Answer:
The researchers were studying change blindness.
Explanation:
In the "door study", participants were exposed to major visual changes. They would be giving a man directions when two other men walked between them carrying a door. At this moment, the original man asking for directions would walk away carrying the door while another man replaced him. Approximately 50% of participants did not notice the replacement. That phenomenon is called change blindness, and it usually takes place when a person's attention is not focused on visual details. Since the participants in the study were more concerned with giving directions than with their interlocutor's appearance, they wouldn't notice the change.
