The Traits of Optic Flow

There are many ways in which we view the world. We're able to see from different angles, see different colors and shading, we're able to perceive motion when it technically isn't there, and we're also able to see objects "flow" around us. This last visual phenomena is called optic flow, and refers to the way in which objects around us appear to move. Distant objects, such as the sun, moon, the clouds in the sky, and even a passing airplane appear to move very slowly, while objects closer to us appear to move very quickly (Centeye, N.d). A study by Warren et al. (2001) noted that optic flow plays a significant role in allowing humans "to have robust locomotor control under varying environmental conditions."

One reason why Warren et al. (2001) could have reached these conclusions is an optic flow trait in which objects move relative to our movement. Goldstein (2010) notes that a person's movements provide "information that can be used to guide that movement." For example, turning from right to left brings nearer objects that at first looked further away. Due to optic flow, we're able to see these objects get nearer, and as we walk near them, we see that they also look nearer and that they appear to be approaching faster than background objects. This allows us to steer and direct our bodies (or even vehicles and the like) to avoid hitting he objects, or to interact with them as needed. This same trait of optic flow gives us the sense that we're moving when looking at a screen of things flying toward us (think Disneyland's Star Tours). Although we're sitting in one location, the fact that objects are flying toward us, with the ones nearer appearing to come faster and the back ones appearing to approach slower, it seems as though we're moving through space. It's also interesting to note that while forward movement expands the field of optic flow, backward motion contracts it. This can be seen in basic motion as one walks or drives forwards or backwards.

Another distinguishing trait of optic flow is the fact that objects that are more distant remain more distant when there are nearer objects that appear to be nearing. Goldstein (2010) illustrates this point with a tunnel. The tunnel walls appear to be moving along side us as we walk or run, however, the light at the end of the tunnel appears to remain the same up until the point at which we are very near. This also works with other distant objects like mountains and hills, even a distant tree or house. This allows us to focus on the end goal, but also remain wary of nearby objects which need to be navigated past.

References:

Centeye (N.d). "What is Optic Flow?" Retrieved November 16, 2009, from http://www.centeye.com/pages/techres/opticflow.html

Warren, W.H., Kay, B.A., Zosh W.D., Duchon, A.P., & Sahuc, S. (2001). Optic flow is used to control human walking. Natural Neuroscience, 4(2): 213-6.