So, we've just talked about why it's important to evaluate design solutions. We also looked at some of the methods which can involve users, customers, experts, or other stakeholders. No matter what method is used, the most important lesson is to break design solutions as early and as often as possible. This ensures that we come up with a better solution at the end. Now, we'll take a look at commonly used design principles. Having a good understanding of those principles allows us to assess whether a design solution follows or violates any of the principles. Okay, let's get started. The principles we'll cover are affordances, constraints, mapping, consistency, and feedback. They're loosely based on Donald Norman's great book, "The Design of Everyday Things", which was first published in 1988. But it is still very relevant. I highly recommend it to anyone who is interested in design. It's easy to read and full of great examples backed up by Norman's background in cognitive psychology. Let's take a look at the first principle, affordance. Norman describes affordance as the perceived and actual properties of an object that determine just how the thing could possibly be used. What does that mean? It means you look at an object and by looking at an object, you know how to use it. So, the chair you might be sitting on right now for example, the physical properties of the chair tell you how to use the chair. It's clear how to sit down, whether you can move it around easily, whether it can be folded up, and so on. You can even develop a mental model of how to operate the chair without actually physically sitting down on it. If we look at the push button as another example, this very clearly looks like a button, right? We don't have to use the button in order to understand how it works. It looks like a button. So the physical properties, the affordance of this object make it really clear how to use it. Similarly, a well-designed knob clearly communicates its functionality and use. The physical characteristics of the knob tell us how we can interact with it and that it might control something like the volume on the radio. The principle of affordance is therefore really powerful because it allows us essentially to interact with the world around us. At the same time, if an object or interface is not designed well, it's not clear how to use it. Let's look at a specific example. You will most likely be familiar with this kind of device found at pedestrian traffic lights. It allows pedestrians to register their presence through pushing a button, letting the traffic light know that someone is waiting to cross the road. Then it will activate the green light in the next cycle. This particular example here is a photo I took of a traffic push button in Vienna. Which element in this example do you think is a push button? Is it a circle element on the top or the rectangle element on the bottom? Let's take a look at whether your guess was right. Here you go. This little label shows us the answer. The circular shape is the button. If you thought the rectangle element was the button, you weren't wrong. It does look like a button. It has the affordance of a button, but it's not a button. It's a feedback light that goes on once someone pushes the button. The fact that the manufacturer had to attach a label is a great demonstration of this being a failed design. It's not a complex device. It has one button and one feedback light. It shouldn't need a label for us to understand how to operate this device. Here is another example of a traffic light push button. It's the model commonly used in Australia. It was actually designed by an industrial design office here in Sydney and has won several awards. It's button has a very clearly designed affordance. The flat circular button in the previous example was chosen because of its weather resistant features. It prevents rain and moisture from getting inside the device. The device used in Australia gets around this by waterproofing the components internally. As designers, you will always face the challenge of having to balance requirements and technological limitations with functionality. The designer's role is to understand the requirements, to understand the technological limitations, and then to ensure that the design solution doesn't compromise the usability of the product or interface. Doors and door handles sometimes often poor affordance. Norman gives lots of great examples of doors in his book. Pay attention next time you're using a door handle. Does it encourage pushing, pulling, or sliding? The principle of affordance is also applicable in digital user interfaces like websites, mobile apps, and other software applications. For example, buttons in software applications are designed to have a visual affordance. Applying affordance helps users to understand how to operate the application. Let's look at the next principle, constraints. In developing design solutions, constraints need to be considered in order to reduce the number of possible actions and to avoid selecting invalid options. This is really important because if we select an invalid option, in the best case, this leads to an error message, which is frustrating. In the worst case, it might lead to fatal errors in operating a machine such as an airplane or a medical device. Constraints therefore help us to ensure that there is as little chance as possible for the users to make errors. There are different types of constraints, which are logical, cultural, and physical. Let's take a look at the different types. Logical constraints draw on our knowledge of how things logically work. For example, if you turn a screwdriver clockwise, the screw goes in, anti-clockwise, the screw comes out. Cultural constrains draw on things that we learned from growing up in a specific environment. For example, we know that in countries where cars drive on the right side of the road, we have to turn right when getting into a round about. Physical constraints are the most common type used in design. They're also referred to as "poka-yoke", which is Japanese and stands for error proof. The poka-yoke principle was invented at Toyota and applied in the design of their cars. For example, you are unable to take the key out of the ignition until the gear is in parking position. This prevents users from making errors by limiting the number of possible physical actions. Let's look at some examples. These old floppy disks offer a clever design, as a physical form only made it possible to insert a disk exactly one way into the floppy drive. Designing the affordance of an object can support the presence of physical constraints. For example, a key that has a clear visual affordance is easy to use, as it is obvious from just looking at it how it should be inserted into a lock. The opposite is the case as well. If an object offers a poor visual affordance, then the physical constraints are also less helpful in operating the device. We frequently try to insert USB sticks the wrong way because the correct direction is not evident from its physical design. Again, we can translate this principle also into software. For example, physical constraints are used for date selection fields to avoid the entry of an invalidate date. This brings us to the next principle, which is mapping. It is used to describe the relationship between control elements and their effects in the real world. A simple example that is very powerful and has been successful over a long period of time is the steering wheel used in cars. You turn the steering wheel right, and the car goes right. You turn it left, and it goes left. Were steering wheels always of that shape or, did the first cars use a different control mechanism? The first cars used the principle of horse carriages and had two levers. If you're pulling two leavers which steer the car left and right, which wasn't a very clear use of mapping. The steering wheel in comparison offers a much more intuitive mapping, making it easier to operate cars, which is why cars are still using it. Mapping is also used in things like volume and brightness. If you have used a TV remote control where it wasn't clear which buttons control the channel and which one is the volume, then that's possibly because the mapping wasn't very clear. Mapping can also be found in the design of lift buttons, which are commonly aligned vertically to match the levels of the building. If that alignment is violated, it becomes more difficult to operate the lift, like in this example where the buttons seem out of order. This could be especially difficult for someone with vision impairment, who might have to rely on counting the buttons to find the right selection. The next principle, consistency ensures that once we learn how to operate an interface, we can apply the same to another interface. Common examples here are things like shortcut operations in software applications. We know that if in one application, Control-O, opens a document, then we can use the same shortcut in any other software as well. The final principle is feedback, which is a mechanism to provide users with information about the result of an action. Feedback shows that an action has been executed correctly or if there was an error. Feedback is also used to show what the current status is of the interface and which operations are possible, which is also known as feed-forward. Feedback can be delivered through things like sound, highlighting, and animation. So, again, taking lifts as an example, they use feedback to indicate when a button has been pressed, the current position of the lift, and sometimes, also sound to indicate when it arrives. Designing feedback in software applications is critical as it communicates what the outcome of our actions are. Almost every interaction in the software application triggers some form of feedback. The best feedback is the one that we barely notice. Well-designed feedback shouldn't be in our away or distract us from our main tasks but support our interactions. Feed-forward in soft applications is used to let us know what will happen even before triggering an action. For example, well-designed button labels make it clear what is going to happen after clicking the button to submit a form or whatever action is linked to the button. So, we've looked at affordances, constraints, mapping, consistency, and feedback. Considering all these principles in the design of products, services, and systems ensures that it will be easier to use. The principles allow us to form a mental model of how a product, service, or system works. They can also be used to assess existing design solutions, as I've done in the examples in this video. We can assess the effectiveness of the design of objects by testing whether it follows those principles. Next, we'll be looking at different approaches to testing designs used in the industry.
