Levels of processing and amnesia affect perceptual priming in fragmented picture naming

Explaining the association between repetition priming and source memory: No evidence for a contribution of recognition or fluency

In a conjoint memory task (measuring repetition priming, recognition memory, and source memory), items recognised as previously studied and receiving correct source decisions also tend to show a greater magnitude of the repetition priming effect. These associations have been explained as arising from a single memory system or signal, rather than multiple distinct ones. In the present work, we examine whether the association between priming and source memory can alternatively be explained as being driven by recognition or fluency. We first reproduced the basic priming-source association (Experiment 1). In Experiments 2 and 3, we found that the association persisted even when the task was modified so that overt and covert recognition judgements were precluded. In Experiment 4, the association was again present even though fluency (as measured by identification response time) could not influence the source decision, although the association was notably weaker. These findings suggest that the association between priming and source memory is not attributable to a contribution of recognition or fluency; instead, the findings are consistent with a single-system account in which a common memory signal drives responding.

Amnesic patients have residual prospective memory capacities

OBJECTIVE

To investigate, in two separate studies, whether amnesic patients with a severe memory impairment can learn to perform a habitual prospective memory task when they receive immediate feedback on prospective memory failures (Study 1) and whether amnesic patients are able to benefit from previous habitual prospective memory performance after a 24-h retention interval.

METHOD

A prospective memory task was embedded in a lexical decision task (Study 1) and in a perceptual discrimination task (Study 2). Performance was compared across test halves. Participants received immediate performance feedback on prospective memory failures that served as a reminder for the prospective memory task. A retest was performed after 24 h in Study 2, but without immediate feedback in the first test half.

RESULTS

In Study 1, amnesic patients performed at a lower level than the control group, but they improved significantly across the experiment. In Study 2, the results of the first session replicated this pattern. The results of the second session showed a performance breakdown in amnesic patients. However, one single reminder was enough to boost performance again on the level of the second part of day one.

CONCLUSIONS

This indicates that amnesic patients have residual prospective memory capacities and that providing immediate feedback is a promising strategy to draw on these capacities.

Time of day affects implicit memory for unattended stimuli

We investigated whether circadian arousal affects perceptual priming as a function of whether stimuli were attended or ignored during learning. We tested 160 participants on- and off-peak with regards to their circadian arousal. In the study phase, they were presented with two superimposed pictures in different colours. They had to name the pictures of one colour while ignoring the others. In the test phase, they were presented with the same and randomly intermixed new pictures. Each picture was presented in black colour in a fragment completion task. Priming was measured as the difference in fragmentation level at which the pictures from the study phase were named compared to the new pictures. Priming was stronger for attended than ignored pictures. Time of day affected priming only for ignored pictures, with stronger priming effects off-peak than on-peak. Thus, circadian arousal seems to favour the encoding of unattended materials specifically at off-peak.

The mammillary bodies and memory: more than a hippocampal relay

Although the mammillary bodies were one of the first neural structures to be implicated in memory, it has long been assumed that their main function was to act primarily as a hippocampal relay, passing information on to the anterior thalamic nuclei and from there to the cingulate cortex. This view not only afforded the mammillary bodies no independent role in memory, it also neglected the potential significance of other, nonhippocampal, inputs to the mammillary bodies. Recent advances have transformed the picture, revealing that projections from the tegmental nuclei of Gudden, and not the hippocampal formation, are critical for sustaining mammillary body function. By uncovering a role for the mammillary bodies that is independent of its subicular inputs, this work signals the need to consider a wider network of structures that form the neural bases of episodic memory.

A single-system model predicts recognition memory and repetition priming in amnesia

We challenge the claim that there are distinct neural systems for explicit and implicit memory by demonstrating that a formal single-system 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.

Recognition memory across the lifespan: the impact of word frequency and study-test interval on estimates of familiarity and recollection

The goal of this study was to investigate recognition memory performance across the lifespan and to determine how estimates of recollection and familiarity contribute to performance. In each of three experiments, participants from five groups from 14 up to 85 years of age (children, young adults, middle-aged adults, young-old adults, and old-old adults) were presented with high- and low-frequency words in a study phase and were tested immediately afterwards and/or after a one day retention interval. The results showed that word frequency and retention interval affected recognition memory performance as well as estimates of recollection and familiarity. Across the lifespan, the trajectory of recognition memory followed an inverse u-shape function that was neither affected by word frequency nor by retention interval. The trajectory of estimates of recollection also followed an inverse u-shape function, and was especially pronounced for low-frequency words. In contrast, estimates of familiarity did not differ across the lifespan. The results indicate that age differences in recognition memory are mainly due to differences in processes related to recollection while the contribution of familiarity-based processes seems to be age-invariant.

Stress effects on working memory, explicit memory, and implicit memory for neutral and emotional stimuli in healthy men

Stress is a strong modulator of memory function. However, memory is not a unitary process and stress seems to exert different effects depending on the memory type under study. Here, we explored the impact of social stress on different aspects of human memory, including tests for explicit memory and working memory (for neutral materials), as well as implicit memory (perceptual priming, contextual priming and classical conditioning for emotional stimuli). A total of 35 young adult male students were randomly assigned to either the stress or the control group, with stress being induced by the Trier Social Stress Test (TSST). Salivary cortisol levels were assessed repeatedly throughout the experiment to validate stress effects. The results support previous evidence indicating complex effects of stress on different types of memory: A pronounced working memory deficit was associated with exposure to stress. No performance differences between groups of stressed and unstressed subjects were observed in verbal explicit memory (but note that learning and recall took place within 1 h and immediately following stress) or in implicit memory for neutral stimuli. Stress enhanced classical conditioning for negative but not positive stimuli. In addition, stress improved spatial explicit memory. These results reinforce the view that acute stress can be highly disruptive for working memory processing. They provide new evidence for the facilitating effects of stress on implicit memory for negative emotional materials. Our findings are discussed with respect to their potential relevance for psychiatric disorders, such as post traumatic stress disorder.