Flexible Behavior or Flexible Methods? A Cross-Taxon Review of Experimental Designs in Reversal Learning
Nicolás Alessandroni, Rachael Miller, Drew M. Altschul, Lisa P. Barrett, Marina Bazhydai, Mahmoud M. Elsherif, Julia Espinosa, Biljana Gjoneska, Yseult Héjja-Brichard, Valeria Mazza, Annika Paukner, Ekaterina Pronizius, Michael J. Proulx, Muhammad A. J. Qadri, Olivia T. Reilly, Raoul Schwing, Carla Sebastián-Enesco, Vedrana Šlipogor, Alexandra A. de Sousa, Ingmar Visser, Justin Yeager, Martin Zettersten, Krista Byers-Heinlein, Josep Call, Lars Chittka, Ludwig Huber, Laurent PrétôtAbstract
Behavioral flexibility—the ability to adapt behavior in response to changing conditions—is commonly measured using reversal learning tasks, where individuals must inhibit a previously rewarded response and adopt a new one after contingencies change. Despite widespread use, task comparability across species remains unclear. We systematically reviewed 206 empirical studies (2014–2023) spanning eight taxa: invertebrates, fishes, amphibians and reptiles, birds, rodents, non-human primates, humans, and other mammals. We extracted species coverage, sampling, learning and reversal criteria, cue types, and outcome measures, and characterized cross-taxon variation using nonparametric tests, correlation analyses, linear discriminant analyses, and model-based robustness checks. We identify three methodological obstacles. First, research is highly imbalanced, concentrated on humans, birds, and rodents. Most animal diversity remains virtually untested, with under 1% of described species represented in five of the seven non-human taxa. Second, research is taxonomically fragmented: 99% of studies examine only one taxon, limiting direct comparisons. Third, methodological standards diverge dramatically across taxa. Humans consistently face the strictest learning criteria, while other taxa typically use lower thresholds. Mean reversal phases differ more than threefold across taxa: single-reversal designs predominate in amphibians and reptiles, fishes, and invertebrates, whereas multi-reversal protocols are relatively more frequent in humans and non-human primates. Sample sizes, evaluation window lengths, cue types, and outcome measures also show taxon-specific patterns. These systematic design differences complicate cross-taxon comparisons, blurring the line between true cognitive variation and methodological artifacts. Greater methodological coordination and broader taxonomic coverage are needed, and emerging large-scale collaborations offer a promising path forward.