The effects of unitization on the contribution of familiarity and recollection processes to associative recognition memory: evidence from event-related potentials

Changes in the level of unitization moderate the impact of unitization on associative memory and its underlying processing

The viewpoint that unitization provides a possibility of increasing the contribution of familiarity to associative memory has been widely accepted, but its effects on associative memory and recollection remain controversial. The current study aims to explain these mixed results by considering a potential moderator: changes in the level of unitization from encoding to retrieval phases. During the encoding phase, participants learned the related and unrelated picture pairs (i.e., high vs. low levels of unitization). Subsequently, they needed to distinguish between the intact and rearranged pairs during retrieval, where, in these rearranged pairs, the level of unitization from encoding to retrieval phases may or may not change. Meanwhile, the scalp electroencephalographic activity (EEG) was recorded. The results showed a significant familiarity-related FN400 old/new effect for related picture pairs alone, which supported the above viewpoint. However, its impact on the associative memory and recollection-related LPC old/new effects varied with the level of unitization changes-specifically, under the unchanged conditions. Although related pairs elicited significant FN400 and LPC old/new effects, the differences in these old/new effects and associative memory between the related and unrelated picture pairs were not significant. Conversely, under the changed conditions, related picture pairs not only elicited significantly larger FN400 and LPC old/new effects but also improved associative memory more than unrelated picture pairs. These findings not only clarify some of the inconsistencies in the literature concerning the impact of unitization on associative memory but also suggest that unitization affects the contributions of familiarity and recollection to associative memory differently, its effectiveness varying with the level of unitization changes.

Improving associative memory in younger and older adults with unitization: evidence from meta-analysis and behavioral studies

Introduction

The finding that familiarity can support associative memory by unitizing the to -be-learned items into a novel representation has been widely accepted, but its effects on overall performance of associative memory and recollection are still controversial.

Methods

The current study aims to elucidate these discrepancies by identifying potential moderating factors through a combined approach of meta-analysis and behavioral experiment.

Results

Results consistently showed that changes in the level of unitization and age groups were two important moderators. Specifically, unitization enhanced younger and older adults' associative memory and its supporting processes (i.e., familiarity and recollection) when the level of unitization between studied and rearranged pairs was changed. However, when this level remained constant, unitization exhibited no impact on associative memory and familiarity in younger adults, but showed an enhanced effect in older adults. Furthermore, results revealed a marked group difference between younger and older adults in associative memory when the unitization level of noncompound words remained unaltered. Upon breaking this condition, the group difference was reduced by enhancing familiarity or recollection.

Discussion

These findings not only clarify some of the inconsistencies in the literature concerning the impact of unitization on associative memory, but also suggest that unitization is a beneficial strategy for reducing group difference in associative memory, with its effectiveness varying according to the level of unitization changes.

The effect of part-list cuing on associative recognition

The modulation of part-list cuing on item memory has been well-documented, whereas its impact on associative memory remains largely unknown. The present study explored the effect of part-list cuing on associative recognition and, more specifically, whether this forgetting effect caused by part-list cuing is more sensitive to recollection or familiarity in recognition memory. Experiments 1a and 1b combined the intact/rearranged/new judgement task of associative recognition with the classical part-list cuing paradigm, and the result showed that part-list cuing impaired the recognition accuracy of "intact" and "rearranged" face-scene pairs. Moreover, the discriminability score of relational recognition and item recognition was significantly decreased in the part-list cuing condition compared to the no-part-list cuing condition. Experiments 2a and 2b further used the Remember/Know/Guess task to explore which recognition processes (recollection vs. familiarity) were sensitive to the presentation of part-list cuing. The results showed that part-list cuing reduced the familiarity of relational recognition and the recollection and familiarity of item recognition. These findings suggest that part-list cuing was harmful to the recognition of relationships (familiarity) and items (recollection and familiarity) in associative memory.

