Since it was identified which cells do what for vision, the next question is what part of the brain is in charge of processing visual information? Vision is more complicated than it seems. For the longest time, it was thought that vision was a matter of an image that is cast on the retina and the image is sent to the brain, the way images are recorded on to digital tape with a video camera. The reality is that vision is more like speech, than mere image capture. In order to navigate our world, our brains interpret visual sensory like shape and size and even nonvisual cues, like sound and motion.
Researchers at the National Eye Institute (NEI) found that a brain region in the superior temporal sulcus (fSTS) is vital for processing and making decisions about visual information. While the processing of visual information begins in the eye, the important work starts in the part of the midbrain called the superior colliculus. This area handles sensory input necessary for the brain to notice something going on in the field of vision and to decide whether or not action is needed.
Researchers worked with monkeys trained to do specific visual attention tasks while inside a functional magnetic resonance imaging (fMRI) machine. While staring at a dot straight ahead, the monkeys pay attention or ignore events happening in the periphery, namely a patch of moving dots that change direction to either the right or the left side of their visual field. The part of the monkey’s brain that is triggered when paying attention to this task is the superior colliculus and less so when they are ignoring it.
This was surprising since this part of the brain wasn’t previously known to be important for visual attention. The measurements showed that a large part of the fSTS is dependent on the superior colliculus and the neurons use this information to represent complex visual information. In addition, researchers were surprised to learn that these regions were dependent on input from the midbrain.
The fSTS neurons were activated when monkeys reported seeing an event. When visual events were ignored, the fSTS neurons were quiet. Researchers then dulled the function of the superior colliculus and the fSTS neurons demonstrated less distinction between ignored and attended visual events. That means that the fSTS depends on the superior colliculus to specify which visual events are important and which aren’t.
This has implications for those who have a condition known as visual neglect, which occurs in some people who have had a stroke or other brain injury in areas involved in visual attention. Those with visual neglect can see all the objects and events in their visual field, but they aren’t aware of events on their affected side, especially when the visual field is cluttered. The findings from this research could provide clues to treating visual neglect.
As research often shows there is more to vision than meets the eye. Especially since the brain does the heavy lifting with processing visual information.