The concept of affordances originates from ecological psychology; it was proposed by James Gibson (1977, 1979) to denote action possibilities provided to the actor by the environment. In the late 1980s Norman (1988) suggested that affordances be taken advantage of in design. The suggestion strongly resonated with designers? concern about making possible uses of their products immediately obvious, and soon the concept came to play a central role in interaction design and Human-Computer Interaction (HCI). This chapter discusses the origins, history, and current interpretations of affordances in HCI research, and reflects on the future of affordances as an HCI concept.
44.1 Introduction: Why affordances?
Good designs are intuitive (footnote 1). Take for instance the Holmes stereoscope, designed in the 19th century (Figure 1). You can immediately see that: (a) there is a handle, which you can grasp with either right hand or left hand, (b) you hold the device, so that it is supported from below, (c) you can insert stereo cards (or ?stereoviews?) in a card holder slot, and (d) you can view the cards through a pair of lenses. The shape of the hood surrounding the lenses indicates how exactly the device should be placed for proper viewing.
Even if you haven?t seen a Holmes stereoscope before, you are likely to be able to use it almost immediately.
Courtesy of Victor Kaptelinin. Copyright: CC-Att-ND-3 (Creative Commons Attribution-NoDerivs 3.0 Unported).
Figure 44.1: A Holmes stereoscope
There are myriads of cleverly, intuitively designed things around us, both old and new. Some examples include a car door handle, which we use correctly without thinking, even if we are encountering that particular handle for the first time (Figure 2), a Swiss Army knife (Figure 3), a summer cottage window lock (Figure 4), and so on. The list of things that dutifully and unobtrusively serve us in our daily lives is endless.
Courtesy of Victor Kaptelinin. Copyright: CC-Att-ND-3 (Creative Commons Attribution-NoDerivs 3.0 Unported).
Figure 44.2: Intuitive everyday designs: Car door handles.
Copyright: pd (Public Domain (information that is common property and contains no original authorship)).
Figure 44.3: An intuitive everyday design: Swiss army knife.
Copyright status: Unknown (pending investigation). See section "Exceptions" in the copyright terms below.
Figure 44.4: An intuitive everyday design: Window lock.
However, the design of some of the things we encounter in our daily lives is not exactly intuitive ? and, unfortunately, poorly designed things are not that uncommon. An insightful discussion of a diversity of confusing and frustrating objects, such as doors that may easily turn into traps, can be found in Norman (1988).
Poor designs can even have far-reaching political consequences. Tognazzini (2001) argues that the design of the butterfly ballot used in Palm Beach, Florida, during the 2000 US presidential election, may have tipped the balance of the election as a whole. Arguably, thousands of voters were confused by the design of the ballot and voted for the wrong candidate (see Figure 5).
Copyright: pd (Public Domain (information that is common property and contains no original authorship)).
Figure 44.5: A counterintuitive design: The ?Butterfly ballot?. The Democratic Party is listed second on the left column, but in order to vote for it one should press the third button. Pressing the second button would cast a vote for the Reform Party.
What is the secret of making designs intuitive? As suggested by the examples above, an essential part of it has to do with perception. It is not sufficient for a good design to be rational and logical. Great, intuitive designs are those that allow us directly, and correctly, to see what we can do with a thing.
Direct perception of possibilities for action is, essentially, what the concept of affordance is about. The concept was originally proposed by an American psychologist, James Gibson, to denote what the environment ?offers the animal, what it provides or furnishes, either for good or ill.? (Gibson, 1979). The concept was introduced to the field of design, and eventually HCI, by Donald Norman in his groundbreaking book The Psychology of Everyday Things (1988). Norman defined affordances as:
?? the perceived or actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used? A chair affords (?is for?) support and therefore affords sitting. A chair can also be carried. Glass is for seeing through, and for breaking.? (Norman, 1988).
Affordances, according to Norman, can be fruitfully employed in design:
?Affordances provide strong clues to the operations of things. Plates are for pushing. Knobs are for turning. Slots are for inserting things into. Balls are for throwing or bouncing. When affordances are taken advantage of, the user knows what to do just by looking: no picture, label, or instruction needed.? (Norman, 1988).
