Cognitive disturbances can occur in the early stages of the disease and sometimes prior to diagnosis, and increase in prevalence with duration of the disease.[1][42] The most common cognitive deficit in PD is executive dysfunction, which can include problems with planning, cognitive flexibility, abstract thinking, rule acquisition, inhibiting inappropriate actions, initiating appropriate actions, working memory, and control of attention.[42][43] Other cognitive difficulties include slowed cognitive processing speed, impaired recall and impaired perception and estimation of time.[42][43] Nevertheless, improvement appears when recall is aided by cues.[42] Visuospatial difficulties are also part of the disease, seen for example when the individual is asked to perform tests of facial recognition and perception of the orientation of drawn lines.[42][43]