Psychology Archives

February 7, 2006

Persistance of Vision

I was a judge at my son's science fair this last weekend. Besides being treated to a description of how an 8 year old could tell that rats prefer peanut butter to cheese because the rat caught in the peanut butter trap had bled more - implying it had got there first, there are some interesting results. Sometimes they are things which you already know, but are happy to get confirmation of (the laws of physics still apply), sometimes they are things you weren't sure of but are nice to know in case you are caught in a tough situation (a longer sling on a catapult will fling a baseball further) sometimes they remind you that constructing the experiment to get valid results is the difficult part (though seeing sparks fly is always good fun) sometimes you see that the data is ignored in favor of the desired results (one kid threw out the unexpectedly high tensile strength found in a sample of fishing line as he thought it was too high) and sometimes they make you think about what you take for granted.

This last one was demonstrated by an experiment where one of the kids put a sign in the street telling people to go slow and measured the speeds of the cars with and without this sign. To get good data they did it three days and found that on their residential street it reduced the speed of cars by an average of 4 mph. This brought the speed of the cars from somewhere just over the speed limit to just under the speed limit.

But looking closer disclosed something else. If you looked at the data for the second and third days you would see that there was a much smaller (or even non-existant - I was just eyeballing this so it was hard to tell exactly) drop in speed due to the presence of the sign.

So rather than the claimed 4MPH drop, there was really a BIG drop on the first day and NO drop on subsequent days. Assuming that residential traffic consists of a small consistant group of travelers it pointed out to me that the sign was only effective the first time people saw it. After that it had become just part of the landscape and was ignored.

The lessons from here for scheduling or project management are clear. If you want something to stand out and take action, do it strongly and infrequently.Change the way you present your message so that it is novel and interesting.

If you look, you can sometimes find a corollary to a principle. In this case the evil corollary is that if you want to hide something, hide it in plain sight. Cry wolf every week and people will stop bothering you about why your project is in trouble. They just won't see it any more. Boredom is the friend of the failing project.

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