Abstract
The Late Positive Complex (LPC) is an Event-Related Potential (ERP) consistently observed in recognition-memory paradigms. In the present study, we investigated whether the LPC tracks the strength of multiple types of memory signals, and whether it does so in a decision dependent manner. For this purpose, we employed judgements of cumulative lifetime exposure to object concepts, and judgements of cumulative recent exposure (i.e., frequency judgements) in a study-test paradigm. A comparison of ERP signatures in relation to degree of prior exposure across the two memory tasks and the study phase revealed that the LPC tracks both types of memory signals, but only when they are relevant to the decision at hand. Another ERP component previously implicated in recognition memory, the FN400, showed a distinct pattern of activity across conditions that differed from the LPC; it tracked only recent exposure in a decision-dependent manner. Another similar ERP component typically linked to conceptual processing in past work, the N400, was sensitive to degree of recent and lifetime exposure, but it did not track them in a decision dependent manner. Finally, source localization analyses pointed to a potential source of the LPC in left ventral lateral parietal cortex, which also showed the decision-dependent effect. The current findings highlight the role of decision making in ERP markers of prior exposure in tasks other than those typically used in studies of recognition memory, and provides an initial link between the LPC and the previously suggested role of ventral lateral parietal cortex in memory judgements.
Highlights
Recognition memory refers to the ability to recognize that a stimulus has been encountered previously
Results from a recent study called into question the classic interpretation of the Late Positive Complex (LPC) as a specific marker of episodic recollection by suggesting that the LPC tracks the perceived strength of memory even when participants cannot recollect episodic detail pertaining to the stimulus encounter[5]
To determine whether the effect observed in the FN400/N400 time window (300–500 ms) for recent exposure was tied to a condition in which this dimension is decision-relevant, we examined whether the effect was present in the study phase
Summary
Recognition memory refers to the ability to recognize that a stimulus has been encountered previously. The second ERP component is the mid-frontal FN400, characterized by an earlier peak at 400 ms, with a more positive deflection for stimuli judged to be old These two ERP components have often been interpreted in the context of the dual-process model of recognition memory, with the LPC marking recollection of episodic details about the prior stimulus encounter, and the FN400 marking item-based familiarity assessment (devoid of episodic context). Evidence that favors an interpretation of the LPC as a marker of signal strength for the memory decision at hand comes from a recent EEG-based study that fitted a drift-diffusion model to single-trial data from a recognition-memory experiment that required participants to make old/new judgements about items from a list of words[6]. Such judgements display considerable consistency across participants within a given culture[10,11,12], and engage brain structures in the medial temporal lobe that are known to play a critical role in recognition memory[7,13]
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