A new approach to the formation of equivalence classes in pigeons.

Jitsumori et al. (2002) worked with four pigeons in a lab. They used a simultaneous discrimination task with many reversals to build AB, CD, AC, and BD relations.

The birds saw colored shapes on a screen. Correct choices earned grain. The team flipped the correct choice several times to test if new untrained links would appear.

Only two of the four pigeons showed one new transitive relation after all the reversals. The other two birds never produced the emergent link.

The result shows limited equivalence class formation in pigeons. Success was possible but not reliable.

Ribeiro et al. (2017) also ran equivalence training, but with children with autism. Their kids learned symmetry yet never reached equivalence. Both studies share the same training label yet report weak or absent equivalence, highlighting that species and learner profile matter.

Marin et al. (2022) moved the work to adult humans and used real words and pictures. Their participants quickly formed large equivalence classes. The jump from pigeons to people, and from meaningless reversals to meaningful words, shows how language can unlock robust emergent relations.

Together the three papers trace a line: pigeons show fragile equivalence, kids with autism show partial success, and verbal adults show strong class expansion.

If you run equivalence checks with clients who have limited language, do not assume full classes will emerge. Start with simple symmetry probes and build up. When you add real words or personally relevant pictures, expect faster and larger class growth. Track each learner separately; the data say emergence can be hit-or-miss.