Monkeys Point to Objects They Don't 'See': How Similar is Human Sight

Humans are able to locate and even side-step objects in their peripheral vision, sometimes even before they perceive the object even being present. Now, it turns out that monkeys can do the same. Scientists have discovered that our relatives are able to locate where objects are without much more than a sideways glance.

In order to examine whether visually guided action and visual perception occurred independently in other primates, the researchers trained five adult rhesus monkeys. These monkeys performed a short-latency, highly stereotyped localization task. Using a touchscreen computer, the animals learned to press one of four locations where an object was briefly presented. They also learned to perform a detection task using identical stimuli, in which they had to report the presence or absence of an object by pressing two buttons.

"Knowing whether similar independent brain systems are present in humans and nonverbal animals is critical to our understanding of comparative psychology and the evolution of brains," said Lau Andersen, one of the researchers, in a news release.

So what did they find? It turns out that the monkeys were still able to locate targets that they could not detect. The animals performed the tasks very accurately when the stimuli were unmasked, and their performance dropped when visual masking was employed. However, the monkeys could still locate targets at masking levels for which they reported that no target had been presented.

The findings actually can't establish the existence of phenomenal vision in monkeys. However, it does reveal that they do have similar abilities to humans. Monkeys are apparently able to localize stimuli they do not perceive. These findings in particular are important for understanding the evolutionary relationships between humans and monkeys and also reveal a little bit more about human brain function.

The findings are published in the journal Animal Cognition.