Relative Contribution of Low and High Spatial Frequencies in Scene Perception: Differences Between Myopes and Emmetropes

Abstract

Abstract: : Purpose: Several studies showed that myopic observers better performed with blurred stimuli than emmetropes. This was true not only for text perception (Rosenfield, Abraham–Cohen, 1999, Opto. and Vis. Sc. 303–307; Thorn et al., 1996, Proceedings Vis. Sc. and its Appl. 135–138) but also in a more ecological frame of object localization in natural scenes (Giraudet, Azavant, 2004, suppl. IOVS E2776). Does it mean that myopic observers have a preference for low Spatial Frequencies (SF)? In practice, the relative contribution of low and high SF ranges has not been investigated. Indeed, previous studies only considered blurred visual environment that is removing the higher SF of the spectrum. The current work aimed to determine whether myopes would prefer low SF when they are displayed in competition with high SF. Methods: Subject’s instructions were to name verbally the category of the scene displayed. Four scene categories were considered: indoor, landscape, city and highway. Four types of test images were generated for each scene category: non–filtered, high–pass filtered (cut–off frequency: 6 cpd), low–pass filtered (cut–off frequency: 2 cpd) and hybrid images. Hybrid images were constituted by the low SF of one scene and the high SF of another scene (Schyns, Oliva, 1994, Psychol. Sc. 195–200). Images were displayed for 30 ms. Thirsty four young adults participated in the study. They were classified into two groups depending on their refractive error: emmetropes (plano, n = 15) and myopes (–0.50 to –7.00 D, n = 19). The 24 test images were displayed 6 times for each subject. Results: Proportions of correct responses of emmetropes were compared to those of myopes. Results showed that emmetropes and myopes performed at the same level for non–filtered, high–pass filtered and low–pass filtered images. However, when low and high SF were displayed simultaneously in hybrid images, myopes exhibited a strong bias in favour of the low SF whereas emmetropes did not show any preference. Conclusions: The current study showed that myopes had the same level of performance as emmetropes whatever the SF range when low and high SF were displayed separately. Myopes exhibited a significant preference for low SF only for hybrid images that is when they were in competition with high SF. Emmetropes allocated the same weight to low and high SF.

Keywords: myopia • scene perception • perception