Enhancing the quantity and accuracy of eyewitness memory via initial memory testing

Previous studies have demonstrated the benefits of initial memory testing in terms of "inoculating" eyewitness memory against forgetting. The aim of the present study was to determine to what extent and under which conditions such testing may also enhance the accuracy of subsequent retrieval. Two aspects of interpolated testing were manipulated: the mode of interpolated testing (forced verbatim vs. free level) and its timing (immediate vs. delayed). After witnessing a target event, participants were questioned about event details either immediately or after a 48-h delay, and were either required to respond at the verbatim level or were given control over the grain size of their responses. Verbatim memory for event details was finally tested 72. h after the event under both standard forced-report conditions and free-report conditions. Immediate interpolated testing was found to improve both memory quantity and memory accuracy on the final test, whereas delayed interpolated testing improved only memory quantity (and to a lesser extent). Although the mode of interpolated testing affected performance on the initial test, it had no effect on either memory quantity or memory accuracy on the final test. Practical implications with regard to eyewitness questioning are discussed.