Inattentional blindness is the failure to mentally process a stimulus that is in clear view, leaving the observer without any awareness of the stimulus. It is a psychological lack of attention that typically happens when other tasks demanding attention are being performed.
When performing any task requiring attention, we are all prone to miss or ignore other things that happen right in front of us.In 2001, a submarine commander looked through the periscope and saw no ships nearby, and then rapidly surfaced only to crash into the ship which was directly overhead (overturning the ship). Such occurrences are common, and are an important part of many visual illusions and magical tricks. Inattentional blindness is the reason that driving while speaking on a mobile phone is so dangerous – although you may have your eyes on the road ahead, your attention will be elsewhere, leaving you blind to many things that happen around you.
This is why it is so difficult to capture the attention of someone who is is focused on a task. The best way is often to do something very different or unexpected, but there are many times that this will not work (an important lesson for brand advertising). When people are focused on a particular goal, being different may actually make it less likely that you are noticed as many will be functionally blind to anything not directly related to their task. That’s why they are ignoring your advertising or fantastic new packaging. In such situations, the best chance of getting noticed is to signal that you are relevant to their current goal (by using category standard packaging formats and colours which have more chance of being noticed than ‘different’ but unfamiliar designs).
Inattentional blindness is an important design consideration when attention is important, in contexts such as security, safety, product design, retail and advertising. The best strategy is often to create or alter tasks to get attention on desirable outcomes and objects (for example, by providing a coupon ahead of a visit to a retail outlet). If you need to switch attention from one thing to another similar thing, the most effective approaches are to use stimuli with the same meaning, change sensory modality, use faces or personal names (which are good at getting attention) or use a stimuli which represents a threat (but use it carefully).
You can read more on invisible gorillas at InspectorInsight.
Universal Principles of Design by Lidwell, Holden & Butler
The Invisible Gorilla by Daniel Simons & Christopher Chabris