Revisiting the concept of affordances in the light of activity theoryDecember 19, 2006
From: Affordances in Activity Theory and Cognitive Systems Engineering
H. Albrechtsen, H.H.K. Andersen, S. Bodker, A.M. Pejtersen
Ris ̄ National Laboratory, Roskilde
The concept of ‘affordances’ was originally coined by American psychologist J.J. Gibson (Gibson, 1979). The concept of affordances is an important element in Gibson’s ecological theory of direct perception and action which constitutes an alternative to the information-processing paradigm. According to Gibson, action and perception are linked through real world objects that afford certain forms of action possibilities for particular species or individuals.
We as humans are able during use to discover new action possibilities.
In Gibson’s view, it is the very mutuality between actor and environment that constitutes the basis for the actor’s perception and action. Hence, the primary unit of analysis is not the actors nor the environment as distinct categories, but the total ecosystem of actors and environment. According to Gibson, affordances are material properties of the environment that can support the actor’s existence and survival.
Gibson suggests that a niche is a set of affordances that constrains possible behaviour with respect to what we are able to do in a certain niche. In addition to the tenet of mutuality between the actor and the environment, Gibson claims the necessity of available information about affordances in order for their perception and information pickup to occur.
The ontological dimension: whether affordances exist per se, independently of the actor’s perception?
The epistemological dimension: how does the actor perceive an affordance, and how does the actor decide to perform or not perform an action relative to a perceived affordance.
The primary importance lies in how we may understand the relationships between human beings and computer-based artifacts, and how we design affordances so as to improve on human computer interaction in work.
Gaver (1991) defines affordances as: properties of the world that are compatible with and relevant for people’s interaction. When affordances are perceptible, they offer a link between perception and action, hidden and false affordances lead to mistakes. Gaver proposes the following taxonomy for affordances in user interfaces:
a. Perceptible affordances: linked with perceptual information (or invariants). User interfaces can offer perceptible affordances because they can offer information about objects that can be acted upon,
b. Hidden affordances: covers existing affordances in an information system, where no perceptual information is available in the interface. They then have to be learned.
c. False affordances: covers perceptual information on a non-existing affordance, upon which users mistakenly try to act.
Gaver, as did Gibson, could be argued to follow a realist ontology in the sense that affordances are regarded as existent in the environment, independently of perception.
“Properties of the world that are compatible with and relevant for the actors’ interaction, which, when perceptible, offer a link between the actors’ perception and action” (Gaver)
• “Physical properties are stable properties that the designer adds to the interface to support human-computer interaction, based on a conceptual model of the system and actor. Symbols and constraints are not affordances, because conventions for such aspects of the world develop, whereas affordances do not” (Norman).
Analysis of a variety of everyday artefacts, such as door handles and light switches, Norman (1999): Artefacts often stand in the way of human use, rather than they mediate it. Affordances in information systems exist independently of what is visible on the screen.
The computer system already comes with built-in physical affordances (..) Most of this affordance is of little interest for the purpose of the application under design (Norman, 1999).
It implies a focus on artefacts as tools mediating or blocking mediation between user and environment, and is hence to some degree is in alignment with the activity theory conception of the relationship between user, system and work environment.
Norman’s concept is based on the notion of matching between at least two distinct models or representations involved: the user’s knowledge structures (in Norman’s terms, represented internally as “cultural constraints”, “conventions” and “logical constraints”) and the
system’s structures (in Norman’s terms, represented via a “conceptual model”). Norman confuses affordances with invariants.
Contrary to Norman, Gaver (1991) finds that culture, experience and intentions are indeed entangled in the user-system interaction. Where Norman reduces such entanglement to a mechanistic “match” between system and user representations, Gaver finds that such contexts can function to highlight certain affordances.
Gaver’s as well as Norman’s affordance concepts are rather short term, and considering
affordances as more or less static surface phenomena.
