Affordance
Encyclopedia
An affordance is a quality of an object, or an environment, which allows an individual to perform an action. For example, a knob affords twisting, and perhaps pushing, while a cord affords pulling. The term is used in a variety of fields: perceptual psychology
, cognitive psychology
, environmental psychology
, industrial design
, human–computer interaction
(HCI), interaction design
, instructional design
and artificial intelligence
.
As explained below, different definitions of affordance have developed. The original definition described all action possibilities that are physically possible. This was then refined to describe action possibilities of which an actor is aware. The term has further evolved for use in the context of HCI as indicating the easy discoverability of possible actions.
Affordances were further studied by James Gibson's wife, Eleanor J. Gibson
, who created her theory of perceptual learning around this concept. Eleanor Gibson's book, "An Ecological Approach to Perceptual Learning and Development" explores affordances further.
Jakob von Uexküll had already discussed the concept in the early twentieth century, calling it the "functional colouring" (funktionale Tönung) of objects.
appropriated the term affordances in the context of human–machine interaction
to refer to just those action possibilities that are readily perceivable by an actor. Through his book The Design of Everyday Things
, this interpretation was popularized within the fields of HCI and interaction design
. It makes the concept dependent not only on the physical capabilities of an actor, but also the actor's goals, plans, values, beliefs, and past experiences. If an actor steps into a room with an armchair and a softball
, Gibson's original definition of affordances allows that the actor may throw the recliner and sit on the softball, because that is objectively possible. Norman's definition of (perceived) affordances captures the likelihood that the actor will sit on the recliner and throw the softball. Effectively, Norman's affordances "suggest" how an object may be interacted with. For example, the size and shape of a softball obviously fits nicely in the average human hand, and its density and texture make it perfect for throwing. The user may also bring past experiences to bear with similar objects (baseballs, perhaps) when evaluating a new affordance.
Norman's 1988 definition makes the concept of affordance relational rather than subjective or intrinsic. This he deemed an "ecological approach," which is related to systems-theoretic
approaches in the natural and social sciences. The focus on perceived affordances is much more pertinent to practical design
problems from a human-factors
approach, which may explain its widespread adoption.
Norman later explained that this restriction in meaning of the term had been unintended, and that he would replace the term by "perceived affordance" in any future revision of the book. However, the definition from his book has become established enough in HCI that both uses have to be accepted as convention in this field.
This has then in turn given rise to a use of the verb afford – from which Gibson's original term was derived – in a way that is not consistent with its dictionary definition. Rather than "to provide" or "to make available", designers and those in the field of HCI often use afford as meaning "to suggest" or "to invite".
The different meanings now associated with the word, although closely related, can be a source of confusion in writing and conversation if the intended meaning is not made explicit and if it is not used consistently. Even authoritative textbooks can be inconsistent in their use of the term.
. In his article, Gaver explains that a hidden affordance indicates that there are possibilities for action, but these are not perceived by the actor. At a perceptible affordance, there is perceptible information available for an existing affordance, meaning that the actor perceives and then acts upon the existing affordance. This means that when affordances are perceptible they offer a direct link between perception and action, and when affordances are hidden or false, they lead to mistakes and misunderstandings.
Perceptual psychology
Perceptual psychology is a subfield of cognitive psychology that is concerned specifically with the pre-conscious innate aspects of the human cognitive system: perception....
, cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....
, environmental psychology
Environmental psychology
Environmental psychology is an interdisciplinary field focused on the interplay between humans and their surroundings. The field defines the term environment broadly, encompassing natural environments, social settings, built environments, learning environments, and informational environments...
, industrial design
Industrial design
Industrial design is the use of a combination of applied art and applied science to improve the aesthetics, ergonomics, and usability of a product, but it may also be used to improve the product's marketability and production...
, human–computer interaction
Human–computer interaction
Human–computer Interaction is the study, planning, and design of the interaction between people and computers. It is often regarded as the intersection of computer science, behavioral sciences, design and several other fields of study...
(HCI), interaction design
Interaction design
In design, human–computer interaction, and software development, interaction design, often abbreviated IxD, is "the practice of designing interactive digital products, environments, systems, and services." Like many other design fields interaction design also has an interest in form but its main...
, instructional design
Instructional design
Instructional Design is the practice of creating "instructional experiences which make the acquisition of knowledge and skill more efficient, effective, and appealing." The process consists broadly of determining the current state and needs of the learner, defining the end goal of instruction, and...
and artificial intelligence
Artificial intelligence
Artificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...
.
As explained below, different definitions of affordance have developed. The original definition described all action possibilities that are physically possible. This was then refined to describe action possibilities of which an actor is aware. The term has further evolved for use in the context of HCI as indicating the easy discoverability of possible actions.
