International Journal of Comparative Psychology

The purpose of this study was to examine the responses of a Steller sea lion to two consecutive commands. We conducted this study on one same subject, Hama, as a continuation of Sasaki et al. (2022), which examined whether the Steller sea lion can discriminate human vocal commands. In Sasaki et al. (2022), commands were presented individually to examine the accuracy rate for each command. In the present study, we observed how Hama responded to the rapid presentation of two consecutive commands. The commands were presented in 20 different orders and combinations as 20 command combination patterns using five different commands. The results showed that Hama responded to 12 command combination patterns by performing behaviors corresponding to two consecutive commands. Hama performed the two behaviors in sequence in 8 of the 12 command combination patterns. The responses to the other four command combination patterns were combined single behaviors that combined the behaviors indicated by the two consecutive commands and that were already connected to different single commands. Although the combined single behaviors were not simple combinations of behaviors induced by the two consecutive commands, the combined single behaviors included the common body parts (e.g., fore flippers) or common action types (e.g., rotation) of behaviors induced by each command in the two consecutive commands. These results not only indicate that Hama could understand multiple linguistic information, but also suggest the possibility that Hama spontaneously formed categories based on the learned commands.