It's a matter of iconic memory ability. That is, how quickly we can process visual information. For humans it's about 1 second to fully process info.
There also need to be motivation for good performance. It's likely that the chimps were reinforced on a typical VI schedule on something like that. Same tests to get pigeons to peck at a screen.
Thing is, people, chimps, pigeons all have the same capacity for processing visual information. it's just a matter of motivation. Deprive the people of food, and make the reward a cheeseburger, see who wins.