A plethora of studies demonstrate animal numerical competence, but their understanding of a numerical middle is unknown.
Monkeys played a video game and learnt to select the middle item in a three items series. At test, they transferred the learnt rule to longer series composed of 5,7 or 9 items. The monkey could have used a spatial or numerical strategy. To dissociate between these, we used asymmetric sequences where the spatial middle and numerical middle were different items. Monkeys selected only the numerical middle. Middle identification is part of the suite of abilities supported by the animal number sense.
Rugani R, Platt ML, Chen Z, EM Brannon . 2022 Relative numerical middle in rhesus monkeys. Biol. Lett. 20210426. https://doi.org/10.1098/rsbl.2021.0426
Funding. European’s Union Horizon 2020 Research and Innovation program under the Marie Sklodowska-Curie Grant/Award Number: 795242 and NIH/NIMH grants (grant nos. R37MH109728 and R01MH108627)