<p> Individuals often display preferences for the morning or evening; this preference is referred to as a chronotype and is supported by distinct diurnal physiological and behavioural fluctuations. Whereas prior work suggests an increase in individuals executive control throughout the day, the current study assesses the diurnal time course of executive control and the tendency to mind wander as a function of chronotype. Results suggest that executive control processes are modulated by time of day, with chronotype match conditions associated with increased executive control, akin to the 'Synchrony Effect' of chronotypes (Hasher et al., 2002). Results suggest that variations in the level of semantic processing in a task influences time of day effects on non-automatic (executive control) functioning. </p> / Thesis / Master of Science (MSc)