Anecdote time: While teaching high school students to use a stop watch to make physic experimens, most of them have a 20ms error. But one of them had a 5ms error. At firts I though he was lying, becuase it's commont to make up numbers intead of using the watch, but it's difficult to make up numbers unless you know statistics. So I talked to him and watched he redo the experiments. He had a 5ms error!
The research, published in Plos One, found that some people reported a light source as constant when it was in fact flashing about 35 times a second, while others could still detect flashes at rates of greater than 60 times a second.