Lesion-behavior mapping indicates a strategic role for parietal substrates of associative memory

Numerous neuroimaging studies indicate that ventral parietal cortex (VPC), especially angular gyrus, plays an important role in episodic memory. However, the nature of the mnemonic processes supported by this region is far from clear. We previously found that stroke lesions in VPC and lateral temporal cortex caused deficits in cued recall of unimodal word pairs and picture pairs, and cross-modal picture-sound pairs, with larger deficits in the cross-modal task. However, those findings leave open the question whether those regions' integrity is necessary for maintenance of associative representations, or for strategic processes required for their recall. We addressed this question using associative recognition versions of those tasks. We additionally manipulated semantic relatedness of the associated memoranda, to assess VPC's involvement in semantic processing in the context of episodic memory. We analyzed performance of 62 first-event, sub-acute phase stroke patients (31 right- and 31 left-hemisphere damage) relative to 65 healthy participants, and employed voxel-based lesion-behavior mapping (VLBM) to identify task-relevant structures. Patients displayed greater false associative recognition of semantically related compared to unrelated recombined pairs. VLBM analysis implicated right lateral temporo-parietal regions in associative recognition deficits in the cross-modal pairs task, specifically for related recombined and new pairs, seemingly because of difficulty overcoming semantic relatedness bias effects on episodic discrimination. In contrast, damage to ventral parietal and lateral temporal cortex was not implicated in memory for unrelated memoranda. We interpret this pattern of lesion-behavior effects as indicating lateral temporo-parietal cortex involvement in strategic, rather than representational, roles in episodic associative memory.

From encoding to retrieval: Change in level of unitization resolves debate about Unitization's effect on associative recognition

Although it is widely accepted that familiarity could support associative recognition when the to-be-learn items are 'unitized' into a new representation, the effects of unitization on associative recognition and recollection remain much debated. The current study aimed to explain these debates by exploring when and how unitization benefits associative recognition using event-related potentials (ERPs). During the encoding phase, participants learned compound words and unrelated word pairs (i.e., High vs. Low level of unitization). At retrieval, the compound words were rearranged into new compound words (i.e., no-change) and unrelated word pairs (i.e., change). Similarly, the unrelated word pairs were rearranged into new unrelated word pairs (i.e., no-change) and compound words (i.e., change). Results showed that under the no-change condition, unitization did not affect associative recognition, nor its underlying processes. In contrast, under the change condition, unitization improved associative recognition by increasing both familiarity-related FN400 effect and recollection-related LPC effect. In addition, a planned comparison between the compound-change and unrelated-no change conditions-a common index for unitization effect in past studies-revealed that unitization could not only elicit significant FN400 effect, but also improve associative recognition by increasing LPC effect. Collectively, these results not only allowed to explain the current discrepancies in the literature concerning the effect of unitization on associative recognition, but also emphasized the importance of matching the level of unitization between the studied and rearranged word pairs.

Inflammation, depression, and anxiety related to recognition memory in young adults

Previous research suggests that common modifiable health risk factors (e.g., depression, anxiety, metabolic illness, inflammation) may have an impact on memory. In the present study, we sought to investigate relationships between a number of these health risk factors and two components of recognition memory (recollection and familiarity). Data were analyzed for 96 healthy young adults between 17 and 25 years old. Recollection and familiarity were measured using an associative recognition procedure involving unitized and unrelated word pairs, and regression analyses were used to relate recognition memory performance to physical health (inflammation via plasma IL-6 levels, central obesity via waste-to-hip ratio, and heart rate variability) and mental health (depression via CESD-R, stress via PSS, and state and personality trait anxiety via STAI) measures of modifiable risk factors. Together, these health variables predicted an additional 19% of the variance in recollection beyond what was accounted for by familiarity, and 15% of the variance in familiarity beyond what was accounted for by recollection. These effects were primarily driven by inflammation, depression, and trait anxiety, which were each significant (p < .05) independent predictors of recognition. Higher levels of depression and inflammation were related to worse recollection yet better familiarity. Higher levels of trait anxiety were related to better recollection but were not related to familiarity. These findings demonstrate complex relationships between these modifiable health risk factors and recognition memory. Future longitudinal and cross-sectional research is needed to further explore these relationships and determine whether or not poor health causes these changes in recognition.

