The Concept of Affordance and GIS: A Note on Llobera (1996)
Webster, David S., Antiquity
Marcos Llobera (1996: 612) attempts to use Geographical Information Systems (GIS) in a more `humanistic way', to explore `places and spaces' and to `close the gap between theory and method'. The theory in question is that of human practices and relates to Gidens' concept of structuration and Bourdieu's concept of habitus. As a methodological tool, GIS offers, as Kvamme (1993: 91) notes, `excellent display capabilities together with embedded systems of quantitative analysis [that] can provide an ideal environment for spatial investigation'.
Gidens and Bourdieu are now regular sources for archaeological theorizing, but the American psychologist, James J. Gibson is not. Gibson studied perception and developed an `ecological psychology' based on a theory of direct perception. The concept of affordance is central to the theory of direct perception.
For Llobera, the concepts of structuration, habitus and affordance make up a trinity of key concepts that, it is hoped, will make human practices within the landscape explicable (but note; the utility of the concept of practices for social science has been severely questioned by Stephen Turner (1994)).
Finally, Llobera's approach to understanding `places and spaces' in the Wessex landscape is also influenced by the anthropology of Tim Ingold, who in turn, draws on Gibson's theory of direct perception. Llobera is therefore doubly influence by Gibson; directly by his attempt to use the concept of affordance and indirectly through the anthropology of Ingold. What, then, does Gibson's theory of direct perception amount to?
Gibson's theory of `direct perception'
Although Gibson's theory of direct perception is generally applicable to the senses, most of the experimental work he undertook explored the processes of visual perception, so I will confine my discussion to vision.
Orthodoxy (Descartes onwards) holds that light falls onto the retina producing a `retinal image' from which the mind/brain constructs representations of things in the world. Visual cognition thus amounts to manipulating these representations.
Gibson, however, contested the relevance of the `retinal image' for vision. Gibson pointed out that light entering the environment -- as rays of radiation -- is reflected back and forth off surfaces and is scattered by particulate matter in the atmosphere. In this way radiant light becomes illumination and an ambient array at every point. Thus, light comes to every point and thereby environs every point. In this way, light at the point of observation is different in intensity in different directions.
As we move through this ambient array, invariant ratios of illumination intensity presented in temporal sequence constitute a structure or texture in the form of deeply nested sets of invariant relations of illumination; these nested sets of invariant ratios of illumination are what are registered or picked up by the perceptual system. By perceptual system, Gibson means the reflexive organization of the animal -- the mobile eye on a mobile head on a mobile body. Perception for Gibson is active and exploratory. Gibson rejected the idea that the world is reassembled from a projected image on the retina, rather, the world is specified in a lawful and reflexive way by our direct interaction with it.(1)
Affordances of the environment
The lawful specification of the environment's layout given by invariant relations of illumination in ambient light carries a qualitative value for a given animal. It is this qualitative value that Gibson termed an affordance.
Gibson (1986: 127) states that The affordances of the environment are what it offers the animal, what it provides or furnishes either for good or ill. The invariants in the optical flow consist of `lower-order' and `higher-order' invariants. These two classes of invariants are interrelated, analogously, with the way ratio or interval scales (e.g. numbers) are related to nominal or ordinal scales (e.g. categories). The lower-order invariants specify the facts of environmental lay-out and thus specify the joint relations between the surfaces of the environment including those of oneself and others. The higher-order invariants are compounded from lower-order invariants and specify the affordance properties of the environment for the animal. Put otherwise, higher-order invariants specify to an animal which of its action systems might realize an affordance offered by its environment.
The following example adapted from Reed et al. (1986) should help here. A hotel lift contains an adult and two children, one aged nine, the other aged four. The lift starts perfectly level with the ground floor, but at each subsequent level the lift stops above the floor, such that with each new level reached the gap between the lift and the floor gets bigger. If the adult and the children were to get out of the lift at the first level up, there would be no problem stepping out. But if they get out on second level, the four-year-old has to have her hand held while stepping out, lest she over-balance. However, the nine-year-old and the adult can still step out without losing their balance. Now, if they get out on the third level, the adult can still step out but has to take care not to over-balance, the nine-year-old has to jump and the four-year-old has to be lifted out by the adult.
