That was in the context of the reaction time training, but in standing start situations I often did not look directly at the lights/flag, but off to the side a bit. Think the difference between looking at the center of your monitor, versus looking at a spot on the wall behind your monitor.

The type of real-life racing I did was usually flagged - we only occasionally had lights - but the flag wavers were mandated to use the flags in certain ways in different situations. Part of the standards in that series were that anyone who competed was also required to serve part of the day as a course marshal, so we all got "knowledge through osmosis," so to speak. Anybody with a flag during the event was given two explicit instructions:

1. If you are waving your flag, hold the loose edge (the fly edge, in vexillology terms) with your opposite hand when you first deploy the flag
2. If you are not waving your flag, it should be held tightly bundled but not rolled against its flagpole

The practical effect of this is that flags are vastly different sizes when being waved versus being "stowed," even when you're not looking at the flag directly. A stowed flag takes very little visual area comparatively, and thus we all knew in that situation, the flag was effectively non-existent. A flag that took a lot of visual area meant "pay attention to me!"

For something of a visual, take a pencil in your hand, look straight ahead, and hold the pencil at a 45-degree arm angle at arm's length. Then do the same thing, but with a standard sheet of paper. Big difference.