Effects of emotion and semantic relatedness on recognition memory: Behavioral and electrophysiological evidence

Some aspects of our memory are enhanced by emotion, whereas others can be unaffected or even hindered. Previous studies reported impaired associative memory of emotional content, an effect termed associative "emotional interference". The current study used EEG and an associative recognition paradigm to investigate the cognitive and neural mechanisms associated with this effect. In two experiments, participants studied negative and neutral stimulus-pairs that were either semantically related or unrelated. In Experiment 1 emotions were relevant to the encoding task (valence judgment) whereas in Experiment 2 emotions were irrelevant (familiarity judgment). In a subsequent associative recognition test, EEG was recorded while participants discriminated between intact, rearranged, and new pairs. An associative emotional interference effect was observed in both experiments, but was attenuated for semantically related pairs in Experiment 1, where valence was relevant to the task. Moreover, a modulation of an early associative memory ERP component (300-550 ms) occurred for negative pairs when valence was task-relevant (Experiment 1), but for semantically related pairs when valence was irrelevant (Experiment 2). A later ERP component (550-800 ms) showed a more general pattern, and was observed in all experimental conditions. These results suggest that both valence and semantic relations can act as an organizing principle that promotes associative binding. Their ability to contribute to successful retrieval depends on specific task demands.

Recollection and familiarity in schizophrenia:An ERP investigation using face recognition exclusion tasks

Recent studies suggest that the recollection deficit observed in schizophrenia may not be a unitary phenomenon but could depend on the information to retrieve. Here we investigated whether the nature of the perceptual information affects recollection and familiarity in schizophrenia. ERP old/new effects were explored in 20 patients with schizophrenia and 20 healthy controls during unfamiliar face exclusion tasks, with either intrinsic (expression) or extrinsic (background) information either changing or remaining the same between study and test. Schizophrenia patients rejected old faces as distractors in a greater extent than healthy controls. The FN400 old/new effect (300-500ms) was found in both groups. It was sensitive to facial expression change for healthy controls but not schizophrenia patients. In addition, the parietal old/new effect was lower for correctly excluded faces for patients, but not for controls. This points to the conclusion that schizophrenia patients discriminate between target and non-target faces on the basis of the memory strength signal corresponding to the study-test mismatch rather than the recollection of the critical information, as observed in healthy controls. This functioning can be useful when study-test perceptual mismatch must be detected but, in return, can lead to the over-exclusion of old stimuli.

The different effects of concept definition and interactive imagery encoding on associative recognition for word and picture stimuli

Traditional view holds that associative recognition require recollection while familiarity can't support associative recognition. However, recent research indicate that familiarity can also contribute to associative recognition when the stimuli are unitized in encoding. Here, we investigated the electrophysiological correlates of retrieval of word and picture stimuli in three encoding conditions. Semantically unrelated word pairs or picture pairs were encoded in concept definition, interactive imagery, and item comparison conditions, separately. In test, the participants were required to discriminate between old pairs that appeared in the same pairing as in study, rearranged pairs that appeared in different pairings in study, or completely new pairs. The behavioral results revealed that higher associative recognition was observed in interactive imagery condition than in concept definition condition, with item comparison condition eliciting the worst recognition, regardless of word or picture stimuli. ERP results of word stimuli revealed that the FN400 old/new effect was solely elicited in concept definition and interactive imagery conditions, but not in item comparison condition. However, ERP results of picture stimuli revealed that the late FN400 old/new effect was observed in three encoding conditions and that larger magnitude of old/new effect was elicited in item comparison condition than in interactive imagery condition. There may be different neural mechanisms of unitization on associative recognition for word and picture stimuli. These findings suggested that the pattern of engagement of familiarity during successful retrieval was dependent on the stimulating properties and the encoding conditions. We will discuss the possibility that top-down unitization which manipulates two unrelated stimuli through instructions may lead to the engagement of specific forms of familiarity-association familiarity and item familiarity.

