Carrion Crows Solve Visual Tasks at Twice the Speed of Monkeys
Neurobiologists found that birds reach decisions using the same mathematical logic as primates, but they do so in half the time.
By Leila Reynolds ·
Researchers at the University of Tübingen determined that carrion crows reach visual decisions at double the speed of primates. The team demonstrated that these birds utilize the same mathematical logic for decision-making as monkeys, despite possessing a brain structure that lacks the neocortex found in mammals.
The study addresses a long-standing question in neuroscience regarding how differently organized avian brains encode decisions. Andreas Nieder, a neurobiologist at the University of Tübingen, noted that the absence of a neocortex in birds left the mechanism for complex choices unclear. He described this as the central question driving the research.
To test this, Nieder and colleague Philipp Schmidbauer administered the random-dot-motion task to two hand-raised carrion crows. This specific experiment has previously established that primate neurons in the neocortex collect visual evidence over time. In primates, neural firing rates increase until they cross a threshold, triggering a committed choice.
The experimental setup mirrored the standard monkey protocol exactly. The crows sat before a touch-sensitive monitor displaying white dots on a black background. A portion of the dots drifted in a specific direction, while the rest moved randomly. The birds indicated their perception of direction by pecking targets flanking the screen, with a correct answer rewarding them with a mealworm.
Nieder emphasized that the team intended to replicate the monkey task precisely. The only procedural difference involved the method of response; while monkeys used eye movements to signal a decision, the crows used pecks. The researchers adjusted difficulty by varying the percentage of dots moving coherently. This ranged from 81 percent, which is easily discernible, down to 3 percent, which is nearly indistinguishable from noise. A condition with zero coherent movement was also included to represent tasks with no correct answer.
The data showed that the crows solved the task using the same cumulative evidence process observed in primates. However, the birds completed the decisions twice as quickly as the monkey subjects. This outcome suggests that a brain without a neocortex can execute comparable decision processes.
The findings indicate that the specific architecture of the neocortex is not strictly required for this type of rapid visual processing. The study provides evidence that different neural systems can converge on similar computational solutions for handling ambiguous sensory information.
