Is there a cognitive bias against absolute synonymy? The current work explored this question via a miniature mini-artificial language experiment featuring iterated learning, which can amplify weak cognitive biases, as languages are sifted through multiple adult learners. Participants were taught two novel synonymous verbs in positive or negative sentences. Afterwards, they had to generalize the words to new positive or negative sentences. These sentences then served as the input sentences for the next participant in the diffusion chain and so on. Despite inconsistent input with regard to positive or negative meaning, participants differentiated the verbs. More than half of participants strongly differentiated them, specializing at least one term. However, transmission did not increase differentiation overall, suggesting that a bias against synonymy may encourage a minimally distinctive difference, not necessarily a systematic one, between synonyms.

Labels may play a role in the formation and acquisition of object categories. We investigated this using a free-categorization task, manipulating the presence or absence of labels and whether labels were random or reinforced one of two alternative categorization cues (taxonomic or thematic relationships). When labels were absent, participants used thematic and taxonomic cues equally to categorize stimuli. When present, labels were used as the primary cue for category formation, with random labels leading participants to attend less to taxonomic and thematic relations between stimuli. When labels redundantly reinforced either thematic or taxonomic cues, the use of the cue in question was boosted along with the use of labels as a cue for categorization. Most interestingly, in spite of previously observed associations between labels and taxonomic grouping, labels did not preferentially boost the use of either taxonomic or thematic cues in comparison with the other.