Unitization of internal and external features contributes to associative recognition for faces: Evidence from modulations of the FN400

Associative recognition requires discriminating between old items and conjunction lures constructed by recombining elements from two different study items. This task can be solved not only by recollection but also by familiarity if the to-be-remembered stimuli are perceived as a unitized representation. In two event-related potential (ERP) studies, we provide evidence for the integration of internal and external facial features by showing that the early frontal old-new effect (considered a correlate of familiarity) is modulated by the specific combination of facial features. Participants studied faces consisting of internal features (eyes, eyebrows, nose, and mouth) paired with external features (hair, head shape, and ears). During the testing phase, intact, recombined, and new faces were presented. Recombined faces consisted of internal and external features taken from two different studied faces. The results showed that at the frontal sites, during the time window from 300 to 500 ms, ERPs to intact faces were more positive than those to new and recombined faces; the latter two did not differ from one another. The late parietal effect was observed only after a more extended study phase in Experiment 2. We take the modulation of the early frontal old-new effect as evidence for the contribution of familiarity to associative recognition for combinations of internal and external facial features.

Repetitive Transcranial Magnetic Stimulation Improved Source Memory and Modulated Recollection-Based Retrieval in Healthy Older Adults

Source memory is one of the cognitive abilities that are most vulnerable to aging. Luckily, the brain plasticity could be modulated to counteract the decline. The repetitive transcranial magnetic stimulation (rTMS), a relatively non-invasive neuro-modulatory technique, could directly modulate neural excitability in the targeted cortical areas. Here, we are interested in whether the application of rTMS could enhance the source memory performance in healthy older adults. In addition, event-related potentials (ERPs) were employed to explore the specific retrieval process that rTMS could affect. Subjects were randomly assigned to either the rTMS group or the sham group. The rTMS group received 10 sessions (20 min per session) of 10 Hz rTMS applying on the right dorsolateral prefrontal cortex (i.e., F4 site), and the sham group received 10 sessions of sham stimulation. Both groups performed source memory tests before and after the intervention while the electroencephalogram (EEG) was recorded during the retrieval process. Behavioral results showed that the source memory performance was significantly improved after rTMS compared with the sham stimulation; ERPs results showed that during the retrieval phase, the left parietal old/new effect, which reflected the process of recollection common to both young and old adults, increased in the rTMS group compared with the sham stimulation group, whereas the late reversed old/new effect specific to the source retrieval of older adults showed similar attenuation after intervention in both groups. The present results suggested that rTMS could be an effective intervention to improve source memory performance in healthy older adults and that it selectively facilitated the youth-like recollection process during retrieval. This study was registered in the Chinese Clinical Trial Registry (ChiCTR) with the identifier chictr-ire-15006371.

Under the condition of unitization at encoding rather than unitization at retrieval, familiarity could support associative recognition and the relationship between unitization and recollection was moderated by unitization-congruence

It is widely accepted that associative recognition can be supported by familiarity through integrating more than two stimuli into a unit, but there are still three unsolved questions: (1) how unitization affects recollection-based associative recognition; (2) whether it is necessary to match the level of unitization (LOU) between original and rearranged pairs, which was term as unitization-congruence (UC); (3) whether unitization can occur at encoding or at retrieval. The purposes of this study are to try to answer these questions. During the encoding phase, the participants were asked to learn compound words and unrelated word pairs, and during the retrieval phase, they needed to distinguish intact pairs from rearranged consistent and rearranged inconsistent pairs with "remember/know" paradigm. The results showed that (1) the role of unitization in recollection was moderated by UC; (2) Under the consistent UC condition, unitization could improve familiarity-based associative recognition without affecting recollection-based associative recognition, while under the inconsistent UC condition, unitization could improve familiarity-based and recollection-based associative recognition simultaneously, these results indicated that it was necessary to match the LOU between original and rearranged pairs; (3) unitization at encoding could support familiarity-based associative recognition, while unitization at retrieval did not. In briefly, unitization at encoding could improve associative recognition and this effect was moderated by UC, while unitization at retrieval did not affect associative recognition.

