Louis M. Herman, whose seminal research demonstrated that dolphins could understand and respond to language transmitted by sound and visual signals, and whose research survived the criminal release of two trained dolphins by disgruntled former employees, died on Aug. 3 in Honolulu. He was 86.

The cause was bile duct cancer, his daughter, Elia Yvette Kamalei Herman, said.

Early in his career, Dr. Herman, a New York City native, made the shift from a behavioral psychologist studying decision-making to an expert in animal language and oceanography.

More than two decades of experiments at his Kewalo Basin Marine Mammal Laboratory in Honolulu proved that dolphins were the cognitive cousins of chimpanzees. By one measure, arguably, the dolphins were more advanced.

“In contrast to the learning process that seems required for chimpanzees, the dolphins at our laboratory proved capable of understanding gestural language instructions given through television images of people the very first time they were exposed to television,’’ according to the Dolphin Institute, which Dr. Herman co-founded in Honolulu with Adam Pack in 1993 to support research and conservation.