In animals and humans, a looming threat triggers the same kind of behavior - freezing followed by flight.

The uniform nature of this response suggests that the perception and processing of approaching motion is clearly defined and embedded in the brain.

Nerve cells for detection of approaching objects

As the researchers report in the latest issue of Nature Neuroscience, various types of retinal cells are involved in this perceptual process. An important role is played by the bipolar cells which lie just below the photoreceptors. Two types of bipolar cells are distinguished: those that become active in brighter light (known as ON cells) and those that respond to dimmer light (OFF cells).

For the eye, the image of an approaching object consists of a constantly expanding area of darkness. Therefore, as an object approaches, increasing numbers of OFF bipolar cells respond to this stimulus and transmit this signal to the next layer of retinal cells - the ganglion cells. These integrate the signal and transmit it to the brain.

The same system is shut of when faced with laterally moving objects: here the lateral motion activates amacrine cells, another cell type in the retina, which shut down the information flow.

Rapid processing of this information is often a matter of life or death - especially in the natural world, when an animal is suddenly confronted with a predator.

"Mouse retina with labeled ganglion cells. (Credit: Image courtesy of Friedrich Miescher Institute for Biomedical Research)"

Source: Friedrich Miescher Institute for Biomedical Research