Unitization does not impede overall item recognition performance: Behavioral and event-related potential study

It is widely accepted that unitization can promote familiarity-based associative recognition, but the role of unitization in recognition of individual component elements which originate from compound words remains unclear. The goals of this study were to elaborate on how unitization affects item recognition and further examine the effect of unitization on the extent to which familiarity and recollection contribute to item recognition. During the study phase, participants were asked to learn 48 compound words and 48 unrelated word pairs, and during the test phase, they were instructed to distinguish old from new words. We disassociated the contribution of familiarity and recollection to recognition with remember/know paradigm in experiment 1 and with ERPs old/new effects in experiment 2. The results showed that the overall item recognition was equivalent between the two retrieval conditions. Disassociation the contribution of familiarity and recollection, we found that there was higher recollection-based item recognition performance for compound-old words than for unrelated-old words in experiment 1. In contrast, in experiment 2, the magnitude of later parietal old/new effect related to recollection was larger for the former than for the latter, indicating that equivalent levels of memory retrieval were achieved through "less" neural correlates of familiarity and recollection. By synthesizing the results of experiment 1 and 2, we believed unitization did not impede overall item recognition performance.

The effect of unitization on associative recognition was not moderated by the unitization-congruence between original and rearranged picture pairs (UC) for picture stimuli

It is widely accepted that associative recognition can be supported by familiarity through integrating more than two stimuli into a unit, but the role of unitization in recollection-based associative recognition remains unclear. In this study, we aimed to illustrate how the level of unitization (LOU) affected recollection-based associative recognition and to examine whether the unitization-congruence between original and rearranged picture pairs (UC) could have effect on the relationship between LOU and associative recognition. In encoding, participants were asked to learn related and unrelated picture pairs, and in retrieval, they needed to distinguish intact pairs from rearranged pairs. We also distinguished the LOU of the pairs based on its status at encoding or retrieval separately. The results showed that: (1) LOU-at-encoding could improve associative recognition through increasing recollection-based associative recognition selectively; (2) LOU-at-retrieval could improve associative recognition through increasing familiarity-based and recollection-based associative recognitions; (3) UC did not moderate the relationship between LOU and associative recognition. Hence, in future studies, researchers do not need to pay much attention to the construction of rearranged pairs to ensure that the LOU between original and rearranged picture pairs is matched. It greatly reduces the difficulty of materials selection.

Unitization modulates recognition of within-domain and cross-domain associations: Evidence from event-related potentials

Although it is often assumed that memory of episodic associations requires recollection, it has been suggested that, when stimuli are experienced as a unit, earlier memory processes might contribute to their subsequent associative recognition. We investigated the effects of associative relations and perceptual domain during episodic encoding on the ability to utilize early memory processes to retrieve associative information. During the study phase, participants encoded compound and noncompound words pairs, presented either to the same sensory modality (visual presentation) or to different sensory modalities (audiovisual presentation). At the test phase, they discriminated between old, rearranged, and new pairs while ERPs were recorded. In an early ERP component, differences related to associative memory emerged only for compounds, regardless of their encoding modality. These findings indicate that episodic retrieval of compound words can be supported by early-onset recognition processes regardless of whether both words were presented to the same or different sensory modalities, and suggests that unitization can operate at an abstract level, across a broad range of materials.

Dissociating neural correlates of retrieval practice and elaborative study in associative recognition memory

Retrieval practice effect refers to better long-term retention enhanced by active retrieval compared to re-studying, which has been widely demonstrated. However, controversies remain as to whether the underlying mechanism of this effect could be attributed to semantic elaboration. We investigated whether retrieval practice and elaboration were equivalent by observing the underlying cognitive processes of the two conditions using corresponding event-related potentials measures of associative memory and item memory. Behavioral results showed that retrieval practice induced better associate memory performance than elaborative study. For event-related potential results, an early old/recombined effect (FN400) related to familiarity and a late old/recombined effect (late positive component) related to recollection emerged in the retrieval practice condition, while both were absent in the elaborative study condition. An early recombined/new effect (FN400) appeared in the elaborative study condition, which did not occur in the retrieval practice condition. It could be inferred that retrieval practice promoted the recollection of episodic contexts for later associative memory, while elaborative study strengthened the familiarity of individual item. These findings suggest that retrieval practice and elaboration are two distinctive processes.

