Prior associations affect bumblebees' generalization performance in a tool-selection task.

A small brain and short life allegedly limit cognitive abilities. Our view of invertebrate cognition may also be biased by the choice of experimental stimuli. Here, the stimuli (color) pairs used in the match-to-sample tasks affected the performance of buff-tailed bumblebees (). We trained the bees to roll a tool, a ball, to a goal that matched its color. Bees trained with a yellow-and-orange/red stimuli pair took more training bouts to reach our color-matching criterion than those trained with a blue-and-yellow stimuli pair. When assessing the bees' concept learning ability in a transfer test with a novel color, the bees trained with blue and yellow (novel color: orange/red) were highly successful, the bees trained with blue and orange/red (novel color: yellow) did not differ from random, and those trained with yellow and orange/red (novel color: blue) failed the test. These results highlight that stimulus salience can affect our conclusions on test subjects' cognitive ability. Therefore, we encourage paying attention to stimulus salience (among other factors) when assessing the cognition of invertebrates.