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Daphne Silvestre, Angelo Arleo, Remy Allard; Contrast sensitivity: Measuring late internal noise across spatial frequencies. Journal of Vision 2016;16(12):957. doi: 10.1167/16.12.957.
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© ARVO (1962-2015); The Authors (2016-present)
The dominant source of internal noise limiting contrast sensitivity depends on various parameters of the stimulus. For instance, early photon noise is the dominant source of internal noise at high spatial frequencies and low luminance intensities, whereas late cortical noise is the dominant source of internal noise at low spatial frequencies and high luminance intensities. This shift in the dominant source of internal noise is due to the fact that photon noise is inversely proportional to luminance intensity and independent of spatial frequency, whereas late cortical noise drops with spatial frequency and is independent of luminance intensity. Cortical noise has been measured only at low spatial frequencies and was found to drop linearly (Pelli, 1990). The purpose of our study was to measure the late internal noise (independent of luminance) over a wide range of spatial frequencies. Given that early noise decreases with luminance intensity, late noise is the limiting noise source at very high luminance intensities even for high spatial frequencies. The internal equivalent noise and the calculation efficiency were measured over a wide range of spatial frequencies (0.25 to 16 cpd) and luminance intensities (16 to 16261 Td). Calculation efficiency was found to be independent of spatial frequency and luminance intensity. At high luminance intensities, internal equivalent noise was independent of luminance intensity at all spatial frequencies tested, which implies that the internal noise limiting contrast sensitivity was not early photon noise but late noise. This late noise was found to drop non-linearly with spatial frequency. The drop was less steep at high spatial frequencies compared to the low spatial frequencies. Further studies are required to investigate the cause of this nonlinear relation between late noise and spatial frequency.
Meeting abstract presented at VSS 2016
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