A man helping a research participant from behind a counter suddenly drops behind the counter and is replaced by another man. In most cases, the research participant does not notice that the person is different, a phenomenon known as

This is phenomenon known as 'Inattentional Blindness.

Explanation:

Before research, people often believed if you had your eyes open, you were seeing. But it has come to our attention that actually seeing involves a lot more: our sight and memory are attention driven. We need to pay attention in order to remember or to even see. Many studies have meen made and some conclusions drawn: people respond better to stimuli that is meaningful to them. In this example, the research participant is looking for an answer, for help from behind the counter. This is a objective-driven person that wants to get the help needed, the facial details of the person behind the counter may slip. The fact that the facial recognition failed once this person changed supports the idea of inattentional blindness.