Crows make visual calls in 0.5 seconds
Researchers at the University of Tübingen found that carrion crows process visual motion data at twice the speed of primates.
By Carmen Wojcik ·
0.5 seconds. That is how long it takes a carrion crow to reach a decision about moving visual data. The time is half as fast as the speed at which monkeys process the same information.
The speed difference comes from a study by neurobiologist Andreas Nieder and colleague Philipp Schmidbauer at the University of Tübingen. They tested two hand-raised carrion crows on a task typically used for primates. The results show that birds without a neocortex can process visual evidence using the same mathematical logic as primates.
The test is called the random-dot-motion task. A cloud of flickering specks drifts weakly in one direction. The subject must determine if there is motion and identify the direction. In primates, neurons in the neocortex collect this visual evidence over time. Their firing rates climb until they cross a threshold. At that point, the animal commits to a choice.
Birds do not have a neocortex. This structural difference left a gap in scientific understanding. "This was the big question," Nieder said. "How [would] a differently organized avian brain encode decisions?"
Nieder and Schmidbauer set up an identical environment for the crows. The birds sat in front of a touch-sensitive monitor displaying white dots on a black background. Some fraction of the dots drifted together to the left, right, up, or down. The crows reported the direction by pecking one of the targets flanking the display. A correct answer earned a mealworm.
The researchers varied the difficulty by changing how many dots moved together. At the easy end, 81 percent of the dots moved coherently. At the hardest end, 3 percent did, barely distinguishable from noise. The team included a zero percent condition with no correct answer.
"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."
The crows solved the task using the same mathematical logic as primates. Their brain activity followed the same accumulation pattern. The speed at which they reached a decision was double that of the monkeys. The finding indicates that a brain without a neocortex can arrive at decisions through a comparable process.
