False memories and delusional ideation in normal healthy subjects

Studies have reported substantial mnestic deficits in patients with schizophrenia. Most of this research, however, has focussed on errors of omission (poor recall/recognition) rather than commission (such as false recall/recognition). Nevertheless, recent studies report that schizophrenics show increased false recognition and speculate that this may underpin delusional ideation (Moritz et al., 2004). No previous study has examined whether such memory problems exist in normal individuals who may be prone to delusional thinking. Using the Roediger and McDermott (1995) paradigm, we investigated memory functioning in 105 normal healthy subjects divided according to performance on a measure of delusional ideation (Peters et al. Delusional Inventory: PDI Peters et al., 1999). We found significantly poorer recall in the high than low PDI group. Moreover, high PDI scorers also made more false-alarm memory recalls than low PDI scorers. In a recognition test, high and low PDI subjects did not differ in the confidence they attached to recognition of studied items, but high PDI subjects gave greater confidence for falsely accepting unseen items. This suggests that healthy subjects scoring high on a measure of delusional thinking do show an increased tendency to make false positives, but not to make false negative memory judgements.