A double dissociation between linguistic and perceptual representations ofspatial relationships

This paper explores from a neuropsychological perspective the relation betw een the meanings of English locative prepositions (e.g., in, on, above, bel ow) and the kinds of representations that are used for many visuospatial pr ocesses such as recognising, drawing, and constructing spatially complex ob jects. One possibility that has been proposed by some psycholinguists is th at 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 semanti c structures that are distinct from the representations that underlie many visuospatial abilities. Here we report a detailed assessment of the linguistic as well as perceptua l and cognitive representations of spatial relationships in two brain-damag ed subjects. Four tests were administered that involve both the production and comprehension of English locative prepositions. In addition, four stand ardised neuropsychological tests that probe high-level nonlinguistic visuos patial perception and cognition were administered. Case I was significantly impaired on all of the preposition tests but was normal on all of the visu ospatial tests. In striking contrast, Case 2 was normal on all of the prepo sition tests but was significantly impaired on all of the visuospatial test s. The subjects also had entirely different brain lesions: Case 1 had a lef t-hemisphere lesion in the frontoparietal region, and Case 2 had a right-he misphere lesion in the frontoparietal and temporal regions. Together, the r esults constitute a "double dissociation, suggesting that the preposition t ests and the visuospatial tests require cognitively and neurally distinct m echanisms that can be disrupted independently of each other. We interpret t he data as supporting the second possibility described - namely, that the m eanings of locative prepositions may be language-specific semantic structur es that are separate from the mental representations underlying many other kinds of high-level nonlinguistic visuospatial abilities.