur Adaptation with Source and Observer Methods

“…The applications of psychophysical procedures have been seen in the studies on blur adaptation to astigmatism (Sawides et al 2010) and higher order aberrations (Sawides et al 2011a) in the literature.…”

“…There are two important outcomes reported in the literatureperceived isotropic point (Sawides et al 2010) and subjective best focus point (Sawides et al 2011a). …”

“…Adaptations to astigmatism blur and higher order aberrations (HOAs) blur have been studied only using source methods (de Gracia et al 2010, Sawides et al 2010, de Gracia et al 2011, Sawides et al 2011a, Sawides et al 2011b, Sawides et al 2012, Vinas, Sawides, De Gracia and Marcos 2012, Sawides et al 2013). These studies were performed using an AO system and adaptive psychophysical procedures were used to quantify the blur adaptation.…”

“…The 2 AFC staircase procedure has been used for determining the adaptation to astigmatism blur (Sawides et al 2010). Lower order aberrations and HOAs were corrected with an adaptive optics system, followed by presentation of astigmatic blur stimuli.…”

“…This perceived isotropic point was measured as the average value of last 12 reversals. Sawides et al (2010) performed five different experiments for astigmatism blur adaptation. In the first experiment, to check the selectivity towards the axis of astigmatism subjects adapted to a single image of a human face blurred with ±0.3 µm horizontal and/or vertical astigmatism.…”