Tübingen Study Reveals Crows Process Visual Ambiguity in Half the Time of Monkeys

Carrion crows resolve ambiguous visual information using the same mathematical logic as primates but do so in half the time, according to a study published by researchers at the University of Tübingen.

The experiment utilized the random-dot-motion task, a standard procedure in cognitive science where subjects observe a cloud of flickering dots that drifts weakly in one direction. The subject must determine the direction of movement. In primates, neurons in the neocortex accumulate visual evidence over time. Their firing rates rise until they cross a specific threshold, prompting the animal to commit to a choice. Birds lack this neocortical structure, leaving the mechanism for their similar decision-making processes unclear.

Andreas Nieder, a neurobiologist at the University of Tübingen, and colleague Philipp Schmidbauer tested two hand-raised carrion crows to address this gap. The birds faced a touch-sensitive monitor displaying white dots on a black background. A portion of the dots moved coherently left, right, up, or down. The crows indicated their chosen direction by pecking targets flanking the display, receiving a mealworm for correct answers.

The researchers maintained the experimental setup identical to previous monkey trials to ensure comparability. Nieder noted the only difference was the method of response. "We intentionally wanted to have exactly the same random-dot motion task," he 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 team varied task difficulty by adjusting the percentage of dots moving coherently. The easiest condition involved 81 percent of dots moving together, while the hardest involved only 3 percent, a signal barely distinguishable from noise. A condition with zero coherent movement served as a control with no correct answer.

The results showed that the crows used the same evidence-accumulation logic observed in primates. Despite the structural differences in their brains, the birds reached their decisions twice as fast as the monkeys did in comparable tasks.

Nieder described the finding as a resolution to a long-standing question about avian cognition. "This was the big question," he said. "How [would] a differently organized avian brain encode decisions?" The data confirms that a brain without a neocortex can process visual ambiguity through a comparable, albeit faster, computational process.