The lower-order invariances specify the joint relations between the surfaces of the lift, the building it is giving access to, and the bodies of the people concerned. The higher-order invariances arise out of the combined lower-order invariance of the environment. On the ground and first level, all three are afforded stepping out of the lift. By the third level only the adult can step out. The height between the floor and the lift can vary continuously (lower-order invariance) but the affordance of stepping out is bounded to different ranges of height above the floor (higher-order invariances) depending on the height -- thus leg length -- of the individual in question. It may be said that the lift sometimes affords stepping out, but sometimes not, depending on who wishes to step out. For the nine-year-old, the affordance of stepping out become the affordance of jumping off.
In the case of social affordance there are two or more loci of action, but only one with nonsocial affordance. For instance, when a person approaches a narrow opening, the opening does not respond (get narrower or expand) to the fact that the person is turning sideways on in order to pass through it. With social affordance, however, each individual can see that they are being experienced in some way and, in consequence, each will guide at least some of their conduct in accordance with the perceived identity and on-going responses of the other. The metaphor of a dance comes to mind here.
The problem with explicating or unfolding the structure of action being afforded is that actions can be described in either narrow or broad terms and in many intermediate ways. The trajectory of action can be carved up in a multitude of ways depending on what seems appropriate for the analysis being undertaken. Still & Good (1992) faced this problem with their study of the social affordances present when feeding an infant. In the transcripts of a recorded feeding session, they tried to give as complete a description as possible at the level of meaningful action. But it became clear that even the simplest actions can have a rich and unique meaning within the flow of activity. This meaning gets lost if they are treated as invariant and repeatable units of action for the purposes of description. In other words, the necessity of third-person description results in a necessary loss of information. In lived experience we do not act in accordance with a priori descriptive analysis, we do our experiential analysis `on-line' under conditions of constant feedback and adjustments. As Still & Good (1992: 117) remark, `there is no single action "eating with a spoon" because different instances are embedded within different contexts'.
The affordances of Wessex ditches
Llobera (1996: 622) wishes to use `GIS to explore affordances in the landscape derived from an individual's perspective within it.' But it should be clear (it is hoped) from the foregoing discussion that the presentations of affordances to an individual are intimately dependent on the specifics of the individual, e.g. their height, physical strength, manipulative skills and modes of interaction with others (and the relations of social power operating). And although `affordance' is a noun, there is no thing that is an affordance that can be seen, felt or heard, rather, affordance is the apprehension of possible actions with what we see, hear and feel.
Places and spaces, as Ingold rightly contends, are marked by the quality of our `dwelling' within them. Ingold (1993:156) states that `the landscape is the world as it is known to those who dwell therein, who inhabit its places and journey along its paths connecting them'. But knowing here is a `knowing how' not a `knowing that' that is, knowing as skilled performance. Our dwelling within a place is marked by what the individual can bring to the animal side of the affordances offered by its immediate environment. Perception presents to us the possible transformations of the places within which we dwell. But again, the concept of affordance is internal to an account of the processes of perception, and while we may gloss matters with locutions such as `a pencil affords grasping' we must be prepared to specify in detail the who and the when (and whatever else) to make good on our analytical accounts.
It may be the case that GIS can be used in constructing the rather detailed and dynamic description required to tease out one flow of affordance as opposed to some other. Certainly, Llobera (or whoever) needs to go beyond the mere adopting of a standard height for their viewing individual (i.e. 1.6 m), but I suppose that is, at least, a start.
(1) Current theories of vision are somewhat more `Gibsonian' than when Gibson was alive, in that the importance of invariance is accepted. Nevertheless, the central role of representations maintains its grip, but that too is beginning to slip.
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DAVID S. WEBSTER, Department of Psychology, University of Durham, Science Laboratories, South Road, Durham DH1 3LE, England. email@example.com & firstname.lastname@example.org…
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Publication information: Article title: The Concept of Affordance and GIS: A Note on Llobera (1996). Contributors: Webster, David S. - Author. Journal title: Antiquity. Volume: 73. Issue: 282 Publication date: December 1999. Page number: 915. © 2008 Antiquity Publications, Ltd. COPYRIGHT 1999 Gale Group.
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