Frontal brain potentials during recognition are modulated by requirements to retrieve perceptual detail

To assess the role of prefrontal cortex in retrieval and address the contro versy about whether prefrontal retrieval operations are engaged only follow ing successful retrieval, we recorded event-related brain potentials during two recognition tests with differing demands on retrieval effort. Both tes ts included object drawings that were (1) identical to those studied, (2) t he same but with altered aspect ratios, and (3) previously unseen. Instruct ions were to respond "old" only if drawings were not modified (specific tes t) or regardless of modifications (general test). Frontal potentials were e nhanced during the specific relative to the general test for all three type s of drawings. We conclude that these potentials reflected differential eng agement of strategic retrieval, that this function relied on left prefronta l cortex, and that it was not contingent on successful retrieval.