Fill-in and infill errors in order memory

Many current models of memory are specified with enough detail to make predictions about patterns of errors in memory tasks. However, there are often not enough empirical data available to test these predictions. We report two experiments that examine the relative frequency of fill-in and infill errors. In immediate serial recall tasks, subjects sometimes incorrectly recall item N too soon, placing it in position N-1. The error of interest is which item is recalled after this initial mistake. A fill-in error is the tendency to recall item N-1 next, whereas an infill error is the tendency to recall item N+1 next. Both experiments reveal more fill-in than infill errors, not only overall but at each possible error location throughout the list. The overall ratio is approximately 2:1. We conclude that none of the currently existing models adequately accounts for fill-in and infill errors.