A WORKING-MEMORY MODEL OF A COMMON PROCEDURAL ERROR

Systematic errors in performance are an important aspect of human beha vior that have not received adequate explanation. One such systematic error is termed postcompletion error; a typical example is leaving one 's card in the automatic teller after withdrawing cash. This type of e rror seems to occur when people have an extra step to perform in a pro cedure after the main goal has been satisfied. The fact that people fr equently make this type of error, but do not make this error every tim e, may best be explained by considering the working memory load at the time the step is to be performed: The error is made when the load on working memory Is high, but will not be made when the load is low. A m odel of performance in the task was constructed using Just and Carpent er's (1992) CAPS that predicted that high working memory load should b e associated with postcompletion errors. Two experiments confirmed tha t such errors can be produced in a laboratory as well as a naturalisti c setting, and that the conditions under which the CAPS model makes th e error are consistent with the conditions under which the errors occu r in the laboratory.