A double dissociation between linguistic and perceptual representations of spatial relationships.

This paper explores from a neuropsychological perspective the relation between the meanings of English locative prepositions (e.g., in, on, above, below) and the kinds of representations that are used for many visuospatial processes such as recognising, drawing, and constructing spatially complex objects. One possibility that has been proposed by some psycholinguists is that the meanings of prepositions are the same as the representations used in these other processes. An alternative possibility, which has been proposed by a different group of researchers, is that the relation is more distant such that the meanings of prepositions constitute language-specific semantic structures that are distinct from the representations that underlie many visuospatial abilities. Here we report a detailed assessment of the linguistic as well as perceptual and cognitive representations of spatial relationships in two brain-damaged subjects. Four tests were administered that involve both the production and comprehension of English locative prepositions. In addition, four standardised neuropsychological tests that probe high-level nonlinguistic visuospatial perception and cognition were administered. Case 1 was significantly impaired on all of the preposition tests but was normal on all of the visuospatial tests. In striking contrast, Case 2 was normal on all of the preposition tests but was significantly impaired on all of the visuospatial tests. The subjects also had entirely different brain lesions: Case 1 had a left-hemisphere lesion in the frontoparietal region, and Case 2 had a right-hemisphere lesion in the frontoparietal and temporal regions. Together, the results constitute a "double dissociation," suggesting that the preposition tests and the visuospatial tests require cognitively and neurally distinct mechanisms that can be disrupted independently of each other. We interpret the data as supporting the second possibility described-namely, that the meanings of locative prepositions may be language-specific semantic structures that are separate from the mental representations underlying many other kinds of high-level nonlinguistic visuospatial abilities.