Influence of response bias and internal/external source on lateral posterior parietal successful retrieval activity.

In studies of recognition memory, regions of the lateral posterior parietal cortex exhibit greater activity (as indexed by the fMRI BOLD signal) during correct recognition of "old" (studied) items than correct rejection of "new" (unstudied) items. This effect appears to be source-sensitive, with greater activity associated with recognition of perceived than imagined events. Parietal successful retrieval activity also varies with response bias, or the tendency to be conservative about making "old" judgments. Here, we examined whether differences in response bias associated with recognition judgments of perceived and imagined events could account for source-based differences in LPPC activity. Participants perceived and imagined items in response to cue words and then at test, made recognition judgments in blocks that knowingly contained either a high or low proportion of old to new trials. While participants were indeed more conservative when making judgments about perceived than imagined events, the neuroimaging results demonstrated that response bias and source effects occurred in non-overlapping parietal regions. These findings suggest that source-based differences in LPPC activity cannot be explained by differences in response bias associated with recognizing perceived and imagined events.