The role of similarity of stimuli and responses in learning by nectar-foraging bumble bees: a test of Osgood’s model

Abstract

Learning stimulus–response associations helps animals to adjust to changing environments. Sequentially learned associations may interact with each other, either reinforcing memory, a process referred to as ‘transfer’, or hindering memory, a process referred to as ‘interference’. According to Osgood’s (1949, Psychological Review, 56(3), 132–143) model, close similarity between new and previously learned stimuli can enhance the transfer of memory through a process of stimulus generalization. In contrast, the model proposes that if responses are different from those previously learned, generalizing stimuli may lead to confusion, resulting in the interference of memory. This model has primarily been applied in the context of human verbal learning. However, the interaction between stimulus similarity and response similarity is poorly documented in nonhuman animals, despite a growing body of literature suggesting that both vertebrate and invertebrate species share complex cognitive abilities similar to those found in humans. Here, we tested Osgood’s model using bumble bees (Bombus impatiens) foraging for sucrose on artificial flowers with varied colours (= stimuli) that required either legitimate visits or nectar robbing (= responses). Bees were first allowed to forage on one type of flower, then switched to another type of flower and finally returned to the initial flower type. We measured learning performance via flower-handling time and the number of failed visits. Consistent with Osgood’s model, bees made more failed visits when they switched between similarly coloured flowers requiring different foraging techniques but made fewer failed visits when switching between similarly coloured flowers with the same technique. Regardless of similarities in stimuli or responses, however, experienced bees were faster in handling flowers than were naïve bees. Results taken together thus provide mixed support for Osgood’s model. Possible explanations for the mixed results are discussed.