Cognitive load explanation
By Horacio M Pace-Bedetti, PhD, Principal Human Factors Engineer
Question this answers
Why is managing cognitive load critical in medical device design?
Cognitive load is the mental effort required to operate a device. Working memory holds only three to five items, and exceeding this capacity leads to overload and mistakes. High cognitive load causes eighty per cent of medical device user errors. Designers reduce this risk by removing unnecessary steps, simplifying instructions, and providing clear visual cues.
Cognitive load is one of those Human Factors concepts that often gets discussed but not always well understood in medical device development.
At its core, cognitive load is the mental effort required to use a device. When a user is learning something new, interpreting information quickly, or monitoring multiple things at once, that effort builds up fast.
Research consistently shows that when the cognitive load is too high, whether from learning something new, interpreting information quickly, or monitoring multiple things at once, errors increase. In fact, a 2019 study in Nurse Leader Journal found that cognitive overload is a cause in 80% of medical device user errors and distraction plays a role in nearly 75% of medical errors.
I have seen interfaces that seem clear in a design meeting but overwhelm real users when even a mild distraction is added. Add alarms, blinking indicators, or unclear symbols, and the load ramps up quickly. That is when users start missing steps, skipping checks, or making the kind of errors nobody predicted in the early design phase. Both, FDA guidance and IEC 62366-1 emphasize the need to identify and mitigate use-related risks tied to cognitive demands, especially for critical tasks.
Human Factors aims to lower that load. Remove unnecessary steps, reduce complex instructions, use clear visual cues, and make sure information is presented just when it is needed and not all at once. Cognitive Load Theory (CLT) tells us that working memory has a limited capacity. In fact, a 2024 study in JMIR Medical Informatics found that working memory can keep 3 to 5 items in mind at a time and that exceeding this capacity leads to cognitive overload and errors.
When we talk about usability, we are talking about designing for the reality of how people process information, not for ideal conditions. If you can design your device so users do not have to remember too much, read too much, or make too many decisions at once, you are directly lowering cognitive load and reducing risk.
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