Mental Models
People interpret an interface through earlier experiences. They do not need to know its implementation to imagine what a control will do.
These expectations can differ and remain incomplete. The product team's mental model does not necessarily represent the model held by the people using it.
What it means
A mental model explains what someone believes about a system, rather than its technical operation. It changes when experience confirms or contradicts those beliefs.
Origin of the concept
The concept belongs to cognitive psychology, which investigates how people represent and interpret situations. In human-computer interaction it helps examine the gap between someone’s explanation and a system’s actual behaviour. Usability literature applies it to expectations and actions; users do not need to understand technical implementation to develop a working model.
Application in UX
Use consistent names and behaviour. When an interaction is unfamiliar, explain its consequence before asking for a decision. Investigate the audience's expectations instead of assuming everyone shares the same ones.
Use research to understand relevant expectations rather than inferring them only from visual conventions. An interview may reveal what saving means to someone; an observed task can show whether they expect confirmation or automatic synchronisation. Expectations can differ between groups and should be compared with the system’s actual behaviour.
Application in ecommerce
Shoppers commonly expect a selected size to remain selected when adding a product to the cart. Changing the variant without notice contradicts that expectation.
Category navigation, baskets and filters create expectations about where products belong and what persists during shopping. If changing a variant resets quantity, the system should explain that behaviour. At checkout, communicating when an order is confirmed prevents a review screen from being mistaken for a completed purchase.
Practical example
Imagine someone choosing a blue T-shirt in size M. The cart should display that combination and allow review. A stock-related change should require a new choice rather than silently substitute the product. This is a hypothetical scenario for reviewing the design.
Common mistakes
Designing exclusively around the business’s internal model produces labels and steps that are difficult to interpret. Another mistake is assuming all shoppers share one model. Avoid changing conventions without explaining the new behaviour, and do not attribute every failure to inattention: the interface may contradict a reasonable expectation.