Look a little closer
A fully visible object can go unnoticed when attention is concentrated elsewhere. This is not poor eyesight but inattentional blindness: limited attention fails to select unexpected information for awareness.
In a famous experiment, participants watched two teams pass basketballs and counted passes by one team. A person in a gorilla suit crossed the center of the scene, yet many viewers did not report noticing it while performing the task.
The result seems strange only if vision records every part of a scene equally. The brain prioritizes objects and events relevant to a current goal. While protecting the pass count, an unexpected object may stimulate the eyes without reaching conscious report.
Detection is not determined only by an object's size. Similarity to attended objects, difficulty of the main task, expectations and motion all alter the likelihood that an unexpected event will be noticed.
The phenomenon does not mean people are always oblivious or that someone who missed the gorilla is dishonest. The same observer may notice completely different parts of a scene when given a different goal.
In driving, medical imaging and security monitoring, it is risky to assume that visible means noticed. Checklists, rotating roles and independent review can recover information that fell outside one person's attentional set.
