Russian blues reveal the limits of language influencing colour discrimination.

Chromatic stimuli across a boundary of basic colour categories (BCCs; e.g. blue and green) are discriminated faster than colorimetrically equidistant colours within a given category. Russian has two BCCs for blue, sinij 'dark blue' and goluboj 'light blue'. These language-specific BCCs were reported to enable native Russian speakers to discriminate cross-boundary dark and light blues faster than English speakers (Winawer et al., 2007, PNAS, 4, 7780-7785). We re-evaluated this finding in two experiments that employed identical tasks as in the cited study. In Experiment 1, Russian and English speakers categorised colours as sinij/goluboj or dark blue/light blue respectively; this was followed by a colour discrimination task. In Experiment 2, Russian speakers initially performed the discrimination task on sinij/goluboj and goluboj/zelenyj 'green' sets. They then categorised these colours in three frequency contexts with each stimulus presented: (i) an equal number of times (unbiased); more frequent (ii) either sinij or goluboj; (iii) either goluboj or zelenyj. We observed a boundary response speed advantage for goluboj/zelenyj but not for sinij/goluboj. The frequency bias affected only the sinij/goluboj boundary such that in a lighter context, the boundary shifted towards lighter shades, and vice versa. Contrary to previous research, our results show that in Russian, stimulus discrimination at the lightness-defined blue BCC boundary is not reflected in processing speed. The sinij/goluboj boundary did have a sharper categorical transition than the dark blue/light blue boundary, but it was also affected by frequency and order biases, demonstrating that "Russian blues" are less well-structured than previously thought.