Sharpness overconstancy: the roles of visibility and current context

Galvin, Susan J.; O’Shea, Robert P; Squire, Abigail M.; Hailstone, Diane S.

doi:10.1016/s0042-6989(98)00306-x

Cited by 20 publications

(19 citation statements)

References 17 publications

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“…In normal viewing conditions, objects in the peripheral visual space are not perceived to be very blurry though we constantly experience poor image quality in the periphery due to the existing peripheral optical errors. In fact, previous studies have shown that blurred edges are perceived to be sharper in peripheral vision (Galvin, O'Shea, Squire, & Govan, 1997;Galvin, O'Shea, Squire, & Hailstone, 1999). In this context, it should be noted that the +2.00 D in the present study was introduced over the existing peripheral refractive errors and, as the spherical equivalent in 20°eccentricity was myopic in all four subjects, gave a further increase in peripheral refraction.…”

Section: Large Field Blur Stimulus Gave No Improvement After Adaptationsupporting

confidence: 40%

Blur adaptation: Contrast sensitivity changes and stimulus extent

et al. 2015

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A prolonged exposure to foveal defocus is well known to affect the visual functions in the fovea. However, the effects of peripheral blur adaptation on foveal vision, or vice versa, are still unclear. In this study, we therefore examined the changes in contrast sensitivity function from baseline, following blur adaptation to small as well as laterally extended stimuli in four subjects. The small field stimulus (7.5° visual field) was a 30min video of forest scenery projected on a screen and the large field stimulus consisted of 7-tiles of the 7.5° stimulus stacked horizontally. Both stimuli were used for adaptation with optical blur (+2.00D trial lens) as well as for clear control conditions. After small field blur adaptation foveal contrast sensitivity improved in the mid spatial frequency region. However, these changes neither spread to the periphery nor occurred for the large field blur adaptation. To conclude, visual performance after adaptation is dependent on the lateral extent of the adaptation stimulus.

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Section: Large Field Blur Stimulus Gave No Improvement After Adaptationsupporting

confidence: 40%

Blur adaptation: Contrast sensitivity changes and stimulus extent

et al. 2015

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“…Overall, the perception of blur is a complex process that depends on the eye's optical quality (i.e., aberrations) as well as both retinal and higher level neurophysiology (Ciuffreda et al, 2007; Mather & Smith, 2002; Wang & Ciuffreda, 2004, 2005a, 2005b). Motion, visual attention, sharpness overconstancy, and target attributes such as luminance, contrast, texture, and size also contribute to the perception of image blur (Christman, 1990; Galvin, O'Shea, Squire, & Hailstone, 1999; Pääkkönen & Morgan, 1994; Wang & Ciuffreda, 2004, 2005b). …”

Section: Introductionmentioning

confidence: 99%

Blur perception throughout the visual field in myopia and emmetropia

et al. 2017

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We evaluated the ability of emmetropic and myopic observers to detect and discriminate blur across the retina under monocular or binocular viewing conditions. We recruited 39 young (23–30 years) healthy adults (n = 19 myopes) with best-corrected visual acuity 0.0 LogMAR (20/20) or better in each eye and no binocular or accommodative dysfunction. Monocular and binocular blur discrimination thresholds were measured as a function of pedestal blur using naturalistic stimuli with an adaptive 4AFC procedure. Stimuli were presented in a 46° diameter window at 40 cm. Gaussian blur pedestals were confined to an annulus at either 0°, 4°, 8°, or 12° eccentricity, with a blur increment applied to only one quadrant of the image. The adaptive procedure efficiently estimated a dipper shaped blur discrimination threshold function with two parameters: intrinsic blur and blur sensitivity. The amount of intrinsic blur increased for retinal eccentricities beyond 4° (p < 0.001) and was lower in binocular than monocular conditions (p < 0.001), but was similar across refractive groups (p = 0.47). Blur sensitivity decreased with retinal eccentricity (p < 0.001) and was highest for binocular viewing, but only for central vision (p < 0.05). Myopes showed worse blur sensitivity than emmetropes monocularly (p < 0.05) but not binocularly (p = 0.66). As expected, blur perception worsens in the visual periphery and binocular summation is most evident in central vision. Furthermore, myopes exhibit a monocular impairment in blur sensitivity that improves under binocular conditions. Implications for the development of myopia are discussed.

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“…Visual spatial attention is mostly focused on the fovea, so much so that eye movements are called overt attention, and we seem to confuse the phenomenal characteristics of foveal visual perception with visual perception in general. As another example, contours in peripheral vision appear sharp (3) (cf Galvin, O'Shea, Squire, & Govan, 1997;Galvin, O'Shea, Squire, & Hailstone, 1999), even though acuity, which would be thought to be at the basis of perceived sharpness, is drastically reduced there.…”

Section: Introductionmentioning

confidence: 99%

Dancing Letters and Ticks That Buzz around Aimlessly: On the Origin of Crowding

Strasburger

2014

Perception

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Abstract. When we see an object, we know where it is. Or do we? Perhaps not in indirect vision, as was observed by the gestalt psychologist Korte in 1923. Objects and object parts appear to 'dance around', and these phenomena may underlie a part of what is called the crowding effect today. From Korte's account of pattern recognition in indirect vision, I select two phenomena: a loss of the positional code for letter parts and a loss of the same for whole letters. Using these examples, I present a novel, speculative explanation for a contradiction in the literature: patterns located more peripherally than a target show more interference than do more centrally located patterns, yet for whole-letter confusions the asymmetry is the other way round. The inward, not the outward, flanker is increasingly confused with a target at increasing target eccentricities. I propose that feature-binding decreases with eccentricity such that free-floating letter parts more often intrude from the periphery and whole letters from the centre. I conclude with a few remarks on computational modelling as, hopefully, a challenge to neural computationalists.

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Sharpness overconstancy: the roles of visibility and current context

Cited by 20 publications

References 17 publications

Blur adaptation: Contrast sensitivity changes and stimulus extent

Blur adaptation: Contrast sensitivity changes and stimulus extent

Blur perception throughout the visual field in myopia and emmetropia

Dancing Letters and Ticks That Buzz around Aimlessly: On the Origin of Crowding

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