Our Brains Can Quickly Spot Animals in a Scene
A new study may explain how humans can quickly determine if there is an animal present in a natural scene. This has been a bit of a mystery, because studies show that people can accurately determine whether a nature scene contains an animal in about a tenth of a second. This is too fast to allow for complex visual processing, however.
Our visual system has a hierarchical approach to visual processing. The primary visual cortex performs rapid basic image processing, like edge detection, movement, and three-dimensional relationships.
This information is then sent to the visual association cortex to do more complex processing such as recognizing a shape as a specific object. Still further processing adds more abstract information, such as categorization of the object and then finally assigning emotional and other context.
Recognizing that an animal is present in a scene seems to require categorization, which is a high level of visual processing, but people are able to do it in the time it takes for only primary visual processing, which is the mystery.
The new study, by Researchers at the University of Edinburgh and the Aix Marseille Université, analyzed hundreds of images and found that there are predictable differences between the relationships of edges in landscapes vs animals. Specifically, animals have more curved lines and short straight segments, while landscape have longer and more gently curved lines.
Characterizing the edges of an image requires only a low level of primary visual processing, therefore it is possible that humans can get a very quick impression of whether or not there is an animal in their visual field, and then more abstract processing can fill in the details.
The researchers showed that this explanation fits human performance. Further, when subjects have a false positive – when they react quickly as if there is an animal in the scene when there wasn’t, this is because the scene contains contours that mimic those of an animal.
The researchers also point to other research that shows that the necessary types of connections needed to do this type of image processing are present in the primary visual cortex of mammals.
This all makes evolutionary sense – mammal brains evolved to quickly determine if it is likely that an animal is present in their visual field, and then more detailed processing can tell them what type of animal and if it is a threat.
This might also explain the many false sightings of creatures like Bigfoot. A quick glance may only provide time for the person to see that there is a large animal in the woods, but not fill in the details. Their imagination then kicks in and fills in the details missed by the visual system.