Collaboration in implicit memory: evidence from word-fragment completion and category exemplar generation.

Recent studies have begun to investigate the effects of collaboration on explicit tests such as free recall, cued recall, and recognition. In contrast, little is known about the impact of this variable on implicit memory. To bridge this gap, the present study compared the performance of nominal and collaborative groups in two implicit memory tasks-word-fragment completion (WFCT) and category exemplar generation (CEGT). Both the disruption-of-individual-retrieval-strategies and the retrieval blocking hypotheses predicted no significant negative effects of collaboration on repetition priming; in contrast, the retrieval inhibition hypothesis predicted lower priming in collaborative than in nominal groups in both tasks. The results supported the former hypotheses, because priming scores in the WFCT and the CEGT did not differ between collaborative and individual groups. Interestingly; however, a significant collaborative inhibition was obtained in the CEGT (but not in the WFCT) when considering the raw proportions of studied and unstudied exemplars generated. The latter finding might indicate that the performance of collaborative groups can be significantly impaired by the disruption of within-category order resulting from the exposure to the exemplars generated by other group members, even when participants do not explicitly attempt to retrieve the stimuli presented at encoding.

Divided attention enhances explicit but not implicit conceptual memory: an item-specific account of the attentional boost effect.

The Attentional Boost Effect (ABE) refers to the counterintuitive finding that words encoded with to-be-responded targets in a divided-attention condition are remembered better than words encoded with distractors. Previous studies suggested that the ABE-related enhancement of verbal memory depends upon the activation of abstract lexical representations. In the present study, we extend this hypothesis by embedding it in the context of a broader perspective, which proposes that divided attention in the ABE paradigm affects item-specific, but not relational, processing. To this purpose, we examined the ABE in the matched tasks of category-cued recall (CCRT: explicit memory) and category exemplar generation (CEGT: implicit memory). In addition, study time was varied (500, 1500 or 4000 ms), to further determine whether the attentional boost manipulation could influence late-phase elaborative processing. In agreement with the predictions of the item-specific account, the results showed that exemplars encoded with targets were recalled better than exemplars encoded with distractors in the CCRT, but not in the CEGT. Moreover, performance in the CCRT increased with study time, whereas the size of the ABE-related enhancement tended to decrease, further confirming that this effect hinges upon early phase encoding processes.

Distinct grey and white matter changes are associated with the phenomenology of visual hallucinations in Lewy Body Disease.

Visual hallucinations in Lewy body disease (LBD) can be differentiated based on phenomenology into minor phenomena (MVH) and complex hallucinations (CVH). MVH include a variety of phenomena, such as illusions, presence and passage hallucinations occurring at early stages of LBD. The neural mechanisms of visual hallucinations are largely unknown. The hodotopic model posits that the hallucination state is due to abnormal activity in specialized visual areas, that occurs in the context of wider network connectivity alterations and that phenomenology of VH, including content and temporal characteristics, may help identify brain regions underpinning these phenomena. Here we investigated both the topological and hodological neural basis of visual hallucinations integrating grey and white matter imaging analyses. We studied LBD patients with VH and age matched healthy controls (HC). VH were assessed using a North-East-Visual-Hallucinations-Interview that captures phenomenological detail. Then we applied voxel-based morphometry and tract based spatial statistics approaches to identify grey and white matter changes. First, we compared LBD patients and HC. We found a reduced grey matter volume and a widespread damage of white tracts in LBD compared to HC. Then we tested the association between CVH and MVH and grey and white matter indices. We found that CVH duration was associated with decreased grey matter volume in the fusiform gyrus suggesting that LBD neurodegeneration-related abnormal activity in this area is responsible for CVH. An unexpected finding was that MVH severity was associated with a greater integrity of white matter tracts, specifically those connecting dorsal, ventral attention networks and visual areas. Our results suggest that networks underlying MVH need to be partly intact and functional for MVH experiences to occur, while CVH occur when cortical areas are damaged. The findings support the hodotopic view and the hypothesis that MVH and CVH relate to different neural mechanisms, with wider implications for the treatment of these symptoms in a clinical context.

The Attentional Boost Effect in Young and Adult Euthymic Bipolar Patients and Healthy Controls.

In the Attentional Boost Effect (ABE), stimuli encoded with to-be-responded targets are later recognized more accurately than stimuli encoded with to-be-ignored distractors. While this effect is robust in young adults, evidence regarding healthy older adults and clinical populations is sparse. The present study investigated whether a significant ABE is present in bipolar patients (BP), who, even in the euthymic phase, suffer from attentional deficits, and whether the effect is modulated by age. Young and adult euthymic BP and healthy controls (HC) presented with a sequence of pictures paired with target or distractor squares were asked to pay attention to the pictures and press the spacebar when a target square appeared. After a 15-min interval, their memory of the pictures was tested in a recognition task. The performance in the detection task was lower in BP than in HC, in both age groups. More importantly, neither young nor adult BP exhibited a significant ABE; for HC, a robust ABE was only found in young participants. The results suggest that the increase in the attentional demands of the detection task in BP and in adult HC draws resources away from the encoding of target-associated stimuli, resulting in elimination of the ABE. Clinical implications are discussed.

Behavioral psychological symptoms of dementia and functional connectivity changes: a network-based study.

Behavioral and psychological symptoms of dementia (BPSD) are commonly observed since the early stage of Alzheimer's disease (AD) associated with structural brain changes. It is conceivable that they may also relate to functional brain changes. This resting-state functional MRI (RS-fMRI) study investigated the alterations within functional brain networks of a cohort of AD patients at different clinical stages who presented with BPSD. One hundred one AD patients and 56 patients with amnestic mild cognitive impairment underwent a neuropsychological evaluation including the Neuropsychiatry Inventory-12 (NPI-12). All patients and 35 healthy controls (HS) underwent 3T-MRI. Factor analysis was used to extract the principal factors from NPI-12, while RS-fMRI data were processed using graph theory to investigate functional connectivity. Five factors were extracted from NPI-12. Sixty-two percent of patients showed BPSD and functional brain connectivity changes in various networks compared to those without BPSD and HS. These changes contributed to account for patients' BPSD. This work opens new perspectives in terms of nonpharmacological interventions that might be designed to modulate brain connectivity and improve patients' BPSD.

When divided attention fails to enhance memory encoding: The attentional boost effect is eliminated in young-old adults.

In the Attentional Boost Effect (ABE), images or words presented with to-be-responded target squares are later recognized more accurately than images or words presented with to-be-ignored distractor squares. Surprisingly, previous studies investigating the ABE have always examined young participants: thus, the question of whether this memory facilitation can be also observed in older adults has never been tested. The present study sought to fill this gap by examining whether healthy aging modulated the size of the ABE in 4 experiments in which the nature of the background stimuli (images vs. words), the length of the encoding trials (500 vs. 1,000 ms), and the type of instructions given to participants (incidental vs. intentional) were varied. In all cases, the results showed that the ABE was robust and significant in younger adults, whereas it was completely abolished in older adults. It is suggested that the detection of target squares required more attention resources in older than in younger adults, and that these resources were subtracted from the encoding of target-associated stimuli; thus, reducing or eliminating the ABE in the older group. Alternative explanations are also discussed. (PsycINFO Database Record