Nonhumans have not yet shown stimulus equivalence

Area of Science:

• Behavioral Psychology
• Animal Cognition
• Learning Theory

Background:

• Recent studies have claimed the discovery of stimulus equivalence in nonhuman subjects.
• These claims are based on experimental procedures that require careful scrutiny regarding their methodology and interpretation.

Purpose of the Study:

• To critically evaluate recent claims of stimulus equivalence in nonhuman animals.
• To assess whether the experimental designs and data presented in these studies meet the established criteria for stimulus equivalence.

Main Methods:

• Analysis of two recent publications reporting stimulus equivalence in nonhumans.
• Examination of the experimental procedures, including training components and derived relations.
• Evaluation of the definitions of stimulus equivalence used in the studies.

Main Results:

• The first study trained all components but failed to demonstrate derived stimulus relations, a key characteristic of equivalence.
• The second study proposed a definition of stimulus equivalence that conflates it with functional stimulus classes, rendering the data irrelevant to the established concept.
• Neither study successfully demonstrated stimulus equivalence in nonhumans according to established scientific definitions.

Conclusions:

• Stimulus equivalence has not yet been conclusively demonstrated in nonhuman animals.
• Methodological and definitional issues in recent studies prevent the acceptance of their findings.
• Further research with rigorous designs is needed to explore the potential for stimulus equivalence in nonhumans.