Bryant's target article does an excellent job of presenting the evidence on the central portion of the functional hierarchy, but it unfortunately fails to distinguish human spatial cognition's important prerequisites and advanced forms. Some of these systems allow only "perceptual" access, others only "verbal." In this commentary I will try to support a position that does not integrate perceptual and verbal information about space into a common format.
1.2 The psychophysics of space perception is a relatively self-sufficient domain, impenetrable to "higher-level" verbal influences. Its underlying mechanisms show a dependency on both egocentric and exocentric coordinates, but always within the actual sensory field (e.g., Gibson's  optic array). Several modalities contribute to the perception of space but all this intermodal activity apparently converges on a common format (Shipley & Rowlings 1971) for which there is developmental evidence as early as the first weeks of the life (Aaronson & Rosenbloom 1972). Is this the same common format referred to in the target article? The changes in the metric of perceived space under the influence of conditions of observation and action suggest that they may not be the same; the difference is already evident when one pushes one's eye with one's finger.
1.3 Another example is provided by those implicit components of spatial experience that are "built into" our everyday spatial skills (Velichkovsky, Blinnikova & Lapin 1986). Whether we can call these "route-maps" is open to question because, for example, they can manifest themselves in an immediate tendency to "run to the left" independent of the actual direction from which one reaches a starting point. I strongly suspect that such automatisms would dissociate from one another in patients with damage to language and spatial orientation of the "survey-map" type.
1.4 The locus of the multimodal interaction described in the target article is semantic memory, where verbal information, largely topological, concerning spatial relationships (see, for example, Jackendoff & Landau 1992) is completed by default on the basis of stored spatial schemata. These interactions are more or less symmetrical: Just as the interpretation and remembering of spatiotemporal information can be modulated by verbal descriptions, so the understanding of verbal information can be influenced by nonlinguistic context. These interactions presuppose a relatively long period of development, however, and the spatial model seems to be decoupled from actual localization, motion and orientation (unless the subject is still in the early Piagetian stage when even these mechanisms depend on immediate perceptual perspective).
1.5 Still another mechanism of a quasispatial kind is involved in the structuring of mental representation according to personal intentions, interests and emotion. The best example here is Kurt Lewin's (1917) classical work on wartime landscapes. The imaginary line dividing "our" and "their" territories is quite a real thing psychologically but can it be reduced to the metric of spatial perception or to any combination of terms from the spatial lexicon? I very much doubt it. It is not accidental that those linguistic means explicitly introducing "mental spaces" into discourse (imaginary or conventional worlds as well as one's own, one's partner's or third-person perspectives on them) are different from the spatial-term segment of the lexicon (Fauconnier, 1984).
1.6 The corresponding dissociations can again be predicted. Lesley (1991) provides data on the dissociation between domains of physical causality (the tasks require sufficient spatial representational ability) and interpersonal attributions of knowledge about spatial location. The growing body of evidence on the dissociation between the semantic and the episodic/autobiographical memory systems points in the same direction too (Tulving 1992).
1.7 The picture emerging from these considerations is of several systems situated along the vertical dimension of mental functioning (Velichkovsky 1990). Bryant's target article does an excellent job of presenting the evidence on the central portion of the functional hierarchy, but it unfortunately fails to distinguish human spatial cognition's important prerequisites and advanced forms. Some of these systems allow only "perceptual" access, others only "verbal."
Aaronson, E. & Rosenbloom, S. (1972) Space perception in early infancy. Science 177: 1161-1163.
Bryant, D.J. (1992) A spatial representation system in human. PSYCOLOQUY 3 (16) space.1
Fauconnier, G. (1984) Espaces mentaux. Paris: Minuit.
Gibson, J. J. (1979) An ecological approach to visual perception. Boston: Houghton Mifflin
Jackendoff, R. & Landau, B. (1991) Spatial language and spatial cognition. In D.J.Napoli & J.A.Kegl (Eds.) Bridges between psychology and linguistics: A Swarthmore festschrift for Lila Gleitman. Hillsdale, NJ: Lawrence Erlbaum Associatates.
Leslie, A. (1991, November 1-4) Dissociations in acquiring a "Theory of mind." Paper presented to the Conference on the Mental Architecture. Centre for Cognitive Studies, Rutgers University.
Lewin, K. (1917) Kriegslandschaft. Zeitschrift fuer angewandte Psychologie 13: 440-447.
Shipley, T. & Rowlings, S.O. (1971) Sensory directions in homogenous binocular visual space. Perception & Psychophysics 9: 335-337.
Tulving, E. (1992, June 11) Human memory: Structures and processes. Paper presented to the psychophysiological seminar. Faculty of Psychology, University of Bielefeld.
Velichkovsky, B.M. (1990) The vertical dimension of mental functioning. Psychological Research 52: 282-289.
Velichkovsky, B.M., Blinnikova, J.V. & Lapin, E.A. (1986) Predstavlenije realnogo i voobrazhaemogo prostranstva [Representation of real and imaginary space]. Voprosy Psykhologii 31: 103-115.