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G. Giraudet, L. Azavant; Tolerance and adaptation to blur during object localization in natural scene – Differences between emmetropic and myopic observers . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2776.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Previous works provide strong evidence that myopic observers do not respond to a blurred environment as emmetropic observers. However, most of these studies considered specific visual conditions: blur detection threshold or blurred letters recognition. Whatever the task, subjects were asked to perceive contrasted forms on a uniform background. These stimuli do not correspond to what usually feed our visual system. What will be the reaction of myopic and emmetropic subjects submitted to a transient blur constraint during an ecological visual situation? We hypothesized that myopes, being less sensitive to blur, will better preserve their performances faced to an increasing constraint than emmetropes. Furthermore, after a repeated exposure to filtered scenes, we assumed that myopes will adapt faster. The following experiment was carried out to test both hypotheses. Methods:Subject’s instructions were to localize targets in natural scenes. Six different targets were considered. Images were displayed for 100 ms with normal or low–pass filtered spatial frequency contents. Three levels of blur were investigated. Twenty subjects participated in the study. They were classified into two groups depending on their refractive error: emmetropes (plano, n = 10) and myopes (–0.75 to –3.00 D, n = 10). The ability to adapt to blur constraints was assessed repeating the experiment three times (3 series). Results:Proportion correct responses was analysed with a three way ANOVA including two within–subject (level of blur and series) and one between–subject factors (refractive error). Results showed that myopes performed better than emmetropes (p=0.002). Furthermore, myopes maintained their localization performances longer than emmetropes as the filtering level increased (p<0.001). Correct responses rates increased as the experiment was repeated (p<0.001). However, from the first to the second series, performances improvement of both groups was not different (p=0.769). Conclusions:The present experiment showed that myopes managed blur constraints more easily than emmetropes during target localization in natural scenes. These results confirmed our first hypothesis and previous findings on simple form perception: myopes are less sensitive to blur than emmetropes. The evolution of performances during repeated exposure did not confirm our second hypothesis. Myopes did not adapt faster to transient blur constraints than emmmetropes. Nonetheless, a perceptual adaptation could happen during the first series. Our method was not designed to assess such fast adaptation processes.
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