It happens automatically and so quickly that most people probably never question the process of vision. Although it starts with the eyes, the majority of the work is performed in stages by cooperating layers of neural regions in the brain. As such, the underlying mechanism behind seeing and recognizing objects has long been of interest to neuroscientists. A team of researchers from The Johns Hopkins University’s Zanvyl Krieger Mind/Brain Institute have published a report in a recent issue of the journal Neuron describing the advances they have made towards understanding the process.
Object recognition may seem like an instantaneous process, but behind the scenes the neural structures of the brain are actually very quickly reconstructing the object from its constituent parts. When you see a letter or a number, the visual input arrives in pieces at multiple regions in the first neural stage. One region may fire when it recognizes the hook in a letter J while a different area will fire when it recognizes the horizontal base of the letter L for example. Regions in the next stage will fire based on activity in the regions in the stage below. If the lower areas representing the hook from a J and the stalk from a J are active, the corresponding region in the higher stage will fire. This process continues upwards until the stage where the original object is reassembled and the neural region that fires represents the object itself, a J in this case.
“Humans do a rough categorization of objects very quickly,” co-author Charles E. Connor said in the Johns Hopkins press release. “For instance, in just a tenth of a second, we can recognize whether something we see is an animal or not. Our results show that this immediate, rough impression probably depends on recognizing just one or more individual parts of what we see. Fine discriminations – such as recognizing individual faces – take longer to happen, and our study suggests that this delay depends upon emerging signals for combinations of shape fragments. In a sense, the brain has to construct an internal representation of an object from disparate pieces.”
The report appeared in the January 5th issue of Neuron.
Read the full Johns Hopkins press release: “In the Mind’s Eye: How the Brain Makes a Whole out of Parts“