Laura A. Monti

Evidence for multiple mechanisms of conceptual priming on implicit memory tests

The authors examined effects of encoding manipulations on 4 conceptual-implicit memory tasks: word-cued association, category-cued association, category verification, and abstract/concrete classification. Study-phase conceptual elaboration enhanced priming for word-cued association with weakly associated words (Experiment 3), and for category-cued association with high- and low-dominance exemplars (Experiments 4 and 5), but did not enhance priming for word-cued association with strongly associated words (Experiments 1 and 2), for category verification with high- and low-dominance exemplars (Experiment 5), or for abstract/concrete classification (Experiment 7). Forms of priming that were unaffected by conceptual elaboration were not mediated by perceptual processes because they were unaffected by study-test modality changes (Experiments 6 and 8). The dissociative effects of conceptual elaboration on conceptual-implicit tasks suggest that at least 2 dissociable mechanisms mediate conceptual priming.

Intact and impaired conceptual memory processes in amnesia.

To examine the status of conceptual memory processes in amnesia, a conceptual memory task with implicit or explicit task instructions was given to amnesic and control groups. After studying a list of category exemplars, participants saw category labels and were asked to generate as many exemplars as possible (an implicit memory task) or to generate exemplars that had been in the prior study list (an explicit memory task). After incidental deep or shallow encoding of exemplars, amnesic patients showed normal implicit memory performance (priming), a normal levels-of-processing effect on priming, and impaired explicit memory performance. After intentional encoding of exemplars, amnesic patients showed impaired implicit and explicit memory performance. Results suggest that although amnesic patients can show impairments on implicit and explicit conceptual memory tasks, their deficit does not generalize to all conceptual memory tasks.

Event-related potentials of 4–7-week-old infants in a visual recognition memory task ☆

Event-related brain potentials were recorded from 4-7-week-old infants viewing a visual oddball task. During the task the duration of the infants visual fixations of the stimuli was recorded. The latency of a frontally predominant negative component (Nc) and magnitude of an early slow wave (NSW) changed as a function of stimulus experience, thereby indicating a sensitivity to the infants attention, stimulus discrimination and, perhaps, recognition memory. Nc latencies were faster and NSW magnitude was larger to the oddball stimulus than to the frequent stimulus. In addition, the latency of a component over occipital scalp. (N378) was faster to the oddball stimulus and may reflect the first perceptual registration of stimulus change. The latencies of the components allow an analysis of the infants chronometry of processing. Analysis of looking behavior indicated that the infants also gave longer oddball looks than frequent looks. The relation of the ERP data to the infants looking behavior suggests that fixation duration and the ERP components can be used as complementary measures of different aspects of the infants attentional-cognitive processes.

Preserved priming across study-test picture transformations in patients with Alzheimer's disease

Picture-naming priming was examined across different study-test transformations to explore the nature of memory representations of objects supporting implicit memory processes in patients with Alzheimers disease (AD). Although severely impaired in explicit memory for pictures and words, AD patients demonstrated normal priming across perceptual transformations in picture orientation (Experiment 1) and picture size (Experiment 2) and across symbolic transformations from words to pictures (Experiment 3). In addition, the priming across alterations in picture size was invariant. This demonstrates that AD patients have preserved implicit memory for high-level, abstract representations of objects.

Dissociation between two forms of conceptual priming in Alzheimer's disease

Patients with Alzheimers disease (AD) and healthy control participants performed 2 conceptual repetition priming tasks, word-associate production and category-exemplar production. Both tasks had identical study-phases of reading target words aloud, had the most common responses as target items, and required production of a single response. Patients with AD showed normal priming on word-associate production but impaired priming on category-exemplar production. This dissociation in AD suggests that conceptual priming is not a unitary form of memory but rather is mediated by separable memory systems.

Intact text-specific implicit memory in patients with Alzheimer's disease.

The ability of patients with Alzheimers disease (AD) to acquire and retain text-specific knowledge was investigated in a re-reading study. Patients and normal control Ss read 2 passages 3 times, each as quickly as possible, and answered recognition memory questions after the 3rd reading of each passage. The AD patients had poor explicit memory as evidenced by impaired recognition memory for the passages. In contrast, normal decreases in the times required for successive readings of each passage for AD patients indicated intact implicit memory for the passages. The absence of facilitation across passages indicated that the re-reading effect was text specific, suggesting that AD patients may retain the ability to form certain kinds of implicit new associations. Alternative accounts of the mechanism underlying text-specific priming, and of the nature of intact and impaired implicit memory in AD, are considered.

Latent Learning in Medial Temporal Amnesia: Evidence for Disrupted Representational but Preserved Attentional Processes

Damage to the hippocampus and medial temporal (MT) structures can lead to anterograde amnesia and may also impair latent learning, in which prior exposure to cues affects their subsequent associability. Normally, latent learning may reflect both representational and attentional mechanisms. Prior work has suggested that individuals with MT amnesia have specific deficits in representational processing; thus, latent learning that invokes primarily representational mechanisms might be especially impaired in MT amnesia. The current results provide preliminary confirmation of this prediction. In Experiment 1, a latent learning paradigm expected to invoke representational mechanisms was impaired in individuals with MT amnesia, whereas in Experiment 2, a paradigm expected to invoke other attentional mechanisms was spared in individuals with MT amnesia. This suggests the representational and attentional components of latent learning are dissociable and differentially affected in anterograde amnesia.

Conditional spatial discrimination in humans with hypoxic brain injury

Hypoxic brain injury can cause severe anterograde amnesia with intact intelligence and attention in select patients. This neuropsychological profile is similar among a broad class of etiologies resulting in damage to the hippocampus and associated medial temporal structures. Several recent studies have demonstrated that subjects with anterograde amnesia can nonetheless acquire simple associative tasks. In the present study, the performance of subjects with anterograde memory impairments resulting from hypoxic brain injury on a conditional spatial discrimination was examined. Quantitative magnetic resonance imaging revealed significant hippocampal atrophy in the hypoxic subjects. The hypoxic subjects were able to acquire and reverse the discrimination, although they were slower relative to matched control subjects. Hypoxic subjects also showed a tendency to perseverate after reward contingencies were reversed.

Sources of priming in text rereading: Intact implicit memory for new associations in older adults and in patients with Alzheimer's disease

The contributions of text meaning, new between-word associations, and single-word repetition to priming in text rereading in younger and older adults, and in patients with Alzheimers disease. (AD), were assessed in Experiment 1. Explicit recognition memory for text was also assessed. Equivalent single-word and between-word priming was observed for all groups, even though patients with AD showed impaired explicit memory for individual words in the text. The contribution of generalized reading task skill to priming in meaningless text rereading in younger adults was assessed in Experiment 2. Generalized reading task skill was also found to contribute to priming. These results reveal 3 mechanisms of priming: new between-word associations for meaningful and meaningless text, individual word repetition for meaningless text, and general task or skill factors for meaningless text. All priming mechanisms appear to be intact in older adults and in patients with AD.