Conceptual Model and Water Tap story


Conceptual model is part of the communication process between product designer and the audience who use the product. It plays a critical role in the discoverability of the product, or in other word, whether or not people can know how to use its functions.

Conceptual Model

“A conceptual model is an explanation, usually highly simplified, of how something works. It doesn’t have to be complete or even accurate as long as it is helpful.” - Don Norman, Design of Everyday Thing

The trash icon you see on a computer screen help people create the conceptual model of where people can delete data inside the computer. Trash bin inside the computer and a clock inside mobile phone are effective conceptual models that help people understand the functionalities of products.

Mental Model

Mental model, as its name implies, is conceptual model perceived by people. It is defined well by Susan Carey’s 1986 article “Cognitive Science and Science Education”:

“A mental model represents a person’s thought process for how something works (i.e., a person’s understanding of the surrounding world). Mental models are based on incomplete facts, past experiences, and even intuitive perceptions. They help shape actions and behaviour, influence what people to in complicated situations, and define how people approach and solve problems.”

There are a few key takeaway points about mental model taken from 100 Things Every Presenter Needs To Know About People

  • People always have a mental model
  • People get their mental models from past experience
  • Not everyone has the same mental model
  • The more you understand people’s mental models about your design, the better you are able to craft a more usable product.

How to match conceptual model and mental model

Usually the device it self contains elements that communicate the conceptual model. People understand the conceptual model by reading manual, talking with people who have used it, or relating to their past experience. The major clues to how things work come from their perceived structure - in particular from signifiers, affordances, constraints, and mapping.

“For everyday things, conceptual models need not be very complex. After all, scissors, pens, and light switches are pretty simple devices. There is not need to understand the underlying physics or chemistry of each device we own, just the relationship between the controls and the outcomes.” - Don Norman, Design of Everyday things, page 28.

The matching of conceptual model and mental model is addressed in discoverability.

According to Cennydd Bowles in Shades of Discoverability, there are three ways of how to communicate functions:

  • Explicit cues
  • Implicit cues
  • Discovery through use

In this article, I want to discuss explicit cues which, in my opinion, sometimes cause trouble for people in daily life.

Explicit cues are guides and instructions given directly. They can be post-it notes on devices telling you how to do certain things, follow certain steps. They are written and clear to people. However, they are intrusive into the experience since instruction can be hard to remember, people need to memorise or need to see the note whenever they want to use and therefore, need longer time to build new habits. Explicit cues are often used as a quick solution to reminding people of certain new functions of devices in daily usage. You may see that at microwave, coffee machine, door, toilet.

Case Study: Water Tap

At my old office pantry, there is a water tap. When the office manager wanted to setup the hot water dispenser, the technician installed a small tube dividing the water flow coming out from the tap. The original tap controlled the water both to the new hot water dispenser and the usual output. Therefore, after that, they installed another tap to control the water flow to the sink only, requiring the original tap to be always open since the dispenser need constant input of water.

Pantryat my office

The tube from water tap to hot water dispenser

In order to take water, we started using the new tap. Some people tended to forget that. So we put a note on each water tap. Post-it notes are explicit cues, signifying a new function and usage behaviour. For me, seeing the note didn’t help because I always followed old habit and tend to forget that note. It took me days to get used to the new way of getting water.

Original tap

New tap

Principles of Design for Discoverability

In summary, principles of design for discoverability are:

  • Provide a good conceptual model
  • Make things visible (signifier, affordance)

Together with explicit cues, we can use implicit cues to help solve this usability problem. “The shape, texture, alignment, or another visual property of the element at rest helps to suggest its function”. This is what Don Norman terms “affordance”. The original tap can be redesigned to signify its new function. We can cover it with a dark colour cloth to make it look very hard to use, communicating with people that they shouldn’t use this, and instead, use a new one.

With new interfaces and new devices coming out in technology market, discoverability has become a common topic to be addressed. It is essential for designer to understand people’s knowledge and past experience to choose the appropriate communication method so that the product will convey the right conceptual model to people.

This article was originally published in January 2015 on my previous website.