A decades-old model of animal (and human) learning is under fire

The buzz of a notification or the ding of an email might inspire excitement—or dread. In a famous experiment, Ivan Pavlov (pictured) showed that dogs can be taught to salivate at the tick of a metronome or the sound of a harmonium. This connection of cause to effect—known as associative, or reinforcement learning—is central to how most animals deal with the world.