Fig. 1.

Someone in the car on the left would view a tractor or a bell tower differently than when the car is on the right: that is, angle β is smaller than α, an example of parallax. If the car moved from left to right, the nearby tractor is likely to be perceived as moving faster past the car than the far-away bell tower, an example of motion parallax. With a focus point, near sources appear to move in a direction opposite that of the observer compared with far sources. And, near sources might occlude far sources when the observer is in one positon (Left) compared with another position (Right). If the sources only produced sound and could not be seen, then only motion parallax is likely to provide depth/distance information.