Abstract : The report describes the second study in a program of research dealing with the relationships between the characteristics of human tasks and the abilities required for task performance. The goal of the program is to generate principles which can be used to identify ability requirements from knowledge of the characteristics of a task and of variations in the conditions of task performance. The present study investigated the relationship between variations in an electronic fault-finding task and consequent changes in the abilities related to fault-finding performance. Characteristics of the fault-finding task were manipulated by varying formal difficulty and perceptual complexity. Subjects received a battery of reference ability tests and then proceeded to perform the criterion task under the different experimental conditions. To determine the relationship between task characteristics and ability requirements, the reference battery was factor analyzed to identify a reference ability structure. The loadings of the various criterion task conditions on that structure were then estimated. (Modified author abstract)