Chap2-Intro2Design
Contents
Chapter 2: Norman’s Design Concepts
In chapter 1 we discussed the 7 principles and associated guidelines for Universal Design. As mentioned in the quote from the Center for Universal Design site, the practice of design goes beyond simply Universal Design principles. Incorporating UD into the process of design ensures that we will be developing sites and digital media which are more effective and usable by as many audiences as possible. However, we also need to know the basic principles of good design. In this chapter we will review basic principles of design as articulated by Donald Norman, a cognitive scientist who has had a significant influence on the design of both objects in the physical world and the digital environment.
Affordance, Constraints, Feedback, Visibility
In this chapter we will discuss concepts such as affordances, constraints, feedback and visibility. These concepts are based on research that began in the latter half of the 20th century on how human beings interact with and perceive the operation of devices, objects and interfaces. Key to this complex of concepts and ideas is the notion of affordance – “a property in which the physical characteristics of an object or environment influence its function.” For example, a door knob is designed for hand gripping and pulling, thus it affords pulling; the flat horizontal surface of a chair with a flat backrest affords sitting. In good design, the affordance of an object or interface matches its intended function. In poor design, there is a discrepancy between the affordance of an object or device and its intended use.
Perceived Affordance
Although Norman did not coin the word nor originate the concept of “affordance,” he is credited with introducing the concept of “perceived affordance” – i.e. how users interpret and perceive the function of a device. The distinction is subtle. In effective design, the affordance not only matches the intended function, but the affordance is clearly visible to the user.
Most of the time, at least for simple objects (e.g. a pencil, a hammer, scissors), we are not conscious of the cues a device relays to us – this usually indicates sound design. If we have to think about how to operate a device, it usually means that its “perceived affordance” is not clearly visible to the user or that the affordance of the device does not match its function. The concept of affordance also applies to electronic devices and computer interfaces. Later in this chapter we will discuss how web pages can either reveal correct cues for operation or misinform the user.
In the later editions of DOET, Norman shares how readers have sent him numerous examples of “Norman Doors” or “Norman devices.” These are doors or devices whose affordances communicate the wrong cues for operation. For example, a handle on a door that communicates pulling when pushing is required or a door handle designed for pulling with a wide flat design that signals pushing because of its shape (see example below). [Norman has an example on page 89].
Constraints
Constraints limit the actions of users in order to prevent error and the wrong use of a device. In contrast to affordance which cues users towards certain operations, constraints limit a system’s options in order to prevent error, damage to the device or harm to the user or others. Through limitations, constraints guide the user towards correct operation or use of a system. Using some automotive examples, constraints include the inability to remove a key from a car ignition until the transmission is in “park” and the engine shut off; the inability to switch the transmission into reverse while the car is moving forward; and the auditory chime when we try to exit the car with the key still in the ignition.
Different design theorists categorize areas of constraints varyingly. Lidwell, Holden and Butler in Universal Principles of Design divide constraints into two categories: physical and psychological. The authors subdivide physical constraints into 3 areas: paths, axes, and barriers. Examples would include, respectively, the rails on the old style credit card swipes (see below) or the grooves on a table saw (see below); a manual egg beater or windmill; and in the computer realm, the boundary of a computer screen.
Norman, whose The Design of Everyday Things, is considered the seminal work on psychological constraints classifies psychological constraints among 3 categories: semantic, cultural, and logical. All other constraints fall under physical constraints in his model. We will now review Norman’s discussion of these 4 categories of constraints.
[sidebar:] A Lack of Proper Constraints can be Fatal [Example of medical radiation device that allowed settings that would emit a fatal dose of radiation].
Physical Constraints The first two automotive examples provided above are representative of physical constraints: cars are designed with the physical properties to prevent shifting in reverse while the car is moving forward and to prevent the key from being pulled from the ignition while the car is running or not in park (for an automatic transmission).
