Cognitive and neural mechanisms of decision biases in recognition memory

In recognition memory tasks, stimuli can be classified as 'old' either on the basis of accurate memory or a bias to respond 'old', yet bias has received little attention in the cognitive neuroscience literature. Here we examined the pattern and timing of bias-related effects in event-related brain potentials (ERPs) to determine whether the bias is linked more to memory retrieval or to response verification processes. Participants were divided into a High Bias and a Low Bias group according to their bias to respond 'old'. These groups did not differ in recognition accuracy or in the ERP pattern to items that actually were old versus new (Objective Old/New Effect). However, when the old/new distinction was based on each subject's perspective, i.e. when items judged 'old' were compared with those judged 'new' (Subjective Old/New Effect), significant group differences were observed over prefrontal sites with a timing (300-500 ms poststimulus) more consistent with bias acting early on memory retrieval processes than on post-retrieval response verification processes. In the standard old/new effect (Hits vs Correct Rejections), these group differences were intermediate to those for the Objective and the Subjective comparisons, indicating that such comparisons are confounded by response bias. We propose that these biases are top-down controlled processes mediated by prefrontal cortex areas.