Given any situation, there are “n” no of sensory inputs (stimuli), which impacts the human mind. To handle such humongous amount of data, the human brain acts as a pattern-processing machine and starts to group them to reduce the load.
It focuses on stimulus, which is important for the User. This is called “Selective Attention”
Example: If you were to look at Yahoo Mail interface …your attention will be primarily on the ‘first mail’ in the inbox slot. (Short Term Memory)
Next, your attention will be on “the left nav” containing the folders list etc., and the “top nav” containing buttons like delete, reply etc. You might not be able to exactly recall the links in the exact order, but then, you do remember some of it. (Long Term Memory)
You also don’t remember “730×90 banners” which is right on top and blinking at you.
You only think about it when you see it. (Working Memory) and forget all about it soon.
And the next time you log it, you mentally block it. This is the basic concept behind “Banner Blindness”.
These huge blinking banners do what is called an “Attention Shift”
Attention shift can be Positive and Negative. When a stimulus shifts the user’s attention from what is important to him, disharmony in interaction happens. This affects performance. No wonder Google’s text only banners are so cool!
In case of alarm systems, both the visual and auditory stimuli shift the user’s attention to what is REALLY important to him.