Artificial language comprehension and size transposition by a California sea lion (Zalophus californianus)

A variation of the conditional discrimination procedure defines relations between stimuli (for example, gestural signs and their referents), and it has been used to study language comprehension in California sea lions. The animals followed instructions given by a trainer's gestures designating properties of size, brightness, and location (adjectives), types of objects (nouns), and actions (verbs). The signs can be combined and recombined according to a conditional sequence or syntax. In this study, we sought to determine whether adjectives for size had an absolute meaning, that is, small and large, as well as a comparative meaning, that is, smaller and larger. A sea lion, Rocky, was given experience with signs designating standard small and large spheres in commands like LARGE BALL MOUTH. On transposition tests, the small ball was removed and the previously designated large ball was paired with an even larger one. The results showed that the adjectives had both an absolute and a relative meaning. Object choices and searching behavior revealed that the sea lion processed information about the relation of size as well as about the specific characteristics of the sizes of spheres that instantiated the relations.