Bärentsen (2000) suggests that spatial metaphors are useful devices for representing the users’ task space and their intuitive exploration, and that the perception of affordances are dependent on the degree to which users are able to know or feel (intuition) “where they are” in ecological space. He explicitly addresses the dynamic aspect of the affordance concept, for instance through underlining the importance of what space (invariants) and time means for the learning aspect. The focus is on the understanding of the user’s exploratory context in
space and time. Bärentsen in particular mobilises the principle of situated action (Suchman, 1987) and the theory of cultural historical psychology/AT (Leontjev, 1978).
Bärentsen’s design principles involve suggestions for spatial metaphors to articulate invariants, but in addition a mapping of events (or scenes) within which the user can situate her actions and choices.
In Peirce’s terms, affordance is a sign for which the organism acts as interpretant to produce action in a given situation as the object. Thus organisms do not merely respond to stimuli, but act on the basis of meaning.” (Pickering, 1999)
Activity theory perceives the relation between human and environment as dynamic.
Activity theory and Gibsonian thinking share the basic idea that perception is not afferent, that it is connected with action. Only through acting do people perceive their environment. Activity theory insists that our action and perception are mediated by a variety of tools. Activity theory gives a useful handle for understanding the mediators, and how they are shaped.
Activity theory takes purposeful acts as the basic unit of analysis of artifacts.
The actor/user has intentions and goals, and these intentions and goals are situated.
Coupling between user, system and work task, mapped through a three level model of activity motive (‘why?’), action goal (‘how?’) and operation conditions (‘what?’), inspired by Leontjev
Activity theory insists that Gibsonian thinking is lacking a clear understanding of the relations between the social-historical dimension and the evolutionary-biological aspects of the concrete sensori-motor operations realising the actions of the individual (Bärentsen, personal communication).
Gibson (1979, 130) states that: “Man made artifacts can be seen as efforts to change and expand environment. In changing the substances and shapes of the environment humans have made more available what benefits him and less pressing what injures him.”
In the Gibsonian world, learning is about increasing differentiation. Activity theory is likely to argue that the world in which we make the differentiation changes as well, as a consequence of our actions.
This does not mean that activity theory could not be used in detecting and explaining the role affordances in learning.
Do affordances gradually expose themselves to us or do they suddenly expose themselves to us just as snap of the fingers dependent on individuals different physical and mental capabilities?
Gibson hypothesises that objects have some sort of universal function or meaning. From an activity theoretical perspective the functions or meanings of tools and other objects are actively created through interacting with the environment.
Rasmussen and Vicente (1989; 1992) worked from the assumption that in any realistic situation, a large number of inter-related affordances are available to the active organism. Their core assumption was that affordances are structured and that this structure may convey important goal-relevant information.
They mapped Gibson’s affordances towards the means-ends hierarchy. The results indicated that affordances could be structured as a means-ends hierarchy, and thereby function as a mechanism to cope with the complexity of the natural environment. The interrelationships between affordances and the levels of means-end hierarchy are articulated as “why”, “how” and “what”. The model is not truly hierarchical, but is rather a stratified model of independent layers with the “totality” of concepts or information available at each individual level. In other words, for each level, one dimension, or perspective, of the “world” is unfolded. Because the model is not truly hierarchical, the relations between the levels are not essentially nor logically given.
The means-ends model has five levels:
1. Value Properties: Purpose, Goal
2. Priorities: Abstract Function
3. Context: General Function
4. Movement: Physical Process
5. Objects and Background: Physical Form
Ecological Interface Design (EIS) principles Vicente and Rasmussen (1992):
• Support of skill-based behaviour: a gradual aggregation of singular physical movements
or cognitive processes
• Support of rule-based behaviour: supporting the actors’ cognitive control of her goal-directed behaviour through displaying perceptual and diagnostic cues for changes in the environment
• Support of knowledge-based behaviour: in particular crucial in high-risk work domains and situations requiring continual awareness and fast intervention.
