Abstract
Background: Both long-term and short-term experience with object color affects color perception. Memory colors (typical colors of familiar objects such as fruit) draw perceived color towards them. Central-tendency bias (CTB) occurs when the perceived color of a stimulus held in memory shifts towards the average color of recent stimulus history. We studied how these biases develop: First, what is the time-course of CTB? Second, do memory colors start developing immediately upon exposure to shape-dependent hue distributions? Methods: Observers compared the hue of two stimuli in a 2IFC task. A 2-second delay separated the reference (first) and test (second) intervals. Two visually distinct 2D-shapes, "softy" and "spiky", were used. Both had five reference values ranging from blueish to greenish in CIELAB color space; softies were on average greener and spikies bluer but had one color in common. Reference and test were always the same shape except for the common reference color, for which reference and test were of different shape. On each trial, observers indicated whether the test appeared bluer or greener than the reference. A 1-1 staircase procedure controlled the test hue for each reference to track its perceived color. Results: In within-shape judgments, perceived color of the extreme references was biased towards the middle hues, consistent with CTB. This effect formed quickly: it appeared during the first 20 trials and was very prominent after 50-100 trials. Across-shape judgments showed, unexpectedly, a repulsive effect: The "softy" reference was matched by a bluer "spiky", and "spiky" reference by a greener "softy". Conclusion: Memory biases of perceived color develop rapidly and can be shape-dependent. The observed attractive and repulsive biases can be explained by shape-specific adaptation to color range, whereby hues are normalized with respect to the hue distribution separately for the two shapes, followed by a central-tendency bias.
Meeting abstract presented at VSS 2017