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Jyrki M. Rovamo, Dean R. Melmoth.; Scaling of both gratings size and contrast is necessary for equalising detection across eccentricities. Journal of Vision 2002;2(7):200. doi: https://doi.org/10.1167/2.7.200.
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© ARVO (1962-2015); The Authors (2016-present)
We have recently shown that contrast sensitivity for face (IOVS 41, 2000, 2811–19), letter (IOVS 41, 2000, S437) and word (IOVS 42, 2001, S160) recognition can be equalised across eccentricities by scaling face/letter size and contrast according to local spatial and contrast scales of the underlying visual mechanisms. However, sole spatial scaling has been reported to be sufficient to equalise simple grating detection across eccentricities (JOSA A 4, 1987, 1579–82 & 1583–93). Scrutiny of these detection results suggested that scaling of contrast might improve superposition of data curves from various eccentricities. To test this ‘double scaling’ hypothesis we measured contrast sensitivities in a 2AFC task corresponding to 84% correct correct grating detection as a function of grating size magnification (1.25–20.0 deg) at four eccentricities (0, 2.5, 5, and 10 deg). Extrafoveal detection performance was found to the same as that of the fovea when extrafoveal gratings were magnified and had higher contrast. Sensitivity curves had the same shape at all eccentricities but the curves were shifted along logarithmic size (magnification) and contrast axes, which allowed complete superposition by double scaling. Thus, even contrast sensitivity for simple grating detection can be properly equalised across eccentricities only by scaling both grating size and contrast according to local spatial and contrast scales of the underlying visual mechanisms.
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