Coordinating multiple tasks requires a high degree of cognitive control, and individuals with limited executive functions often show difficulties in everyday multitasking. We tested the hypothesis that demands on executive control can be alleviated by internally representing the temporal pattern of goals and deadlines as spatial relations. In two experiments, participants completed a multitasking session by monitoring deadlines of four clocks running at different rates, along with separate tasks of executive functioning and spatial ability. In Experiment 1, individual and gender-related differences in spatial ability (mental rotation) predicted multitasking performance, beyond the contributions of both the updating and inhibition components of executive functioning, and even when spatial cues were eliminated from the layout of the monitoring task. Experiment 2 extended these findings by showing that concurrent spatial load impaired task monitoring accuracy, and that these detrimental effects were accentuated when spatial abilities were compromized due to fluctuation in female sex hormones. These findings suggest that multiple task monitoring involves working memory-related functions, but that these cognitive control demands can be offloaded by relying on spatial relation processes.

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.

Many everyday activities require coordination and monitoring of complex relations of future goals and deadlines. Cognitive offloading may provide an efficient strategy for reducing control demands by representing future goals and deadlines as a pattern of spatial relations. We tested the hypothesis that multiple-task monitoring involves time-to-space transformational processes, and that these spatial effects are selective with greater demands on coordinate (metric) than categorical (nonmetric) spatial relation processing. Participants completed a multitasking session in which they monitored four series of deadlines, running on different time scales, while making concurrent coordinate or categorical spatial judgments. We expected and found that multitasking taxes concurrent coordinate, but not categorical, spatial processing. Furthermore, males showed a better multitasking performance than females. These findings provide novel experimental evidence for the hypothesis that efficient multitasking involves metric relational processing.

Many everyday activities require coordination and monitoring of multiple deadlines. One way to handle these temporal demands might be to represent future goals and deadlines as a pattern of spatial relations. We examined the hypothesis that spatial ability, in addition to executive functioning, contributes to individual differences in multitasking. Participants completed a multitasking session in which they monitored four digital clocks running at different rates. We predicted and found that individual differences in spatial ability and executive functions were independent predictors of multiple-task performance. Individual differences in spatial ability were also selectively related to multiple-task performance, as only coordinate spatial processing, but not categorical, predicted multitasking, even beyond executive functioning and numeracy. Furthermore, males outperformed females in spatial ability and multitasking and these sex differences generalized to a complex simulation of everyday multitasking. Menstrual changes moderated these effects 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. Overall, these findings suggest that multiple task performance reflects independent contributions of spatial ability and executive functioning. Furthermore, our results support the distinction of categorical vs. coordinate spatial processing, and suggest that these two basic relational processes are selectively affected by female sex hormones and differentially effective in transforming and handling temporal patterns as spatial relations in the context of multitasking.

We tested the spatiotemporal hypothesis of multitasking, which posits that under high temporal load, individuals with better spatial abilities are better at multitasking. A computerized multitasking simulation was administered under three different conditions, one ordinary and two conditions with additional concurrent spatial load. Participants were assigned to one of three groups, luteal females, menstrual females and males. Based on the literature, these groups differ in spatial abilities because of hormonal fluctuations linked to the menstrual cycle. Across all three versions of the multitasking simulation, the performance of the luteal group was lowest, while the menstrual and the male group did not differ significantly from each other. The results support the notion that participants with better spatial ability are better multitaskers.

We often need to monitor and coordinate multiple deadlines. One way to handle these temporal demands might be to represent future deadlines as a pattern of spatial relations. More specifically, we tested the hypothesis that multitasking reflects selective effects of coordinate (i.e., metric) relational processing. Participants completed two multitasking sessions under concurrent processing demands of coordinate versus categorical spatial information. We expected and observed that multitasking impairs concurrent coordinate, rather than categorical, spatial processing. In Experiment 1, coordinate-task performance was selectively decreased, while multitasking performance was equal under both load conditions. When emphasizing equal (primary/secondary) task-importance in Experiment 2, it was only multitasking performance that was selectively reduced under the coordinate-load condition. Thus, effective multitasking may partly reflect coordinate-relational processing.

