Final answer:
Inattentional blindness is a psychological phenomenon where a person fails to notice a visible but unexpected object because their attention is concentrated on another task, and is particularly related to the perceived urgency of that primary task.
Step-by-step explanation:
Inattentional blindness is the failure to notice a fully visible but unexpected object because attention is engaged on another task or aspect of the environment. The phenomenon can be related to the perceived urgency of the primary task. When individuals are intensely focused on a primary task, such as counting the number of times a basketball is passed between players, they may completely miss other unexpected but salient events, like the appearance of a person in a gorilla costume among the players. This is demonstrated in the classic study by Daniel Simons and Christopher Chabris. The urgency or complexity of the primary task can monopolize attention, leading people to overlook other stimuli, a concept supported by experiments involving participants who failed to notice a red cross on a screen when they were instructed to focus on black or white figures.