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Ichiro Kuriki; Chromatic contrast sensitivity during slow temporal modulation in surrounding area. Journal of Vision 2004;4(8):320. doi: 10.1167/4.8.320.
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[Purpose] Dynamic changes in chromatic contrast-sensitivity induced by changes in contrast at surrounding area have been studied at relatively faster temporal frequencies (>1.0 Hz). This study investigates changes in sensitivity to chromatic contrast- during slow temporal modulation at the surround area. [Method] Stimulus was a mosaic pattern of regularly aligned squares (0.25 deg × 0.25 deg). Colors of mosaic elements distributed around equal-energy white along one of the DKL axes within a certain range. The elements in the center of the screen formed a probe area (2deg × 2deg), which was separated from the surround with a thin dark gap. Colors in the probe were determined independent of the surround. The probe was presented with a temporal envelope of 0.4 Hz raised-cosine waveform. Temporal modulations in the surrounding area consisted of four phases: gray, increasing chromatic contrast, hold at the maximum and decreasing contrast. The probe was presented every 5s. The observer's task was to discriminate color of the probe; whether the probe was modulated in L−M direction or other (S or luminance direction). Contrast-modulation thresholds were estimated by fitting psychometric functions to the data. [Results] Changes were observed in both thresholds and slopes of psychometric functions. The threshold elevations were observed in the phases except the gray phase. The change in the slope (which stands for standard deviation for the fitted cumulative Gaussian) was lager in the dynamic (increasing and decreasing) phases. [Discussions] The changes in the slope of psychometric function mean the changes in uncertainty of the colorfulness perception. It may probably mean that temporal modulations in the surrounding area induced noise at the probe region to make the signal for the probe less convincing. This suggests the possibility that the sensitivity to the colorfulness is dynamically adjusted to maintain the level of signal-to-noise ratio.
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