Carrion crows process visual motion signals at double the speed of monkeys

Carrion crows reach visual decisions in half the time required by monkeys, according to a new study published today. The findings challenge the long-held assumption that complex decision logic requires a specific type of brain tissue found only in mammals.

The research team from the University of Tübingen tested two hand-raised birds on the random-dot-motion task. This standard neuroscience experiment displays a cloud of flickering specks that drifts weakly in one direction. The subject must identify the direction of movement. In previous primate studies, this task revealed how neurons in the neocortex accumulate visual evidence over time until a firing threshold is reached, triggering a choice.

Birds do not possess a neocortex, leaving a gap in understanding how their brains handle similar cognitive processes. Andreas Nieder, a neurobiologist at the University of Tübingen, described this gap as the primary question of the study. He asked how a differently organized avian brain would encode decisions. His colleague Philipp Schmidbauer joined him in recording the brain activity of the two crows during the tests.

The setup mirrored the primate version exactly. The crows faced a touch-sensitive monitor displaying white dots on a black background. A subset of dots moved coherently to the left, right, up, or down. The birds reported their choice by pecking one of the targets flanking the display. A correct answer resulted in a mealworm reward. Nieder stated the team intentionally kept the task identical to the monkey version, noting the only difference was the method of response. Crows pecked to indicate their decision, whereas monkeys used eye movements.

The researchers varied the difficulty by altering the percentage of dots moving together. The easiest condition involved 81 percent of dots moving coherently. The hardest condition involved only 3 percent, a level barely distinguishable from random noise. The team also included a condition with 0 percent coherence, where no correct answer existed. The crows solved the task using the same mathematical logic as primates, despite their distinct brain organization.

The study indicates that a brain without a neocortex can arrive at decisions through a comparable process. The birds achieved these results twice as fast as the monkey benchmarks. The results were published in a study led by Nieder and Schmidbauer at the University of Tübingen.