Avi M. Aizenman¹ (), Zoe Goll², Karl R. Gegenfurtner³; ¹Giessen University

We adapted a paradigm from animal learning to investigate the stability of color category borders in humans using a VR videogame task. Observers held a colored saber in each hand and swiped approaching cubes which contained a colored stripe. Observers were instructed to use the saber whose color best matched the colored stripe. Saber colors were green and blue, or pink and purple, and the cube colors varied smoothly in fixed multiples of discrimination threshold. In a baseline block, observers were tested on a predetermined set of colors, where three of the in-between hues were ambiguous and close to the category border. We fit the saber choices with a psychometric function to determine the location and sharpness of the category border. Subsequent blocks shifted the tested color range toward one endpoint, and if observers’ color category borders were stable, there would be no difference between the baseline and shifted borders. Alternatively, observers could base their responses on the color difference between the cube and the saber only. In that case, the PSE would shift in the same direction as the shift in the colors tested. Our results show that observers exhibit a halfway shift of their category borders in the direction of the saber color shift. In follow-up studies, we found that this partial range effect persists even when equalizing the proportion of responses made with each saber color. We also found a comparable adaptation to the range when using green hues without a category border. This work suggests a very limited role of color categories for our task. We speculate that observers learn the task and quickly become adept at performing the match to sample task. This expertise may allow observers to respond automatically instead of focusing on the categorical distinction of the hues.

Acknowledgements: Alexander von Humboldt Fellowship to author AMA