The discrimination of discrete and continuous amounts in African grey parrots (Psittacus erithacus)
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A wealth of research in infants and animals demonstrates discrimination of quantities, in some cases nonverbal numerical perception, and even elementary calculation capacities. We investigated the ability of three African grey parrots (Psittacus erithacus) to select the largest amount of food between two sets, either discrete food items (experiment 1) or as volume of a food substance (experiment 2). The two amounts were presented simultaneously and were visible at the time of choice. Parrots were tested several times for all possible combinations between 1 and 5 seeds or 0.2 and 1 ml of food substance. In both conditions, subjects performed above chance for almost all combinations. Accuracy was negatively correlated with the ratio, that is performance improved with greater differences between amounts. Therefore, these results with both individual items and volume discrimination suggest that parrots use an analogue of magnitude, rather than object-file mechanisms to quantify items and substances.
KeywordsAfrican grey parrots (Psittacus erithacus) Analogue magnitude Substance Estimation of amounts
We wish to thank Marie Monbureau and Sara-Jane Vick for their suggestions on how to improve the manuscript and Aurore Chartier for her help in conducting the experiments. We also thank Mathieu Amy, Julie Chebaux, Colette Désaleux, Violaine Garcia-Fernandez, Philippe Groué, Valériane Jouffroy, Philippe Lenouvel, Alexandre Lerch, Magali Pasteau for taking care of the parrots. Funding for this research was provided by the 6th PCRD Nest Pathfinder “What it means to be human”. The experiments comply with the French laws concerning animal care.
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