Auditory‐visual equivalence learning by marine mammals.

Forty years ago Sam Ridgway began pioneering research on the brain and sensory systems of marine mammals. Our paper honoring Sam reviews studies on the abilities of dolphins and California sea lions to integrate and classify information coming from different sensory channels in cross‐modal matching‐to‐sample tasks. Following echoic recognition of an object, a dolphin that is permitted to investigate objects visually but not echoically can readily learn and remember that earlier reflected sound cues are related to the currently reflected light cues. A California sea lion has shown that it can also integrate auditory‐visual information into something resembling equivalence classes. In these studies the sea lion was taught to relate an array of individual auditory signals (e.g., “ringing bell” and “wailing siren”) to several individual members of two previously established visual equivalence classes (“numbers” and “letters”). Following the training phase it was later determined that the sea lion had knowledg...