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Angela M. Brown, Delwin T. Lindsey, Kevin M. Guckes; The Measurement of Infant Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5723. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a way to measure infant contrast sensitivity using a single stimulus. Others have measured the multiple parameters of the full contrast sensitivity function (CSF) using sine-wave gratings at multiple spatial frequencies (Adams et al, Optom Vis Sci, 1992), a lengthy and inconvenient method. Instead, we propose using a single, very low-spatial-frequency square-wave grating to measure the maximum of the CSF, without knowing at what spatial frequency it occurs. The key insight is that the amplitude of the harmonics in a square wave varies inversely with spatial frequency, whereas their packing density varies directly with spatial frequency. Thus, the spatial frequency channels all receive approximately equal stimulation: the low frequency channels detect fewer, higher-amplitude harmonics, whereas the high frequency channels detect more, lower-amplitude harmonics. Therefore the contrast sensitivity for a low-spatial-frequency square-wave will be constant and either equal to the maximum of the sine-wave CSF (channels from Wilson & Gelb, Vis Res, 1984), or 0.13-0.33 log units below the maximum (channels from Majoj et al, Vis Res, 2002). Classic adult data (Nachmias, JOSA, 1967; Campbell & Robson, J Physiol, 1968) are consistent with this prediction. Here, we report the contrast sensitivity of normal infants, measured using a conventional CSF and a low-frequency square-wave stimulus.
We tested 93 normal 4-month-olds, using horizontal 24° x 24° gratings and forced-choice preferential looking: we measured the sine-wave CSF (12-16 infants at each of 5 spatial frequencies) and we measured contrast sensitivity using a 0.125 cy/deg square-wave grating (13 infants).
The square-wave contrast sensitivity was 0.16 (SE=0.07) log units below the maximum sensitivity of the CSF, which was 20% and occurred at 1 cy/deg.
The precision of the measurement does not allow us to decide between the two channels models, but it does suggest that measurement using a low-spatial-frequency square wave can approximate the maximum of the sine-wave CSF. A clinical test based on a low spatial frequency square wave will allow the clinician to estimate the maximum of the contrast sensitivity function in a single measurement, without knowing the spatial frequency at which it occurs. A test of the maximum of the CSF will provide a measure of the overall visual performance of infant, toddler, and handicapped patients who cannot read an eye chart.
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