Many everyday activities require coordination and monitoring of multiple deadlines. One way to handle these temporal demands might be to represent future goals and deadlines as a pattern of spatial relations. We examined the hypothesis that spatial ability, in addition to executive functioning, contributes to individual differences in multitasking. In two studies, participants completed a multitasking session in which they monitored four digital clocks running at different rates. In Study 1, we found that individual differences in spatial ability and executive functions were independent predictors of multiple-task performance. In Study 2, we found that individual differences in specific spatial abilities were selectively related to multiple-task performance, as only coordinate spatial processing, but not categorical, predicted multitasking, even beyond executive functioning and numeracy. In both studies, males outperformed females in spatial ability and multitasking and in Study 2 these sex differences generalized to a simulation of everyday multitasking. Menstrual changes moderated the effects on multitasking, 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. Overall, these findings suggest that multiple-task performance reflects independent contributions of spatial ability and executive functioning. Furthermore, our results support the distinction of categorical versus coordinate spatial processing, and suggest that these two basic relational processes are selectively affected by female sex hormones and differentially effective in transforming and handling temporal patterns as spatial relations in the context of multitasking.

Coordinating multiple tasks with narrow deadlines is particularly challenging for older adults because of age related decline in cognitive control functions. We tested the hypothesis that multiple task performance reflects age- and gender-related differences in executive functioning and spatial ability. Young and older adults completed a multitasking session with four monitoring tasks as well as separate tasks measuring executive functioning and spatial ability. For both age groups, men exceeded women in multitasking, measured as monitoring accuracy. Individual differences in executive functioning and spatial ability were independent predictors of young adults' monitoring accuracy, but only spatial ability was related to sex differences. For older adults, age and executive functioning, but not spatial ability, predicted multitasking performance. These results suggest that executive functions contribute to multiple task performance across the adult life span and that reliance on spatial skills for coordinating deadlines is modulated by age.

Combining study and test trials during learning is more beneficial for long-term retention than repeated study without testing (i.e., the testing effect). Less is known about the relative efficacy of different response formats during testing. We tested the hypothesis that overt testing (typing responses on a keyboard) during a practice phase benefits later memory more than covert testing (only pressing a button to indicate successful retrieval). In Experiment 1, three groups learned 40 word pairs either by repeatedly studying them, by studying and overtly testing them, or by studying and covertly testing them. In Experiment 2, only the two testing conditions were manipulated in a within-subjects design. In both experiments, participants received cued recall tests after a short (similar to 19 min) and a long (1 week) retention interval. In Experiment 1, all groups performed equally well at the short retention interval. The overt testing group reliably outperformed the repeated study group after 1 week, whereas the covert testing group performed insignificantly different from both these groups. Hence, the testing effect was demonstrated for overt, but failed to show for covert testing. In Experiment 2, overtly tested items were better and more quickly retrieved than those covertly tested. Further, this does not seem to be due to any differences in retrieval effort during learning. To conclude, overt testing was more beneficial for later retention than covert testing, but the effect size was small. Possible explanations are discussed.

This study assessed risk behavior and preventive measures for hepatitis C among injecting drug users in Rotterdam, the Netherlands (452 participants, 2002-2003) and Stockholm, Sweden (310 participants, 2004-2006), two cities with contrasting drug policies. Uni- and multivariate logistic regression models were used. We found that the prevalence of hepatitis C was almost two times higher in participants from Stockholm than in participants from Rotterdam, even after adjustment for sex sharing paraphernalia (adjusted relative risk: 1.92, 95% confidence interval: 1.60-2.29). Follow-up comparative studies are needed to determine if policies with structured health programs can decrease transmission of hepatitis C.