Schneier on Security

Roger • January 1, 2010 6:27 AM

I partially agree with the preceding commenters who were unimpressed.

In fact change blindness researchers have done some remarkable experiments on just how much you can get away with while (most) people don’t notice, and it does have security implications — but this particular example was a little lame. The two test actors were very similar and unremarkable in appearance; very similarly dressed in weak pastel shades which both looked grey in the dim office lighting; and more importantly, the actors were in a situation where most of the subjects were simply not paying any attention to them.

For example, watch the eyes of the girl in the blue t-shirt. She looks at the huge distracting sign above the actor’s head, starts to scan the room (picking up such minute details as the potting medium in the planter) but then focuses on the papers thrust under her nose, and does not make eye contact with either actor until saying “thank-you” to actor no. 2 a moment before leaving. She literally doesn’t look at actor no. 1’s face. The girl in the brown t-shirt glances at actor no. 1’s face very briefly when asking him the date, but not otherwise. (And since she doesn’t know what day it is, she may be a little distracted otherwise!) Two of the men who didn’t notice the change emphasised that they were in a rush; one of them is nervously glancing down the hall (where he wants to go) and in every direction except at the actor, whilst incidentally also adjusting his spectacles which are slipping down his nose: yes, this “change blind” subject is also short-sighted …

[And as a cute aside, whilst reviewing the video to see exactly what each subject did, I finally noticed that Professor Simon’s shirt also changes colour between the first and second scenes of his interview .. very cute gag!!]

The more remarkable security conclusion about this experiment is not that people noticed nothing but gender about a person when they didn’t look at his face. The remarkable thing is that so many apparently educated people signed — without reading — a piece of paper handed to them by an unknown stranger whom they didn’t even look at !!

Near the end, Prof. Simons remarks that is is not known whether particular people have a different likelihood of noticing the change, or if they were just lucky on the day. This would be very interesting information and should be fairly easy to test by simply exposing each test subject to more than one scene change before telling them what was going on. It would also be interesting to quantify the percentage against different types and sizes of changes.

Roger • January 1, 2010 4:58 PM

I also had a look at the Derren Brown video — the one where an actor asks a stranger for directions and is swapped mid-conversation (after being interrupted by a large painting being carried between the actor and the test subject.)

I have to say that on close examination, that video is also less than impressive. Of the subjects that Brown’s editors chose to leave in the show, only one — a highly extroverted person — outright challenges the actor about the substitution. However in nearly all cases, the subject shows some kind of facial indication of consternation, but is simply baffled as to how to react.

For example the second subject — the man with the central European accent — doesn’t openly challenge the substitution, but as he walks away, at 1:03 he subtly checks the contents of his bag. It might be a coincidence, but it looks to me as if he is worried he is being scammed and is checking he hasn’t been pickpocketed. Subject 3 doesn’t remark on the substitution, but stops assisting (she very politely suggests the actor take his enquiry elsewhere, by nominating a person she has obviously picked at random.) Subject 4 is the most highly extroverted and helpful, and openly voices his confusion at the substitution.

Subject 5 superficially appears the most extreme example, as a tall, close cropped white man is substituted by a much shorter Asian woman with a dramatic ponytail, and the subject seems not to notice. However, the subject DOES react: after a moment of speaking to the Asian actor, she looks around and then starts scowling and her tone of voice changes. It seems to me that she thinks the Asian woman is the first actor’s wife or girlfriend, and that she is still speaking to both of them; when she realises the male actor has walked off mid-sentence, she becomes annoyed at his rudeness. I admit this explanation is speculative, but at any rate it is certainly not the case that she doesn’t react.

This video would have been far more impressive if each subject was stopped again slightly further down the street and asked what they thought had just happened. As it stands, all that can be said is that when these people were accosted on the street in a big city, if they noticed something hinky they mostly chose not to verbalise it. But that is neither surprising nor interesting.

Roger • January 4, 2010 6:26 AM

@Patrick G.:

To those people who complain about the test setup … the missing focus on the changed subject/object is exactly what “change blindness” is about.

I don’t believe that’s quite true. The phenomenon of change blindness occurs when someone is viewing the scene that changes and doesn’t notice it. We can get all semantic-ky on what we mean by “viewing”, but it is obviously trivially true that someone will not notice a change in a scene that they are not viewing, so the “phenomenon” becomes trite if it is defined too broadly. It must be defined so that it is in some sense surprising that the change was not noticed.

For example, the dancing gorilla is surprising because we expect that an observer who is closely monitoring the actors would notice a gorilla in their midst. Most people are surprised that the mere act of concentrating on a subset of actors could cause one to not notice a (simulated) large, aggressive animal walking right through your field of view.

On the other hand, the experiment described here is unremarkable because we expect that at least some people pay no attention to — in fact, do not even look at — a minor functionary who hands them a piece of paper. If they don’t even look at him, it is unsurprising that they do not notice his face.