Monkeys Locate Objects They Do Not Report Seeing

Monkeys are able to detect objects they do not report seeing, according to a study published in the journal Animal Cognition.

Humans are able to identify and even avoid objects in their peripheral vision even before fully perceiving the object. Led by Lau Andersen of the Aarhus University in Denmark, researchers ventured to discover whether primates are also capable of visually guided action and visual perception.

They trained five adult male rhesus monkeys to touch one of four locations on a touchscreen computer whenever an object briefly appeared there. They were also trained to perform a detection task using identical stimuli. In this task they were taught to report the presence or absence of an object by pressing one of two buttons.

The tasks are easily comparable to human abilities and cognition because both techniques are used to test people, according to the study.

The researchers then used a method known as "visual masking" in order to gradually and systematically reduce how easily a target was processed.

The results showed that the monkeys were able to locate targets they could not detect, performing well when the stimuli were unmasked and struggling when visual masking was used. However, the monkeys were able to locate targets at masking levels at which they had reported no target having been presented.

This discrepancy, according to the researchers, directly parallels to dissociation of conscious and unconscious vision in humans.

"Knowing whether similar independent brain systems are present in humans and nonverbal species is critical to our understanding of comparative psychology and the evolution of brains," Andersen said.

The study was conducted at the Yerkes National Primate Research Center of Emory University.