In both the private and work spheres, multitasking among three or more activities has become and is continuing to evolve as a pervasive element of everyday life, and recent technological advances only seem to be exacerbating the process. Despite attempts to understand the mental processes that let humans successfully multitask, little is known about the functional cognitive level at which these mental processes take place. This thesis makes a case for the involvement of spatial ability (among other cognitive abilities) in successful multitasking behavior. It focuses on the importance of the cognitive off-loading of executive control demands onto spatial ability, due to the inherent complexity of relationships between task goals and deadlines in multitasking scenarios. Importantly, it presents a working hypothesis—the spatiotemporal hypothesis of multitasking—as a tool for making specific predictions about multitasking performance, based on individual and sex differences in spatial ability.

In Study 1, individual differences in spatial ability and executive functions emerged as independent predictors of multitasking performance. When spatial ability was decomposed into its subcomponents, only the coordinate (metric), but not categorical (nonmetric), processing of spatial relations was related to multitasking performance. Males outperformed females in both spatial ability and multitasking, and the effects were moderated by menstrual changes, in that sex differences in coordinate spatial processing and multitasking were observed between males and females in the luteal phase of the menstrual cycle, but not between males and females at menses. In Study II, multitasking performance reflected age- and sex-related differences in executive functioning and spatial ability, suggesting that executive functions contribute to multitasking performance across the adult life span, and that reliance on spatial skills for coordinating deadlines is reduced with advancing age. The results of Study III, in which the spatiotemporal hypothesis was directly scrutinized, suggest that the spatial disruption of multiple deadlines interferes with multitasking performance. Overall, these findings suggest that multitasking performance, under certain conditions, reflects independent contributions of spatial ability and executive functioning. Moreover, the results support the distinction between categorical and coordinate spatial processing, suggesting that these two basic relational processes are selectively affected by female sex hormones and are differentially effective, even across the age span, in transforming and handling temporal patterns as spatial relations in the context of multitasking. Finally, fluctuations of sex hormones exhibit a modulating effect on sex differences in spatial ability and multitasking performance.