Of Spatial Cognition And Mental Rotation

Spatial cognition may be defined as the ability to generate, retain, retrieve, and transform well-structured visual images. Spatial ability occupies a pivotal role in all models of human ability. For example, most models of human ability state that together with verbal ability spatial cognition captures more variance than any other dimensions in large, representative batteries of ability tests (Thurstone, 1938). Spatial ability has been measured with various tests such as form boards, block manipulation, paper-folding tasks, and mental rotation tests. Many of these tasks are used in contemporary intelligence tests as measures of performance or nonverbal intelligence. A further variant of spatial tests utilizes navigation tests, in which the subjects are required to find efficient routes between locations. However, these tests show at best moderate correlations with other measures of spatial abilities. Several factor analytic studies have shown that spatial ability is not a unitary construct as reflected in the fact that performance scores of many spatial tests consistently revealed several spatial factors. On the basis of extensive reviews, Lohman (1979) identified five major factors of spatial cognition: (1) spatial visualization, (2) speeded rotation, (3) closure speed, (4) closure flexibility, and (5) perceptual speed. Linn and Petersen (1985) on the other hand identified only three factors including (1) spatial perception, (2) mental rotation, and (3) spatial visualization. Several subsequent studies have substantiated this distinction of subtypes of spatial cognition, most supporting the three-factor solution. Closure speed, closure flexibility, and perceptual speed load also on other factors not directly related to spatial cognition (e.g., executive functions or perception), thus indicating that they may not be typical for spatial cognition. According to current view, the three-factor solution is supplemented by a fourth factor representing spatial navigation. A recent development in spatial cognition has been to differentiate the investigative approach into large-scale spatial tasks where the observer is part of the environment and cannot see the entire space from one viewpoint and small-scale spatial tasks where the spatial relations of objects can be seen (Golledge and Stimson, 1997).

This research has demonstrated that mental rotation is an important aspect of spatial cognition. We will focus in the present contribution on this special subcomponent of spatial cognition because of the considerable interest it has received over the last 20 years, especially in the context of brain imaging studies. Mental rotation includes the ability to imagine how objects will appear when they are rotated. Shepard and Metzler (1971) were the first to systematically explore this function. They did so by presenting pairs of solid geometrical objects that were in form either identical or mirror images of one another and timing participants as they judged whether the pairs were the same or different. The reaction times to make same judgments increased linearly as a function of the angle between the forms, suggesting that participants mentally rotated one form into congruence with the other before making the judgment.

Although this principal result has been replicated many times it has also been noted that there are individual differences in solving the mental rotation task. The most prominent difference is a gender difference, with men normally outperforming women. Environmental (experience-dependent, spatial activities, socialization) and biological (genetic, hormonal, evolutionary) factors are often discussed as possible causes for these sex differences. It is recognized that subjects prefer different strategies, known as "analog-holistic" or "verbal-analytic strategies, in mental rotation tasks. One of the more prevailing of possible explanations for the sex differences in mental rotation is that men and women solve mental rotation tasks by using different strategies. Men are thought to use the more successful visual-spatial holistic strategies, in which they picture the object in their mind and then mentally rotate the object. Women on the other hand prefer less efficient verbal or analytic strategies with a more "piecemeal" mental rotation process. Evidence for the role of environmental factors has been found in the frequently observed relation between a person's participation in spatial activities and his or her spatial ability, as well as in the fact that performance can be improved by training (Heil et al., 1998; Newcombe et al., 1989; Quaiser-Pohl and Lehmann, 2002; Voyer et al., 1995). Environmental factors may interact with the different strategies of the two sexes. Thus, a reasonable working hypothesis is that differences in strategies underlie differences in mental rotation performances of the sexes. However, it is unclear whether the different strategies in females and males depend on sex-specific brain development or on differential socialization (Halpern, 2000; Kimura, 1999). In terms of biological factors, explanations of sex differences in spatial performance are both indirect, as evidenced by evolutionary speculations about different selective pressures on males and females when navigating in the environment (Jones et al., 2003), and direct, as demonstrated by the important role played by sex hormones in organizing a variety of sexually dimorphic behaviors. For instance, sex hormones have been shown to be important in mental rotation performance, independently of differential experience (Hausmann et al., 2000). Hausmann and colleagues have demonstrated that testosterone and estradiol are able to modulate spatial cognition during the menstrual cycle, and Maki and Resnik (Maki and Resnick, 2001) recently pointed out that sex hormones like estrogen could influence cerebral blood flow and neuronal activation in women.. Sex differences in functional cerebral organization, which may reflect organizational hormone effects, have also been implicated in differential mental rotation performance of the sexes, albeit without any direct evidence and without any suggestions as to the nature of "functional cerebral organization". There is otherwise good evidence of the influence of sex hormones present during prenatal development on human sex-typed behavior (Cohen-Bendahan et al., 2005). For example, females suffering from congenital adrenal hyperplasia (CAH) display higher spatial ability than controls. Because of an enzymatic defect caused by a single gene, individuals with CAH produce high levels of adrenal androgens at a very early stage in gestation (Cohen-Bendahan et al., 2005). Besides the above-mentioned strategic differences in solving the mental rotation problem, Kosslyn et al (Kosslyn et al., 1998; Wexler et al., 1998) propose another difference in strategies which is not directly linked to gender: an internal strategy in which one anticipates the appearance of the object prior to physically manipulating it and an external strategy in which one visualizes the consequences of someone else or an external force moving the object. The internal strategy is also sometimes called the egocentric strategy. In the following we will summarize and discuss the current literature on mental rotation where its investigation has used modern brain imaging methods. We place the emphasis on describing and discussing the brain imaging results in the context of the following topics: (1) general functional neuroanatomy of mental rotation, (2) possible hemispheric asymmetries, (3) gender differences and (4) influence of different cognitive strategies on mental rotation and the concomitant cortical activation pattern.

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