Turning heads is no problem for the brain
Visual cues play an important role in correcting for the effects of eye and head rotations.
When strolling along a path beside a busy street, we can look around without losing our stride. The things we see change as we walk forward, and our view also changes if we turn our head — for example, to look at a passing car. Nevertheless, we can still tell that we are walking in a straight line because our brain is able to compute the direction in which we are heading by discounting the visual changes caused by rotating our head or eyes.
It remains unclear how the brain gets the information about head and eye movements that it would need to be able to do this. Many researchers had proposed that the brain estimates these rotations by using a copy of the neural signals that are sent to the muscles to move the eyes or head. However, it is possible that the brain can estimate head and eye rotations by directly analyzing the visual information from the eyes. One region of the brain that may contribute to this process is the ventral intraparietal area or ‘area VIP’ for short.
Adhira Sunkara and colleagues devised an experiment that can help distinguish the effects of visual cues from copies of neural signals sent to the muscles during eye rotations. This involved training monkeys to look at a 3D display of moving dots, which gives the impression of moving through space. Sunkara and colleagues then measured the electrical signals in area VIP either when the monkey moved its eyes (to follow a moving target), or when the display changed to give the monkey the same visual cues as if it had rotated its eyes, when in fact it had not.
Sunkara and colleagues found that the electrical signals recorded in area VIP when the monkey was given the illusion of rotating its eyes were similar to the signals recorded when the monkey actually rotated its eyes. This suggests that visual cues play an important role in correcting for the effects of eye rotations and correctly estimating the direction in which we are heading. Further research into the mechanisms behind this neural process could lead to new vision-based treatments for medical disorders that cause people to have balance problems. Similar research could also help to identify ways to improve navigation in automated vehicles, such as driverless cars.
To find out more
Read the eLife research paper on which this story is based: “Role of visual and non-visual cues in constructing a rotation-invariant representation of heading in parietal cortex” (February 18, 2015).