The concept of affordances was quickly adopted in HCI and interaction design; it became popular among practitioners, researchers, and educators. For designers of interactive technologies the concept signified the promise of exploiting the power of perception in order to make everyday things more intuitive and, in general, more usable. Affordance is also considered a fundamental concept in HCI research and described as a basic design principle in HCI and interaction design textbooks (e.g., Rogers et al., 2011).
The use of affordance is not limited to the design of physical objects. In fact, the concept has been especially appealing to designers of graphical user interfaces. Compared to traditional industrial designers, user interface designers can more freely and easily define visual properties of the objects they create. Therefore, they appear to be particularly well positioned for providing what Norman (1988) calls ?strong visual clues to the operation of things?. Examples of user interface elements, which provide this kind of strong clues, are clickable(footnote 2) buttons and tabs, draggablesliders, and spinnable controls, as well as other elements that more or less directly suggest suitable user actions (see Figure 6).
Copyright ? EasyChair. All Rights Reserved. Used without permission under the Fair Use Doctrine. See the "Exceptions" section (and subsection "fairUse") of the copyright notice.
Copyright ? Apple Inc. All Rights Reserved. Used without permission under the Fair Use Doctrine. See the "Exceptions" section (and subsection "fairUse") of the copyright notice.
Copyright ? ResRobot. All Rights Reserved. Used without permission under the Fair Use Doctrine. See the "Exceptions" section (and subsection "fairUse") of the copyright notice.
Courtesy of Flickr User Jodiepedia. Copyright: CC-Att-SA (Creative Commons Attribution-ShareAlike 3.0 Unported).
Courtesy of Flickr User l-i-n-k (Thomas Link). Copyright: CC-Att-SA (Creative Commons Attribution-ShareAlike 3.0 Unported).
Figure 44.6: Examples of user interface elements, which directly suggest suitable user actions: (a) clickable button and hyperlinks, (b) draggable sliders, (c) clickable tabs, (d) a swipable touchscreen slider, (e) ?pressable? buttons and ?spinnable? controls of a touchscreen widget.
Affordance is not only one of the most central of HCI concepts, but also one of the most controversial: its history in HCI is abundant with twists and turns. The meaning of the concept and its relevance to HCI and interaction design have been subjects of debate for over two decades.
Gaver (1991, 1992, 1996): Affordances vs. their perception, affordances for complex actions, and multimodality
An important early analysis of affordances in the context of HCI was conducted by Gaver (1991, 1992). In his paper ?Technology affordances? (1991), which, as observed by McGrenere and Ho (2000), was the first CHI conference paper on affordances, Gaver provides an insightful, if rather succinct, discussion of a range of key issues that need to be elaborated upon in order to make affordance a useful and usable HCI concept.
First, Gaver systematically analyzes the relationship between affordances and perceptual information about affordances. He identifies four possible combinations of the presence or absence of affordances, on the one hand, and the presence or absence of information aboutaffordances, on the other hand: perceptible affordances, false affordances, hidden affordances, and correct rejection (Figure 9). As noted by McGrenere and Ho (2000), Gaver?s differentiation of affordances as such from perceptual information that specifies them (which is in line with the original Gibsonian meaning of the term) is somewhat different from Norman?s (1988) interpretation, which combines affordances and their perception.
Copyright ? William Gaver. All Rights Reserved. Reproduced with permission. See section "Exceptions" in the copyright terms below.
Figure 44.9: Separating affordances from the information available about them allows the distinction among correct rejections and perceived, hidden and false affordances. From Gaver (1991).
Second, Gaver discusses affordances for complex actions, that is, actions comprising several sub-actions. He identifies two types of such affordances:
Sequential affordances: ?acting on a perceptible affordance leads to information indicating new affordance? (Gaver, 1991, p. 82). For instance, visual information about a door handle may indicate that the handle is graspable, while grasping the handle may reveal that it is also turnable.
Nested affordances: one affordance serves as context for another one. For instance, a door handle?s affordance of graspability can be nested within the door?s affordance of pullability.
