A research group from the University of Tübingen in Germany measured brain activity in crows performing a visual task to show the birds were capable of consciously perceiving sensory impressions.
The discovery is surprising because this had previously only been demonstrated in humans and other primates, which have completely different brain structures to birds.
“The results of our study open up a new perspective on the evolution of perceptual consciousness and its neurobiological boundary conditions,” Professor Andreas Nieder, an animal physiologist at the University of Tübingen, said.
The study, published in the journal Science, saw the research team train two crows to peck at a coloured light if they saw a visual stimulus appear on a screen.
Although the majority of these stimuli were clear, some were deliberately made so faint that the crows could not always detect them, producing different results from the birds.
The researchers recorded the activity of individual nerve cells in the brain as the crows performed the task and found they could predict what subjective experience the birds had with the stimulus based on the activity of the cells.
“Nerve cells that represent visual input without subjective components are expected to respond in the same way to a visual stimulus of constant intensity,” Professor Nieder said.
“Our results, however, conclusively show that nerve cells at higher processing levels of the crow's brain are influenced by subjective experience, or more precisely, produce subjective experiences.”
He added that this could mean the origins of consciousness were much older and more widespread in the animal kingdom than previously thought.
“The last common ancestors of humans and crows lived 320 million years ago,” he said.
“Perceptual awareness could possibly already have arisen then and have been inherited since then.”
Another possible explanation is that perceptual awareness in birds and primates could have developed independently of one another, according to the researcher.