Automatic and controlled processes (ACP) are the two categories of cognitive processing. All cognitive processes are theorized to fall into one or both of those categories. The level of attention and effort (cognitive demand) required by a cognitive process is the main differentiating factor between automatic and controlled processes. Automatic processes refer to cognitive processes that occur with little or no attention, low effort/control (low cognitive demand), and can occur in parallel with other cognitive processes. Contrarily, controlled processes refer to cognitive processes that occur with attention, effortful control (high cognitive demand), and occur serially. Controlled processes are typically slower than automatic processes, and are limited by the availability of cognitive resources.