Individuals vary greatly in their environmental-scale spatial abilities, such as their ability to point to unseen locations, and find their way through an unfamiliar neighborhood. However, causes of these individual differences are currently unclear. Therefore, in this dissertation, I have proposed that in order to understand the causes (and correlates) of individual differences in environmental-scale spatial abilities, individual differences in the processes that underlie these abilities must be fully understood. To demonstrate how this method provides insight into the individual differences in environmental-scale spatial abilities, six experiments were used to identify the correlates of individual differences in sensing directionality.

Sensing directionality is the ability to code and compare allocentric-headings, which are facing directions that are grounded in the environment, and the ability to sense directionality is essential for supporting environmental-scale spatial abilities. For example, it is difficult to point accurately towards an unseen landmark without knowing your facing direction relative to the environment, and it is your ability to sense directionality that keeps you oriented within environmental-scale spaces. To investigate the correlates of individual differences in sensing directionality, two tasks were used: the Allocentric-Heading Recall task, which involves comparing one's physical facing direction with the facing direction of a photograph (in Experiments 1-3), and the Relative Heading task, which involves comparing an imagined facing direction with a facing direction of a photograph (in Experiments 4-6).

In Experiment 1, the Allocentric-Heading Recall task was completed using a chair- turn response and accuracy rates showed an alignment effect. In Experiments 2 and 3, a strategy questionnaire was added to determine the impact of how the individual conceptualized the facing directions on task performance. Individuals who tended to use an allocentric strategy outperformed those who tended to use an egocentric strategy. In Experiments 4 and 5, the Relative Heading task was used to determine whether removing body orientation from the Allocentric-Heading task would reduce the alignment effect. In fact, removing body orientation eliminated the alignment effect, suggesting that the alignment effect found in the Allocentric-Heading Recall task was a sensorimotor alignment effect. In Experiment 6, the Relative Heading task was conducted inside an MRI scanner. This experiment found that task performance was related to caudate volume, and environmental-scale spatial abilities was related to activity patterns in the left superior parietal lobule. These experiments revealed that the ability to sense directionality depends on three factors: how the individual conceptualizes his/her environment, body orientation, and brain differences. This dissertation provides evidence that variation in sensing directionality depends on multiple factors; therefore, it is likely that variation in other processes that underlie environmental-scale spatial abilities also depend on multiple factors. In order to understand variation in environmental-scale spatial abilities, it is essential not only to identify the underlying processes that support environmental-scale spatial abilities, but to also identify the causes of variation in those underlying processes.