Crows Crack Visual Tests in Half the Time Monkeys Need

Two carrion crows ran the same visual motion test routinely given to monkeys and reached their answers in about 0.5 seconds, roughly half the time primates take, while following the same decision-making rules. The work, led by University of Tübingen neurobiologist Andreas Nieder and colleague Philipp Schmidbauer, addresses a long-standing question: how do birds make such calls without a neocortex, the brain layer where primate decisions are thought to form? "This was the big question," Nieder said. "How [would] a differently organized avian brain encode decisions?"

The random-dot-motion task has been a standard tool in primate research. A cloud of flickering specks drifts slightly in one direction, and the subject judges whether motion exists and where it points. In primates, neurons in the neocortex gather evidence over time until their firing rate crosses a threshold, and the animal then commits to a choice.

The Tübingen team handed the identical setup to two hand-raised carrion crows. The birds sat before a touch-sensitive monitor showing white dots on black, with some share of dots drifting left, right, up or down. The crows pecked a target beside the display to answer, earning a mealworm for a correct call. "We intentionally wanted to have exactly the same random-dot motion task," Nieder said. "The only difference was that the crows had to peck to indicate their decision, whereas monkeys were indicating by making an eye movement."

To vary difficulty, the researchers set how many dots moved together. At the easy end, 81 percent of dots drifted coherently; at the hardest, 3 percent did, barely above noise. A zero percent condition was also included, in which no correct answer existed.

The crows solved the task through the same mathematical logic primates use, arriving at their answers in about half the time monkeys need. The result shows a brain without a neocortex can reach a decision by a comparable process.