The harder the task, the more inconsistent the performance: a PPT analysis on task difficulty. 
Previous research has demonstrated that as task difficulty increases, task performance subsequently decreases.  These decrements in task performance as difficulty increases have been attributed to the processes individuals use to complete tasks.  Over a series of three experiments, Potential Performance Theory (PPT; Trafimow & Rice, 2008 ; 2009), was used to test the hypothesis that decreases in task performance are, in part, due to inconsistency rather than only systematic factors.  Task difficulty was manipulated in three visual search tasks by increasing set size (Experiment 1), decreasing contrast (Experiment 2), and increasing background distracters (Experiment 3).  Findings over the three studies indicated that decreases in observed task performance as task difficulty increases are primarily due to a decrease of consistency rather than systematic factors.  The theoretical implications of these findings are discussed.