Affordances as action possibilities
Psychologist James J. Gibson originally introduced the term in his 1977 article "The Theory of Affordances" and explored it more fully in his book The Ecological Approach to Visual Perception in 1979. He defined affordances as all "action possibilities" latent in the environment, objectively measurable and independent of the individual's ability to recognize them, but always in relation to the actor and therefore dependent on their capabilities. For instance, a set of steps which rises four feet high does not afford the act of climbing if the actor is a crawling infant. Gibson's is the prevalent definition in cognitive psychology.Affordances were further studied by James Gibson's wife, Eleanor J. Gibson
Eleanor J. Gibson
Eleanor J. Gibson was an American psychologist. Among her contributions to psychology, the most important are the study of perception in infants and toddlers...
, who created her theory of perceptual learning around this concept. Eleanor Gibson's book, "An Ecological Approach to Perceptual Learning and Development" explores affordances further.
Jakob von Uexküll had already discussed the concept in the early twentieth century, calling it the "functional colouring" (funktionale Tönung) of objects.
Affordances as perceived action possibilities
In 1988, Donald NormanDonald Norman
Donald Arthur Norman is an academic in the field of cognitive science, design and usability engineering and a co-founder and consultant with the Nielsen Norman Group. He is the author of the book The Design of Everyday Things....
appropriated the term affordances in the context of human–machine interaction
Human-machine interaction
Human–machine Interaction is the interaction between machines and the persons who operate them. An old-fashioned term is is Man-machined Interaction - Related terms:...
to refer to just those action possibilities that are readily perceivable by an actor. Through his book The Design of Everyday Things
The Design of Everyday Things
The Design of Everyday Things is a best-selling book by cognitive scientist and usability engineer Donald Norman about the design of simple objects, and why some objects please their users while others frustrate them....
, this interpretation was popularized within the fields of HCI and interaction design
Interaction design
In design, human–computer interaction, and software development, interaction design, often abbreviated IxD, is "the practice of designing interactive digital products, environments, systems, and services." Like many other design fields interaction design also has an interest in form but its main...
. It makes the concept dependent not only on the physical capabilities of an actor, but also the actor's goals, plans, values, beliefs, and past experiences. If an actor steps into a room with an armchair and a softball
Softball
Softball is a bat-and-ball sport played between two teams of 10 to 14 players. It is a direct descendant of baseball although there are some key differences: softballs are larger than baseballs, and the pitches are thrown underhand rather than overhand...
, Gibson's original definition of affordances allows that the actor may throw the recliner and sit on the softball, because that is objectively possible. Norman's definition of (perceived) affordances captures the likelihood that the actor will sit on the recliner and throw the softball. Effectively, Norman's affordances "suggest" how an object may be interacted with. For example, the size and shape of a softball obviously fits nicely in the average human hand, and its density and texture make it perfect for throwing. The user may also bring past experiences to bear with similar objects (baseballs, perhaps) when evaluating a new affordance.
Norman's 1988 definition makes the concept of affordance relational rather than subjective or intrinsic. This he deemed an "ecological approach," which is related to systems-theoretic
Systems theory
Systems theory is the transdisciplinary study of systems in general, with the goal of elucidating principles that can be applied to all types of systems at all nesting levels in all fields of research...
approaches in the natural and social sciences. The focus on perceived affordances is much more pertinent to practical design
Design
Design as a noun informally refers to a plan or convention for the construction of an object or a system while “to design” refers to making this plan...
problems from a human-factors
Human factors
Human factors science or human factors technologies is a multidisciplinary field incorporating contributions from psychology, engineering, industrial design, statistics, operations research and anthropometry...
approach, which may explain its widespread adoption.
Norman later explained that this restriction in meaning of the term had been unintended, and that he would replace the term by "perceived affordance" in any future revision of the book. However, the definition from his book has become established enough in HCI that both uses have to be accepted as convention in this field.
Further shift of meaning
Norman's adaptation of the concept has seen a further shift of meaning, in which the term affordance is used as an uncountable noun, referring to the property of an object or system's action possibilities being easily discoverable, as in "this web page has good affordance," or "this button needs more affordance."This has then in turn given rise to a use of the verb afford – from which Gibson's original term was derived – in a way that is not consistent with its dictionary definition. Rather than "to provide" or "to make available", designers and those in the field of HCI often use afford as meaning "to suggest" or "to invite".
The different meanings now associated with the word, although closely related, can be a source of confusion in writing and conversation if the intended meaning is not made explicit and if it is not used consistently. Even authoritative textbooks can be inconsistent in their use of the term.
False affordance
William Gaver divided affordances into three categories: perceptible, hidden, and false. A false affordance is an apparent affordance that does not have any real function, meaning that the actor perceive nonexistent possibilities for action. A good example of a false affordance is a placebo buttonPlacebo button
A placebo button, also called an idiot button, is a push-button with apparent functionality that actually has no effect when pressed, analogous to a placebo. In other cases, a control like a thermostat may not be connected....
. In his article, Gaver explains that a hidden affordance indicates that there are possibilities for action, but these are not perceived by the actor. At a perceptible affordance, there is perceptible information available for an existing affordance, meaning that the actor perceives and then acts upon the existing affordance. This means that when affordances are perceptible they offer a direct link between perception and action, and when affordances are hidden or false, they lead to mistakes and misunderstandings.