Viewers require about to be able to perceive the gist of a scene.

To be able to understand or perceive what the scene is saying, viewers just need some few seconds or a milliseconds to know the full details. It all depends on the complexity of the scene before it can be attributed to either milliseconds eyes fixation or a few seconds eyes fixation

Explanation:

During the viewers first eye fixation on that scene, the viewer will be able to quickly to know what the scene is all about from a brief eye fixations. Some gist of some scene do take long to get, so it also depends on the Brain but no matter how complex the scene takes is, viewer eyes fixations will still get the meaning of the scene but it might just be longer than the simple scenes. This might require a few seconds eyes fixation

It is known that humans can understand a real world scene quickly and accurately, scanning many times per second while eyes fixation is on a complex scene. Each of these glances carries information. While some scene even requires a few hundred milliseconds eyes fixation by humans and the truth of the scene will be know to the viewers

b - those executed came from every social and economic class