A Single-System Model Predicts Recognition Memory and Repetition Priming in Amnesia

Abstract

We challenge the claim that there are distinct neural systems for explicit and implicit memory by demonstrating that a formal singlesystem model predicts the pattern of recognition memory (explicit) and repetition priming (implicit) in amnesia. In the current investigation, human participants with amnesia categorized pictures of objects at study and then, at test, identified fragmented versions of studied (old) and nonstudied (new) objects (providing a measure of priming), and made a recognition memory judgment (old vs new) for each object. Numerous results in the amnesic patients were predicted in advance by the single-system model, as follows: (1) deficits in recognition memory and priming were evident relative to a control group; (2) items judged as old were identified at greater levels of fragmentation than items judged new, regardless of whether the items were actually old or new; and (3) the magnitude of the priming effect (the identification advantage for old vs new items) overall was greater than that of items judged new. Model evidence measures also favored the single-system model over two formal multiple-systems models. The findings support the single-system model, which explains the pattern of recognition and priming in amnesia primarily as a reduction in the strength of a single dimension of memory strength, rather than a selective explicit memory system deficit.

A critical role of the human hippocampus in an electrophysiological measure of implicit memory

“…The current findings extend that assumption, since it provides evidence for a critical role of the human hippocampus in implicit memory processing for single items, and indicates that hippocampal patients are relying upon dramatically distinct neural systems for implicit memory processing than control subjects are. The current EEG data hence provides critical new insight into implicit memory processing in amnesia, and it qualifies the possibility that differences in implicit memory processing may actually be a common (though previously unidentified) component of amnesia that existing behavioral methods may have been insensitive to detecting (Berry et al, 2006; Berry et al, 2014; Berry et al, 2008a, b; Berry et al, 2012; Blaxton, 1992; Jernigan et al, 2001; Ostergaard, 1999). …”

“…One possible account of the data is that results may be consistent with single-systems models of memory, which propose that there are similar underlying components to both implicit and explicit memory systems (Berry et al, 2014; Berry et al, 2008b) that could each be reliant upon the same neural structures (such as the hippocampus, for example). However, the reliable topographic dissociations that were found between the physiology associated with implicit memory effects (Figure 1) and the explicit memory effects (FN400) occurring during the same time window (Figure 4) weighs considerably against this view.…”

“…the hippocampus), but also preserves the view that they operate as distinct functional systems (e.g. : Hamann and Squire, 1997), and as such remain problematic for single system accounts (Berry et al, 2014; Berry et al, 2008a, b). …”

Alzheimer’s disease and memory strength: Gradual decline of memory traces as a function of their strength

“…For instance, memory performance of amnesic patients may be reproduced in healthy young and/or elderly adults by increasing the delay of testing (Van der Linden & Bruyer, 1991) or by degrading the perceptual information available (HE, aMCI and AD patients, Cronin-Golomb, Gilmore, Neargarder, Morrison, & Laudate, 2007). These effects were interpreted by the authors based on previous findings that amnesic patients have weaker memory traces than controls (see also Berry, Kessels, Wester, & Shanks, 2014). Alternatively, weaker memory traces may decline at a similar rate than stronger traces.…”

Perceptual identification task points to continuity between implicit memory and recall

“…Specifically we focused on recall of context as our index of recollection (i.e., memory source; Slotnick, 2010). In short, we aimed to extend previous results suggesting that one continuous memory signal drives recognition and priming (e.g., Berry et al, 2012;Berry Kessels, Wester, Shanks, 2014;Berry, Ward, Shanks, 2017) to a task for which familiarity processes are theoretically less relevant. In a first experiment, we used a procedure where we evaluated repetition priming, recognition, and recall of a particular context from encoding.…”