The art of thinking · 2 · Perception and attention

Inattentional blindness

Also known as: Perceptual blindness, Invisible gorilla effect

German: Unaufmerksamkeitsblindheit

In cognitive psychology, inattentional blindness is the failure to notice a fully visible but unexpected object or event while attention is engaged in another task, even when the person looks directly at it.

Cognitive psychology
Attention
Perception

In one sentence

Inattentional blindness is failing to notice a visible but unexpected object while attention is on another task (Mack and Rock 1998; Simons and Chabris 1999).

Example

A technician concentrating on the torque values in a maintenance step does not notice a newly added yellow box on the same page announcing a changed lubricant.

What the research shows

Arien Mack and Irvin Rock (1998) named the phenomenon after experiments in which observers judging the arms of a briefly shown cross often failed to report an unexpected shape shown at the same time. Daniel J. Simons and Christopher F. Chabris (1999) showed it for dynamic events: observers counting passes in a basketball video frequently failed to notice a person in a gorilla costume walking through the scene; noticing depended on how similar the unexpected object was to the attended items and on how demanding the task was. Trafton Drew, Melissa L.-H. Võ and Jeremy M. Wolfe (2013) inserted a gorilla image into a lung CT scan: 83 percent of 24 radiologists searching for nodules did not see it, and eye tracking showed that most of those who missed it had looked at its location.

Evidence status

Inattentional blindness is one of the most robustly replicated findings in attention research, in the laboratory and in real-world settings. Rates of missing vary widely with the task, the expectation and the unexpected object, so no fixed percentage applies in general. Expertise does not protect against it outside the expert's search template. The finding concerns unexpected events; it does not mean that people miss everything outside their focus.

How it applies

A warning or a changed value can be visible on a page or screen and still not be seen, because the reader's attention is on the task. The glossary “Applied cognitive psychology for information use” takes this up under warning habituation and hazard perception. Visibility of a warning message is therefore not proof that it was noticed — evaluation with readers checks that — and no wording replaces the protective measures of the risk assessment.

External references

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