Academic journal article Memory & Cognition

Lateralization of Spatial Categories: A Comparison of Verbal and Visuospatial Categorical Relations

Academic journal article Memory & Cognition

Lateralization of Spatial Categories: A Comparison of Verbal and Visuospatial Categorical Relations

Article excerpt

Many reports show that spatial relations between and within objects show differences in hemispheric lateralization. Coordinate, metric relations concerning distances are processed with a right-hemisphere advantage, whereas a left-hemisphere advantage is thought to be related to categorical, abstract relations (Kosslyn, 1987). Kemmerer and Tranel (2000) argued that the left-hemisphere advantage for categorical processing might apply only for verbal spatial categories, however, whereas a right-hemisphere advantage is related to visuospatial categories. To test this idea, we examined categorical processing for stimuli in both verbal and visuospatial formats, with a visual half-field, match-to-sample design. In Experiment 1, we manipulated the format of the second stimulus to compare response patterns for both verbal and visuospatial stimuli. In Experiment 2, we varied the expectancy of the format of the second stimulus, allowing for an assessment of strategy use. The results showed that a left-hemisphere advantage was related to verbal stimulus format only, but not in all conditions. A right-hemisphere advantage was found only with a visuospatial expectancy, visuospatial format, and brief interval. The theory we present to explain these results proposes that the lateralization related to basic categorical processing can be strongly influenced by verbal characteristics and, to some extent, by additional coordinate processing. The lateralization measured in such cases does not represent lateralization related purely to categorical processing, but to these additional effects as well. This stresses the importance of careful task and stimulus design when examining categorical processing in order to reduce the influence of those additional processes.

Spatial relation processing is a vital element in the perception of our surroundings. It provides us with information about where things are and how we can interact with them spatially. These relations have often been described as belonging to two general classes: categorical, relative, abstract labels like "left of," and coordinate, metric descriptions like "one meter apart" (Kosslyn, 1987). Along with these definitions, Kosslyn and colleagues (Kosslyn, 1987; Kosslyn et al., 1989) proposed a difference between the two types of spatial relations with regard to hemispheric lateralization; categorical relations show a left-hemisphere advantage, whereas coordinate relation processing depends more on a right-hemisphere circuitry (see, e.g., Hellige & Michimata, 1989; Laeng & Peters, 1995; Rybash & Hoyer, 1992; see also Jager & Postma, 2003). Notably, the right-hemisphere advantage for coordinate processing has been supported by numerous reports, whereas the lefthemisphere advantage for categorical processing has been smaller or absent in some studies (see Laeng, Chabris, & Kosslyn, 2003). So far, factors such as individual differences like gender (Rybash & Hoyer, 1992) and variation in difficulty (see, e.g., Martin, Houssemand, Schiltz, Burnod, & Alexandre, 2008) have been regarded as potential causes for these inconsistencies. The effects of both of these factors are still a matter of debate, however, and they do not seem clearly linked to the inconsistencies of categorical processing in particular.

Kemmerer and Tranel (2000) provided a theory of how task demands might determine the direction of lateralization. They suggested that spatial categories can be divided into two different classes. Their results indicated that only the use of linguistic categories is impaired by lefthemisphere damage, whereas a right-hemisphere lesion disturbed the processing of solely perceptual, or visuospatial categories. Using an elaborate battery of tests, they illustrated this double dissociation by contrasting one left-hemisphere patient with one right-hemisphere patient. Their linguistic tests focused on the use of spatial prepositions, whereas the perceptual tests- conventional neuropsychological tests-are considered to not have any verbal characteristics. …

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