As Vicente (1999) rightly mentions, EIS in particular explores the application of ecological design principles for loosely coupled work domains with a high degree of strategic task uncertainty and self-organisation, where the actors’ levels of control, learning, strategies and tasks are crucial units of analysis.
An important design rationale in the EIS approach is the notion that actors have the ability to directly perceive the state of affairs in the environment, given that the information is present in a proper format. In order to do this, the interface of a system must be transparent in the sense that the deep structure of the work is accessible to direct perception as an affordance space in a Gibsonean sense. “In Gibson’s terms, the designer must create a virtual ecology, which maps the relational invariants of the work system onto the interface in such a way that the actor can read the relevant affordances for action” (Rasmussen, Pejtersen & Goodstein, 1994, p. 129). Affordances, then, is defined is as “cues for action relevance” (Rasmussen etc. 1994).
The ecological information system supports the actor by displaying not only the overall work
domain context, but also how and where their particular prototypical tasks and decisions perform.
In EIS systems, dynamic and structured affordance spaces are developed to support the actors’ strategies and intentions in work activity. Such affordance spaces are not only developed from a means ends analysis of the work domain, but also from an analysis of actors’ strategies, tasks and intentions. That is, the affordance spaces are created from a separate analysis of the deep structure of the work domain, from its physical properties to its goals, and from a separate analysis of the actors’ recurrent behaviour, intentions and strategies (e.g. Pejtersen & Albrechtsen, 2000; Albrechtsen & Pejtersen, 2000).
In such dynamic affordance spaces, the actors’ knowledge and rule-based behavior can be supported through the display of ecological classification schemes. Ecological classification schemes articulate the semantic and socio-pragmatic infrastructures constituting the context of the actors’ exploration of knowledge in work domains. They display the invariant structures, attributes and concepts of the work or problem domain together with recurrent and dynamic relational invariant structures, attributes and concepts of the actors’ task strategies and intentions.
Networked environments that link the sites and people of loosely coupled domains, there is no object system that can function as a model for the architecture of the information system to be developed. In other words, there is no single and/or unified object system in the background that can structure the totality of context for work activity. Collections are distributed across different physical sites.
Such loosely coupled work domains are self-organised. Their infrastructure evolves within the constraints of their contributing /participating actors, including the constraints of technical possibilities, socio-historical context and development, policies etc.
Recent empirical and theoretical research on infrastructures of loosely coupled domains has identified the following levels that are entangled in each other:
1. Technical infrastructure (physical localities and the linking between these);
2. Semantic infrastructure (organization and representations of documents and information)
3. Socio-pragmatic, intentional infrastructure (knowledge and intentions of contributing/participating actors and their interrelationships, coordination and collaboration forms).
According to the activity theoretical approach, affordances of tools, as for instance computer systems, must be designed in close cooperation with the users. Firstly to detect socio-historical dimension of existing tool and the usual way of carrying out work in a collabora-
tive way. Secondly to detect which part of the work should be delegated to the computers and which part should remain in the sphere of human operations. Thirdly to design new tools with a democratic perspective in mind.
Affordances of information systems are designed on the basis of i) an analysis of the invariant functional properties of the work domain, as captured through the means-ends model; ii) an analysis of the actors’ skills-rules- knowledge; iii) an analysis of the actors’ diverse, but invariant strategies and intentions (coupling). Affordances, then, articulate and display to the actor her dynamic internal world model, and thereby also articulate dynamic mutuality of
the actor and work environment. In other words, affordances of information systems not only function to support skill-based, rule-based and knowledge-based behaviour, but also provide an additional layer of “situational meta-knowledge” to support the actors’ reflections on the outcome of actions and as well as on action possibilities.
Definition of affordances should be extended as follows: “cues for action relevance, displayed in the context of a virtual ecology of work”.
The shift between the actors’ focus on work problems and context, tools that mediate their activity and their coordination of work activities with other actors performs at several levels of action, communication and understanding. Hence, the original notion by Gibson on the actor’s dynamic shifting between foreground and background of the environment is followed.
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