Our eyes view the world from two different vantage points. That means we see the world in three dimensions partially because our brain compares the differences between these two images, and uses this information to compute depth and distance. This process is called stereopsis.

To learn what might happen in the human brain during stereopsis, researchers study the brains of monkeys. They put electrodes in the monkey's brain to record the electrical activity of single visual brain cells. 

They found that some of these cells are tuned to detect differences between the two eyes' images that indicate depth and distance. 

There are some animals, however, that are very different from humans. For example, neuroscientists know that some insects, such as the praying mantis, have a form of stereopsis. Although their brains are much smaller and organized differently than ours.

In 2019 a team of European neuroscientists reported they had used an electrode to record electrical activity in single visual brain cells involved in stereopsis in a mantis.

The scientists put tiny glasses on the mantis, like the ones humans use to watch a 3-D movie. Then they showed the mantis a 3-D movie involving simple moving bars and disks. 

They found that some visual cells in the mantis' brain were tuned to detect differences between the images of the two eyes that indicate distance. 

They were surprised by how similar the stereopsis cells in the mantis were to those in the monkeys. Their findings might imply there are general brain principles for stereopsis in all animals. 

Sources and Further Readings

• Rosner, R., et al. (2019). A neuronal correlate of insect stereopsis. Nature Communications. 10 (2845).