Familiarity vs. Recollection

A common procedure for assessing the relative impairments of familiarity and recollection in amnesics is the remember/know procedure, in which subjects must indicate whether they recognize items based on familiarity (“I know that I saw it”) or on the basis of recollection (“I specifically remember seeing it”)[1]. Results from several studies with amnesics suggest that recollection is impaired to a greater degree than familiarity, which indicates to some that both that familiarity and recollection may belong to distinct memory subsystems. Further, this data is taken to show that familiarity and implicit memory may belong to distinct memory subsystems (Rugg & Yonelinas, 2003).

An alternate view of this latter conclusion comes from single process models of familiarity and recollection, in which the degree of match between studied items and a target item is calculated in the form of two overlapping probability distributions. One distribution reflects the degree of match between any target stimulus and the vectors stored in memory (the noise distribution) and a second distribution reflects the degree of match between the target item and that item’s stored vector (the signal distribution). According to this signal detection interpretation of recognition memory, familiarity judgments are made more freely than recollection judgments, which require a greater degree of match (Wixted & Stretch, 2004).

Based on a signal detection model of recollection and familiarity, one would predict consistently higher confidence ratings of “remember” than of “know” responses, regardless of whether these judgments were correct (hits) or incorrect (false alarms). This prediction has been verified by empirical data. Furthermore, one might expect that disruptions to the integrity of stored memory vectors (as in cases of hippocampal damage) would result in impaired “remember” responses before resulting in impaired “know” responses, because “remember” responses require a higher degree of match. This prediction, though not explicitly made by signal detection theorists of recognition memory, is indeed demonstrated in amnesic patients with subtotal damage to the medial temporal lobe.

With more complete damage to the system, even familiarity judgments should be impaired; indeed, just such a pattern is observed in patients with total damage to the medial temporal lobe (Wixted & Stretch, 2004). Finally, no patient has ever demonstrated preserved recollection with impaired familiarity, a result that would be expected if the two processes arise from completely distinct systems. The single-process account thus enjoys both parsimony and compatibility with empirical data.

However, recent fMRI evidence suggests that distinct anatomical regions might subserve familiarity and recollection: greater activation is elicited in left lateral parietal regions in response to “remembered” items relative to “known” items, and less MTL activity is seen in response to old items than to new items (Rugg & Yonelinas, 2003). In constrast to the explanation offered by those authors, I argue that successful “remember” judgments may involve the retrieval of spatial information from the hippocampus into parietal regions, whereas no such specific spatial information is available for “know” judgments. Parietal activity can therefore be interpreted as an effect of remembering, rather than a cause. According to this view, both “remember” and “know” judgments rely on MTL regions, whereas remember judgments rely specifically on the hippocampus.

Note: This post is part 3 of a series of posts, in which the traditional distinctions between memory systems are reviewed. The final post in this series will propose a three-system model of memory, which I argue is the minimum number of distinct systems required to explain current behavioral, neuropsychological, and neuroimaging evidence on the nature of human memory.

References:

Rugg, M. D., & Yonelinas, A. P. (2003). Human recognition memory: a cognitive neuroscience perspective. Trends in Cognitive Sciences, 7, 313-319.

Wixted, J. T., & Stretch, V. (2004). In defense of the signal detection interpretation of remember/know judgments. Psychon Bull Rev, 11, 616-641.