Measuring recollection and familiarity in the medial temporal lobe.

Many recent studies have investigated how the structures of the medial temporal lobe (MTL) support recollection and familiarity, which are two processes widely thought to support recognition memory. The behavioral methods that are used to isolate recollection and familiarity in neuroimaging and lesion studies typically assume that recollection is a categorical process and not a continuous process. A categorical process is one that either occurs or does not occur for a particular test item (yielding high confidence and high accuracy when it does occur), whereas a continuous process is one that comes in degrees (yielding varying degrees of confidence and accuracy). Studies suggesting that the hippocampus selectively supports the recollection process (such as those that use the Remember/Know procedure or rely on Receiver Operating Characteristic analysis) generally depend on the categorical view of recollection, but much recent evidence suggests that recollection is a continuous process. If recollection is a continuous process (i.e., if recollection comes in degrees), then evidence that has been taken to mean that the hippocampus selectively supports recollection is also compatible with the idea that the hippocampus supports both recollection and familiarity. We suggest that an alternative method can be used to effectively investigate recollection and familiarity in the MTL, one that is valid whether recollection is a categorical or a continuous process.