Data from: Superior discrimination for hue than for saturation; and an explanation in terms of correlated neural noise

The precision of human colour discrimination depends on the region of colour space in which measurements are made and on the direction in which the compared colours – the discriminanda – differ. Working in a MacLeod-Boynton chromaticity diagram scaled so that thresholds at the white point were equal for the two axes, we made measurements at reference points lying on lines that passed at 45° or -45° through the white point. At a given reference chromaticity, we measured thresholds either for saturation (i.e. for discriminanda lying radially along the line passing through the white point) or for hue (i.e. for discriminanda lying on a tangent of a circle passing through the reference point and centred on the white point). The discriminanda always straddled the reference point in chromaticity. The attraction of this arrangement is that the two thresholds can be expressed in common units: all that differs between saturation and hue measurements is the phase with which the short-wave signal is combined with the long-/middle-wave signal. Except for chromaticities very close to the white point, it appears to be a general law that saturation thresholds are higher than hue thresholds. We offer a possible explanation in terms of correlated neural noise.人类颜色辨别精度取决于测量所处的颜色空间区域，以及待比较颜色（判别色discriminanda）的差异方向。我们在经缩放的麦克劳德-博伊顿色度图（MacLeod-Boynton chromaticity diagram）中开展实验，该图表经缩放后使得白点处两个坐标轴的阈值相等。我们在穿过白点且呈45°或-45°的直线上的参考点处进行测量。在给定参考色度下，我们分别测量饱和度阈值（即待比较颜色沿穿过白点的径向分布时的阈值）与色调阈值（即待比较颜色位于以白点为圆心、过参考点的圆的切线上时的阈值）。所有判别色始终在色度上跨于参考点两侧。该实验设计的优势在于，两种阈值可采用统一单位表达：饱和度测量与色调测量的唯一区别，仅在于短波信号与长/中波信号结合时的相位差异。除了极接近白点的色度点外，饱和度阈值高于色调阈值似乎是一条普适规律。我们基于相关神经噪声（correlated neural noise）提出了一种可能的解释。