The direct equation of vision with perception appears to be implicit in almost all of the more theoretically-led applications of GIS to the study of the archaeological record (for example Wheatley 1995). In some cases it is explicit:
The analysis of this data involved the calculation of the viewshed for each monument, that is the area which can be seen from an individual site... it is perhaps better to emphasise the ability of such a procedure to provide a mapable, spatially variable index of perception.. (Gaffney et al 1995b, 54)
It can be argued, however, that a notion of perception based solely upon what can, and cannot, be seen is a gross and inadequate simplification. Instead, a broad definition will be offered here which serves to define perception not in solely visual terms, but instead as both the multi-sensual reception of information about the world and the sense made of that information, mediated by factors such as memory, experience, education and expectation (Rodaway 1994). Integral to this is the notion of the importance of the physical environment to human perception. In his discussions relating to the development of a more sensuous geography, Rodaway, like Ingold before him, makes extensive reference to Gibson's theory of ecological perception (Ingold 1986). The key point here is that the structure and texture of the environment is a necessary determinant of what is perceived:
Potential sources of stimulation pass through the environment and are encoded with the structure of that environment as they are modified in their passage. It is this structured information that the sense organs 'read'. Therefore, the environment becomes a source of information, not merely raw data. (Rodaway 1994, 20)
This is contra to more Cartesian, cognitivist views of perception which characterise 'the natural world' as a reality external to humanity and a source of nothing more than raw sense data without order or meaning. What is known of the environment results from the mental processing of poor-quality sense data. Ingold characterises this cognitivist view of perception as a mode of construction of the world and not a mode of engagement with it, and sees it as serving only to reinforce an artificial culture-nature dualism. To Gibson, perception is more than the mental sorting and processing of sense data; instead the human brain, sense organs and environmental context are seen as an integrated system.
Whilst explicitly acknowledging the multi-sensual nature of perception, Gibson's work, rather like Tilley's phenomenological approach to archaeological landscape studies (Tilley 1994), has been principally articulated in visual terms (Gibson 1979; for a detailed summary see: Rodaway 1994, 19-22; Ingold 1992, 45-46). Rodaways contribution has been to elaborate Gibson's ideas in the context of a more fully sensuous geographic approach to people and place:
sight paints a picture of life, but sound, touch, taste and smell are actually life itself. A sensuous geography may therefore lay some claim to reasserting a return of geographical study to...everyday life as a multisensual and multidimensional situatedness in space and in relation to places (Rodaway 1994, 4)
In his discussion as to the multi-sensual nature of perception, Rodaway moves beyond the structure of the human body as a basic orienting system to identify four broad sensual categories. He takes pains to stress however, that these categories are largely artificial as senses rarely if ever work in isolation. They can be defined as visual (sight), auditory (sound), olfactory (smell) and haptic (touch). Reliance upon vision at the expense of the other senses, or perhaps more importantly believing that there is a reliance upon the visual, can be termed 'visualism' and it must also be acknowledged that this notion of vision as the dominant mode of perception is situated both culturally and historically within our present, western civilisation. What has to be emphasised is that even when vision is identified as somehow dominant it never functions independently of the other senses, nor is it in any way objective (Bender 1993, Thomas 1993). In relating vision directly with perception then, viewshed-based analyses must be seen as a fundamentally flawed first step towards a more reflexive GIS rather than a clear solution to current theoretical limitations, and practitioners must once again be wary of simplification for the sake of technical convenience. Even when a single sensory mode is deemed primary, for example sound to the forest-dwelling Umeda of New Guinea (Gell 1995) or vision to the white middle-class academic of western Europe, it never functions in isolation. A more fully multi-sensual notion of perception, stressing the synergy of culture-nature relations provides a much fuller template upon which to proceed.
A further limitation with the 'viewshed as panacea' approach relates to the precise mechanisms employed in not only undertaking these vision-based analyses but in interpreting the findings. The results of archaeological GIS-based visibility analyses and viewshed calculations are presented to the consuming archaeologist in a very abstracted way. The researcher is treated as detached and external, situated in a privileged location far removed from the features under study. The results are also by their very nature highly prescriptive; this area can be seen, this area cannot. In abstracting and presenting the results of the various analyses in this way the researchers may well be producing the mapable spatial indexes they desire, but they are negating the essentially experiential nature of the perceptive act they are purporting to represent, and are denying the opportunity for the archaeologist-researcher to negotiate, articulate and participate to some degree with the natural-cultural landscape under study. The practical implementation of these more experiential notions is currently being explored in the context of a re-appraisal of research undertaken in the Tisza flood-plain of North-east Hungary (see Section 1.4.1), though it should be noted that this work is very much in its infancy.
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Last updated: Tue Sep 5 1996