Inattentional Blindness

Posted by Albert Gareev on Nov 02, 2010 | Categories: LinksNotes

Last week I asked QuickTestingTips readers to share examples of Bounded Awareness they observed in their work, and here I’m with my stories.

Let’s start with this video. You see two teams of people playing basketball. While you watch the video, count number of passes made by the each team.

Link to the video

Link opens a third-party web-site. Video and image copyright: Daniel J. Simons

..Now, after you’re done, list what else looking unusual you noticed while watching the game. Try to do that without replaying the video. (And I’ll give you a hint at the end of the blog post*.)

In the experiments, like this one,  an observer needs to concentrate on one cognitive task, and, sometimes, fails to notice an unexpected and/or unrelated event.

That’s what Inattentional Blindness is.

Inattentional Blindness in Software Testing

I begin list of the examples with the most obvious one, which I’ve observed many times.

Driven by Testing Procedures

Test Cases, as step-by-step execution instructions, require attention themselves, and the more detailed a test case is the more focus it draws away from the system under test.  That is – increasing the chance to miss a real problem. The factor of distraction is even greater if testers have to follow a test reporting procedure.

So, if you face common arguments, like “testers must be multi-tasking” or “testers must always pay attention to detail” address them with a scientific proof.

On the other hand, you can counter such an approach by pointing out to the poor level of confidence that a limited set of static checks can give.


People tend to avoid consciously reading long solid texts. They do screening instead, jumping from one keyword to another. While this is helpful in processing large volumes of information, screening used as the only method means missing critical information.

As a particular example, I recall a major problem found by a colleague of mine in one of the projects I worked. More by a chance, rather intentionally she noticed that date stamp in a log file for a certain entry showed next date, and that was for a batch job supposed to be processed within a few hours overnight! This problem successfully escaped attention of many people because time part of the stamp was still showing acceptable night time, and the message, that everyone looked for, was usual “processing done successfully”. 

Now, this a good occasion to say: be very careful if you’re delegating judgment to automation.

And a perfect occasion to cite James Bach: question everything.

* Hint: what color was the umbrella?

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This work by Albert Gareev is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported.