User:Mel.Anderson20/sandbox

Affordance is a concept that was originally conceived by the psychologist James. J. Gibson to describe the opportunities for action which are provided by the environment for the individual. To name a few examples, a cup affords grasping, a bench or flat surface affords sitting or maybe climbing on, air affords breathing and water affords drinking. The Gibsonian understanding of affordance can be characterised as action possibilities latent in the environment, objectively measureable and independent of the individual’s ability to recognise them, but always in relation to the actor and therefore dependent on their capabilities. The term has been variously used in a range of fields: ecological psychology, cognitive psychology, environmental psychology, industrial design, human–computer interaction (HCI), interaction design, instructional design and artificial intelligence. Behavioural and neuroimaging studies within psychology have provided rich data to undertake the task of disseminating affordances. Temporal information regarding affordances has been provided through the use of reaction times in behavioural studies and event-related potentials in electroencephalography (EEG). Functional magnetic resonance imaging (fMRI) techniques have allowed spatial information concerning affordances to be inferred. Disorders such as ataxia and visual agnosia have enhanced understanding of neural streams in the visual cortex associated with affordances.

A theory of direct perception
Gibson’s concept of affordance emerged from his work developing a theory of perception, which Gibson referred to as an 'ecological' or 'direct' approach. Concurrent with Gibson’s theoretical development, the main branch of cognitive psychology was in the preliminary stages of establishing an information-processing approach to human cognition. Gibson rejected the conventional cognitive view of perception, which Gibson labelled 'indirect' or 'mediated.'

The indirect view of perception rests on the premise that the stimulus input available to the senses from the environment is impoverished. To account for the rich and detailed manner in which humans experience the world, it proposed that ambiguous sensory input is elaborated by mental processes to produce a detailed representation. These internal processes involve amalgamating knowledge stored in memory with the information derived from the environment. Understood as such, perception of the environment is essentially an interpretation.

Gibson’s approach was a radical departure from the traditional theories of perception; he held that humans are in direct contact with information provided by the environment. Gibson dismissed the assumptions of impoverished stimulus input and mental processes mediating perception. Instead, Gibson maintained that the environment offers such rich stimulation that perception essentially becomes the act of detecting that information.

Gibson was acutely aware of the close association between perception and action. Much of the traditional view of perception had only considered perception as a stationary act separate from action. Gibson argued, however, that in a real world situation perception occurs not merely to identify objects, but to guide action. Gibson's conception of affordances enabled him to demonstrate the proximity of this relationship between action and perception.

Conceptual features
Affordances were described by Gibson in The Ecological Approach to Visual Perception:

"The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill. The verb to afford is found in the dictionary, but the noun affordance is not. I have made it up. I mean by it something that refers to both the environment and the animal in a way that no existing term does. It implies the complementarity of the animal and the environment."

Gibson’s concept of affordance has numerous features. A caveat regarding Gibson’s work, however, is that some theorists have found his accounts confusing and oversimplified. There exists substantial difference in opinion regarding what constitutes an affordance. This could partly be attributed to Gibson’s lack of clear definition; Gibson tended to illustrate the concept through use of examples. Some of the more commonly agreed affordance properties are presented below.

One feature of affordances is that they can be understood to be relational, in that they depend upon the relation between the physical abilities of the actor and the environment. So a particular object in the environment may afford a particular action for one individual, but not for another. For example, what may afford climbing or sitting for an adult may not afford climbing or sitting for a child who is much smaller, or who may not be capable of such actions. Another feature of affordances then, is that they are also unique for each individual.

Following this, affordances can be considered real and not psychological constructs, in the ontological sense that they exist in the relation between actor and environment. Consider the argument that the relation 'taller-than' exists between a smaller object and a larger one, even though it does not inhere either object separately. Similarly, an affordance of sitting exists in the relation between an actor and a chair.

Moreover, the existence of an affordance does not depend on its perception by the actor. To illustrate this feature following Gibson’s reasoning, the affordance of ‘climbability’ may exist in the relation between an individual and a chair, independent of that individual being able to perceive the chair for the act of climbing. This affordance exists invariantly, although it may not be perceived until the individual considers climbing on the chair to change a light bulb.

Another feature of affordance, and also of significance to Gibson’s theory of perception, is the premise that affordances are meaningful. An indirect view of perception based on the assumption of impoverished sensory input entails that the environment is meaningless and thus requires mental processes to create meaning. The concept of affordance enabled Gibson to demonstrate that the environment could be rendered meaningful without making recourse to such processes, as according to this view, the environment is comprised of affordances that can be directly perceived. Meaning is proposed to be inherent in affordances, in the sense that the action possibilities offered by the environment mean that the individual can (or cannot) perform a particular action.

History
Gibson’s concept of affordance developed over his academic lifetime. Precursors to the idea of affordances can be found in early pieces of his research regarding issues of meaning, motion and perception. During World War Two, Gibson was employed by the U.S. Army Air Forces to investigate the problems and performance of pilots navigating aircraft. This research in particular drove Gibson to question the nature of the information available to the observer during such tasks of motion and perception.

The earliest specific reference to affordance appeared in Gibson’s 1966 publication The Senses Considered as Perceptual Systems. The concept of affordance was gradually conceived by Gibson during his work on this publication; at the time Gibson had been attempting to elucidate the nature of the association between behaviour and perception. Gibson introduced his theory of affordances more thoroughly as a chapter in 1977, The Theory of Affordances, which he then elaborated in his final book, The Ecological Approach to Visual Perception. It is the latter publication which has been the basis for much of the experimental work investigating affordances. Gibson’s own understanding of the concept was continuing to evolve even at this late stage, and perhaps had not reached full development when he wrote The Ecological Approach to Visual Perception in 1979. For example, several revisions and additions to definitions can be found between 1977 and 1979.

Further development
Gibson’s theories of perception and affordance have generated much controversy and debate. As mentioned previously, Gibson’s work has been critiqued as sometimes confusing and oversimplified. Despite these caveats, Gibson’s affordance concept has generated a large body of research. Contemporary researchers have advanced on Gibson’s ideas and have attempted to refine a concept which has proven difficult to encapsulate. As such, a variety of definitions can be found in the affordance literature.

Turvey, for example, presented an elaborate definition of affordance with the intention of further developing the concept and guiding research. In essence, Turvey proposed that an affordance is a property of the environment which, according to the formal logic of his argument, must be necessarily complemented by a property of the organism. Several aspects of Turvey’s definition, however, were considered incompatible with an ecological approach, in particular a definition which considered the environment as a unit separate from the organism.

Stoffregen proposed a definition in response to Tulvey. Stoffregen argued that affordances should be not be considered as a property of just the environment, but rather defined as a property of the environment and the organism in a cohesive unit. Stoffregen termed this unit the ‘animal-environment system’ and argued that this is the level at which analysis should take place.

Chemero proposed that affordances should not be defined as properties, but as relations. In alignment with Stoffregen, Chemero agreed that affordances should not be defined as a property of just the environment or the individual. Chemero's definiton, however, diverged from Stoffregen's where he argued that affordances should be defined as the relation between an aspect of the environment and the physical ability of the individual.

Donald Norman borrowed the term affordance from Gibson to discuss features of product design in his book The Psychology of Everyday Things/The Design of Everyday Things, which resulted in widespread adoption of its use in the design community. Norman's dissemination of the concept of affordance has had particular impact on the disciplines of interaction design and human-computer interaction. Norman and Gibson’s views of perception and affordance diverged on a fundamental level. Norman believed that perception and affordance occurred as the result of mental processes and interpretations, whereas Gibson rejected such premises. Gibson focused on affordance as a relationship of the actor and environment; Norman’s concern lay in the design of objects and the actions they afford. Norman focused on how the perception of an affordance can influence how an object is used, and differentiated his conception from Gibson’s by referring to it as 'perceived affordance'.

Behavioural Studies
Studies investigating affordances arguably began with a seminal study by Warren (1984) who used a body-scale paradigm for the affordance of stairs for climbing. Ratios were calculated between the dimensions of the stair (riser height and length of treads) and biomechanics of the climber, such as leg length and ratio proportion of upper to lower leg. The relation between environmental properties and climber (leg length), in terms of ratio, corresponded to the dynamics of the animal-environment system inherent in the affordance concept. However a shift away from body-scale studies to reaction time measurements in behavioural studies on affordance occurred, driven by the requirement to differentiate body scale and ability. An incongruity between ability and leg length would occur in a situation whereas an athlete could have the same leg length as an elderly lady, but their ability for stair climbing would not only be reflected by leg length. The property of the climber in the stair climbing paradigm was not a leg length ratio but a function of ability; affordance here was re-understood in terms of a relation between stepping ability of climber and features of the environment (riser height). There is a differentiation between the subjective ability, the potential for action, relative to the actor, and the objective affordance properties of the object; what the object affords is relative to the subject-object interaction.

Most behavioural studies since have utilised reaction time as a measurement for prehension, the act of grasping, which has been aligned with the actual action afforded by an object. Familiar and novel objects have become the favoured paradigm for affordance studies. Tools in particular have become a unique focal point for affordance effects, not restricted to behavioural studies but utilised in neuroimaging too. Tools offer this distinct opportunity due to the representation for action associated with tools’ visual structure for affording action (grasping) and their specific functional identity (action plans relying on previous knowledge systems).

Tipper, Paul and Hayes, (2006) in an attempt to determine processes involved in the affordance effect, ascertained that the process is not completely automatic but dependant on the object’s properties. The action properties afforded by the object distinguish whether an affordance effect occurs. It is the action-relevant features of the object which contribute to an affordance effect. Discrimination of shape was found to result in an affordance effect but colour properties did not produce an affordance effect. Information regarding shape is associated with action, grasping, whilst colour is irrelevant to action. Binary measurements used in traditional behavioural reaction tasks (the depressing of keyboard or stimulus box keys) can fail to capture subtleties in affordance tasks though. The use of a continuous force measure such as grip force is recommended which is sensitive to erroneous measurements of reaction. These measurements can reflect cognitive motor plans (the action afforded by the object) co-activated with incongruent task demands. This method provides direct evidence that motor plans, appropriate to the objects interaction, are activated by object affordances through visual processing; vision to action.

There is debate as to whether the affordance effect shown is an encoding of stimulus’ features or a shift of attention. The encoding is of the stimulus' features relevant for action of appropriate motor plans whilst the shift of attention relates to the stimulus’ orientation (location of graspable feature; a handle on the right of a pan would afford a faster response time from the right hand) which defines the response. This later attentional hypothesis proposes that the motor plans are automatically generated by an attentional modulation, a shift of directed visual attention to the spatial characteristics of the object (for instance the graspable feature provides a highly salient cue for attention). This orienting attentional process could account for aspects of the Simon effect, in which reaction times are faster when location of stimulus and response are congruent. Although attention is not excluded for the affordance effect the orienting attention found in the Simon effect is not necessary for affordance. Current thinking is that the two theories of affordance effects: motor affordance (encoding of pragmatic features of objects related to action) and spatial affordance (attention to location of graspable feature) are integrated for the visual processing of graspable objects.

Cognitive Neuroscience
Using techniques for studying affordances within the field of cognitive neuroscience, evidence has been trending away from the simplistic terminology of direct/indirect perception. fMRI and EEG have hinted at a complex interaction of cognitive pathways involved with affordances, and whilst not dismissing the Gibsonian concept of direct perception, have enabled a re-understanding of his theory. A perception-action theory that has proven to be influential in the field of affordances posited two visual systems (two-streams hypothesis) with different functional outputs: vision for perception through the ventral visual system and a vision for action through the dorsal visual system. Anatomically these neural pathways project to the inferotemporal cortex (ventral stream or ‘what’ pathway) and posterior parietal cortex (dorsal stream or ‘how’ pathway). Functional processes have been imparted for these streams such that the ventral stream perceptually processes recognition (characteristics of the object) and spatial relations whilst the dorsal system programs and controls the motor actions, the implementation of the skilled action with the object.

fMRI data using the unique characteristics of tools have supported the distinct functions of the two visual streams but have highlighted the importance of information integrated from both streams. The data have shown that planning and execution of tool-use skills happens in these separate areas but the activation of both networks with semantic tasks involving familiar tool-use strengthens the notion that affordance processes utilise both systems.

The ventral premotor cortex and supplementary motor cortex (BA 6) and posterior parietal cortex in particular the supramarginal gyrus (BA 40) in the inferior parietal lobule and BA 7 part of the superior parietal lobule are probable components for the neural dorsal stream for skilled object-related actions; whilst the posterior middle temporal gyrus and fusiform gyrus (BA 37) are implicated for the ventral stream for perception and recognition including accessing semantic information of objects.

There is a distinction made between planning, a conscious action in the ventral stream and programming, a direct unconscious action in the dorsal stream. This distinction has become apparent due to neuropsychological studies with patients with brain damage, in particular with patient D.F., who has visual agnosia with damage to her ventral stream but an intact dorsal stream. She is able to engage in specific visuo-motor actions but fails to consciously experience objects, her direct grasping action was intact but she made planning errors regarding which part of the object to grasp. She lacks the functional knowledge of the object (part of affordances). Double dissociations have been found which increase the robustness of findings regarding the functionality of the two streams. Patients with optic ataxia have damaged dorsal streams (posterior parietal cortex) such as patient IG. He is able to successfully identify objects (the inference is that this is due to his intact ventral stream) but has problems with actualising his behaviour, he cannot grasp those objects.

Evidence from event-related potentials suggest a hierarchal relationship in which the ventral system initiates action selection, planning based on information regarding object function, and directs the dorsal stream in a functional appropriate manner, the actualisation of an action response with the object. However the flexibility of the two visual systems can be detected in their interaction as an event-related potential study found that action affordance was coded faster than object recognition, a reversal of the hierarchal relationship seen above. Although the debate is still prevalent, both the dorsal stream and the ventral stream both play an important role in affordances of objects. Gibson's theory of direct perception captured the close association between action and perception. In rejecting the indirect view of perception Gibson inadvertently neglected what could be seen as a complementary rather than opposing route to perception. In contemporary thinking this distinction is encapsulated in the role of the dorsal and ventral streams, respectively, in the affordance process.