How is visual information processed in the brain

The Debatable Dress. Turning Wheel Illusion. Trending Popular articles on BrainFacts. The Neuron. Proteins That Balance Our Moods. Like Subscribe Follow Follow Subscribe. About BrainFacts. The neural mechanisms of visual perception offer rich insight into how the brain handles such computationally complex situations. Visual perception begins as soon as the eye focuses light onto the retina, where it is absorbed by a layer of photoreceptor cells.

These cells convert light into electrochemical signals, and are divided into two types, rods and cones, named for their shape. Rod cells are responsible for our night vision, and respond well to dim light. Rods are found mostly in the peripheral regions of the retina, so most people will find that they can see better at night if they focus their gaze just off to the side of whatever they are observing. Cone cells are concentrated in a central region of the retina called the fovea; they are responsible for high acuity tasks like reading, and also for color vision.

Cones can be subcategorized into three types, depending on how they respond to red, green, and blue light. In combination, these three cone types enable us to perceive color. Signals from the photoreceptor cells pass through a network of interneurons in the second layer of the retina to ganglion cells in the third layer. The neurons in these two retinal layers exhibit complex receptive fields that enable them to detect contrast changes within an image; these changes might indicate edges or shadows.

Ganglion cells gather this information along with other information about color, and send their output into the brain through the optic nerve. All neurons within a column respond preferentially to bars of a specific orientation, denoted here by colour.

Moving up the visual hierarchy, neurons represent more complex visual features. For example, in V2, the next area up in the hierarchy, neurons respond to contours, textures, and the location of something in either the foreground or background. Beyond V1 and V2, the pathways carrying What and Where information split into distinct brain regions. At the top of the What hierarchy is inferior temporal IT cortex, which represents complete objects — there is even a part of IT, called the fusiform face area, which specifically responds to faces.

The top regions in the Where stream are involved in tasks like guiding eye movements saccades using working memory , and integrating our vision with our body position e. In summary, the visual cortex shows a clear hierarchical arrangement.

In lower areas those closest to incoming light, like V1 , neurons respond to simple visual features. As the visual input works its way up the hierarchy, these simple features are combined to create more complex features, until at the top of the hierarchy, neurons can represent complete visual objects such as a face. Such a ' bottom-up ' approach would be far too slow and laborious, but more importantly, it would render our visual world full of ambiguity and we would struggle to survive.

Instead, our perception relies to a very large extent on our previous experience and other ' top-down ' mechanisms such as attention. QBI Professors Jason Mattingley and Stephen Williams are both studying how attention can alter visual processing, using cognitive and cellular approaches, respectively.

Square A looks lighter, but is actually darker than square B. Clearly, our visual system is doing a terrible job at seeing reality. Professor Sur said this is a very important concept in understanding the brain, because from merely an anatomical or structural study of the brain, different areas of the cortex look remarkably similar.

What distinguishes the different areas of cortex is the inputs they get and how these inputs get processed and then farmed out to different areas. Massachusetts Institute of Technology. Search MIT. Search websites, locations, and people. Enter keywords to search for news articles: Submit. Browse By. Publication Date :. Press Inquiries. Press Contact : Elizabeth A.