Gaver emphasizes the importance of active exploration in revealing and using affordances of complex objects. He also suggests that the role of metaphors in design should be in guiding users? exploration of a system rather than conveying the actual knowledge about how exactly the system in question is supposed to be used.
Third, Gaver points out that information about affordances is not limited to visual information. Other modalities, such as tactile information and sound, as well as their combinations, are important as well, and should be taken into account in design.
In addition, Gaver briefly comments on the issue of making affordances perceptible. He observes that the attributes of the object, which are relevant for action, should be made available for perception without using mediating representations: ?What is perceived is what is acted upon?. Designs that successfully offer perceptible affordances, according to Gaver, are employingnomically (causally) mapped graphical objects, whose meaning is directly available to the perceiver(footnote 6).
The concept of affordances has informed a number of concrete studies, conducted by Gaver, such as an investigation of how groups of people perceive and use media spaces, as opposed to regular physical spaces (Gaver, 1992; Gaver 1996).
Degree of affordance
McGrenere and Ho call for moving beyond a binary view of affordance (as something that either exists or does not exist) toward a more nuanced interpretation of the ?possibility for action?. In particular, it is argued that the difficulty of using an affordance is highly relevant to usability and should, therefore, be taken into account. McGrenere and Ho refer to the work of Warren (1995) as an example of research in ecological psychology that addresses this issue.
Functional hierarchies of affordances
Building on Gibson?s (Gibson 1979) references to nested objects in the environment and Gaver?s notion of nested affordances, McGrenere and Ho argue that affordances comprise functional hierarchies, not limited to physical interaction with the system:
?Possible actions on a computer system include physical interaction with devices such as the screen, keyboard, and mouse. But the role of affordances does not end with the physical aspect of the system [?]. The application software also provides possible actions. A word processor affords writing and editing at a high level, but it also affords clicking, scrolling, dragging and dropping. The functions that are invoke-able by the user are the affordances in software.? (McGrenere and Ho, 2000).
They also observe that:
?It is important to note that affordances exist (or are nested) in a hierarchy and that the levels of the hierarchy may or may not map to system functions.? (McGrenere and Ho, 2000).
In addition, McGrenere and Ho (2000) argue strongly for separating affordances from their perception (the position they ascribed to Gibson) because, as they claim, the separation would help researchers and practitioners to differentiate more clearly between two aspects of design, namely: designing the utility of an object (an affordance) and designing usability (the information that specifies the affordance). A similar position was also expressed by Tornvliet (2003). (This view on the issue of the relationship between affordance and perception is discussed in more detail in section 4.1 below).
Hartson (2003): Types of affordances and Norman?s model of action
Norman (1986, 1988) describes the structure of human action as an execution-evaluation cycle comprising seven stages: (1) setting a goal, (2) developing an intention to act, (3) planning a sequence of actions, (4) executing the sequence of actions, (5) perceiving the state of the world caused by the execution of the action sequence, (6) interpreting the perception, and (7) evaluating the interpretation. If the goal is achieved, the action is completed. If not, the cycle is repeated over again or the action is terminated. The model makes the task of design or evaluation more manageable by breaking it down into separate components and allowing the analyst to focus on individual stages, as well as concrete relations between the stages. The model suggests that key concerns of interaction design should be bridging the gulf of execution (stages (2) ? (4)) and the gulf of evaluation (stages (5)-(6)).
Hartson (2003) argues that Norman?s model of action can be used to make the notion of affordances more specific and applicable in the context of design. He differentiates between four kinds of affordances: cognitive, physical, sensory, and functional. These are defined as follows:
?We have named the different kinds of affordances for the role they play in supporting users during interaction, reflecting user processes and the kinds of actions users make in task performance. Norman?s perceived affordance becomes cognitive affordance, helping users with their cognitive actions. Norman?s real affordance becomes physical affordance, helping users with their physical actions. We add a third kind of affordance that also plays an important role in interaction design and evaluation, sensory affordance, helping users with their sensory actions. A fourth kind, functional affordance, ties usage to usefulness. We offer guidelines for considering these kinds of affordance together in a design context.? (Hartson, 2003, p.316, original italics).
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