visual science


Expert: Suspect Images Clear Now, But Prevention Too Complex A Task

You can’t help but ask: If we can see these clear suspect images shared by the FBI now, couldn’t someone possibly have detected the threat before the fact and headed off all that mayhem?

In short, the answer is no. That is simply too complex a task, beyond our human and current technological capabilities, said Prof. Jeremy Wolfe, a visual attention researcher in the departments of ophthalmology and radiology at Harvard Medical School and Brigham and Women’s Hospital. His take on the challenge:

With all these videocameras all over the place providing a mountain of data, somebody is likely to ask if, given that the signs were all there ahead of time, shouldn’t someone have seen this coming? Sadly, that task is essentially impossible, at least at this point. When you don’t have anything specific to look for or a specific place to look, even though you’ve got all this footage, there’s no way to do it.

For example, imagine this problem: Remember the bombs a few years ago in the London subway? You’ve got video cameras everywhere in the London subway. After the fact, you can see the bomber, carrying a backpack down into the subway and coming out without it. Before the fact, you just don’t have enough humans to look at all that imagery of all the people on the ‘Tube”. Perhaps we could use a computer.

Now imagine trying to create a computer program that will mark everybody as they go into the subway, find them again when they come out of the subway — in a different place, of course — and figure out if they are still carrying their backpack. If you think about that for a moment, you realize that is a monumentally hard problem. And that’s actually a smaller problem than the problem of ‘Is anybody doing anything suspicious in Boston today?’

The problem is still hard, but much more tractable, after the fact. Now you concentrate on a restricted range of time and a very restricted place. This probably still involves quite a lot of footage but we can point human eyeballs at every bit of that footage. We can fast-forward and rewind and turn this from an absolutely impossible search task to really quite a tractable one. It’s going to be difficult but it’s quite a tractable identification task.

In the case of the Boston bombing, you might have a pretty good idea that you’re looking for something like a black nylon bag. When you see it, you back up in time to see when it’s not there. Continue reading