23 — Crows Rival Monkeys in Cognitive Capacity

The pallium of the brain evolved in mammals to become cortex, the layered sheet of processor tissue that coats the mammalian brain. Birds, on the other hand, also inherited the pallium, but the modern bird-brain structure, considered “nuclear” (discrete brain areas have arisen that mostly keep to themselves) has been less studied.

This study compares the working memory and ‘bandwidth of cognition’ of crows with that of rhesus monkey. Two crows (Corvus corone) were given the same task as a prior study had given to rhesus monkey (Maccaca mulatta):

A group of colored squares are placed on a computer screen. The pattern then disappears, and is replaced a few seconds later by an identical copy but one of the squares has changed color.

Surprisingly — at least, surprising to me — the crows performed about as well on this task as the rhesus monkeys had.

The most interesting thing in this paper to me was the importance of contralateral versus ipsilateral confounding stimuli. The crows’ performance did not decline much when more squares were added to the contralateral visual field to the stimulus. That is, if the color-changing square was on the left, it didn’t matter how many squares were on the right side; the crow still picked the correct left-side square.

This, the researchers muse, might be due to the far more segmented nature of the avian brain: Unlike primate brains, where optic nerves decussate and split at the optic chiasm, crows’ optic nerve crossing is “complete.”

The authors also note that the crows slightly over-performed (compared to the monkeys) on small numbers of squares, and dramatically underperformed on large numbers of squares, suggesting technical differences in working-memory implementation across the species.