Scientists have found that people tend to overestimate an incoming object's trajectory and assume an object will miss them, even when it will actually smack them on the head. Since it's important to accurately and precisely perceive movement, it's odd that humans have this error in estimating 3D motion. To figure out where this error comes from, Andrew Welchman, Judith Lam, and Heinrich Bülthoff broke down visual perception into lateral and depth motion to examine how well ten observers perceived these two components of 3D motion.
The researchers asked the observers to judge the distances of objects that were moving laterally (side to side) or in depth (coming straight at the observer). The observers were 1.5 to 3 times better at judging the distance of lateral movement compared to depth movement. Then, the observers compared the speed of small targets that were either moving toward them or laterally. It turned out that the observers estimated the motion-in-depth to be slower than its actual speed. So, if one objectwas moving laterally at the same speed as one thatwas moving toward them, the observers felt that the incoming target was slower.
Why do peopleappear to be more reliable at discerning lateral motions than approaching ones? Other research groups have found that there are larger retinal excursions when people are monitoring lateral motion. There is also a background noise reduction capability that is inherent to binocularvision when applied to lateral movements, which adds to the precision of detection. Thus, there is a strong indication that the faulty perception simply comes from difficulties in seeing depth motion.
Thankfully, even though humans have a knack for miscalculating trajectories of objects that are flying at them, experience does teach people to calibrate their senses to prevent painful injuries. The authors suggest that's why we tend to overcompensate and react in haste to avoid being hit even in situations where we're unlikely to be struck. It could be possible that our estimation inaccuracy has taught us to err on the safe side and just jump out of the way.
Proceedings of the National Academy of Sciences, 2008. DOI: 10.1073/pnas.0804378105