The Impact of Semantic Relatedness on Associative Memory in Aging Depending on the Semantic Relationships between the Memoranda

Background: Aging is characterized by a decline in associative memory. However, under some conditions, such as in the presence of semantic relatedness within the association, the age-related associative decline can be attenuated. In this study, we evaluated whether the nature of the semantic relationship between the memoranda (taxonomic versus thematic) could modulate the impact of semantic relatedness on older adults' associative memory. Methods: We assessed 40 young adults and 40 older adults' associative memory for associations that were either taxonomically-related, thematically-related, or unrelated. Results: While the main results showed age-related differences in all associative memory tasks without attenuation by semantic relatedness, the results after excluding 4 outlier older participants suggest that older adults' associative memory performance did not differ from that of young adults for thematically-related pairs, while there was an age-related difference in associative memory for taxonomically-related pairs as well as for unrelated pairs. Discussion: This could suggest that the nature of the semantic relationship between the memoranda can modulate the impact of semantic relatedness on older adults' associative memory performance, although the reason why this is not the case for all older participants still needs to be understood.

Associative memory for conceptually unitized word pairs in mild cognitive impairment is related to the volume of the perirhinal cortex

Unitization, that is, the encoding of an association as one integrated entity, has been shown to improve associative memory in populations presenting with associative memory deficit due to hippocampal dysfunction, such as amnesic patients with focal hippocampal lesions and healthy older adults. One reason for this benefit is that encoding of unitized associations would rely on the perirhinal cortex (PrC) and thus minimize the need for hippocampal recruitment. Mild cognitive impairment (MCI) is accompanied by a deficit in associative memory. However, unitization has never been studied to explore the potential benefit in associative memory in MCI, maybe because MCI is characterized by PrC pathology. However, the PrC may potentially still function sufficiently to allow for the successful adoption of unitization. In this study, we aimed at assessing whether unitization could attenuate MCI patients' associative memory deficit, and whether the ability to remember unitized associations would be modulated by the integrity of the PrC in MCI patients. Unitization was manipulated at a conceptual level, by encouraging participants to encode unrelated word pairs as new compound words. Participants also underwent a structural MRI exam, and measures of PrC were extracted (Brodmann Areas [BA] 35 and 36). Results showed that, contrary to healthy controls, MCI patients did not benefit from unitization. Moreover, their memory performance for unitized associations was related to the measure of PrC integrity (BA35), while it was not the case in controls. This finding thus suggests that unitization does not help to attenuate the associative deficit in MCI patients, and brings support to the literature linking unitization to the PrC function.

Evidence of relational retrieval, even in the absence of the relational eye movement effect (REME)

Eye movements indicate relational memory retrieval by disproportional viewing of a matching stimulus compared to non-matching stimuli after a pair learning study phase (the REME). Experiment 1 showed that the magnitude of the eye movement effect is linked to the subjective confidence level of the responses and we could not find evidence of the REME in incorrect responses, where participants lack conscious recollection. In experiment 2 we used a no-choice task, where participants were instructed to learn the test displays after they have completed a pair learning study phase. The REME only appeared in those participants, who could spontaneously report their relational retrieval (aware group). Meanwhile both aware and unaware participants demonstrated evidence of relational retrieval in a new eye movement measure. Taken together, we demonstrated that the REME is not necessary for retrieval and in both of our experiments the emergence of the REME was associated with conscious access.

The missing link? Testing a schema account of unitization

Unitization refers to the creation of a new unit from previously distinct items. The concept of unitization has been used to explain how novel pairings between items can be remembered without requiring recollection, by virtue of new, item-like representations that enable familiarity-based retrieval. We tested an alternative account of unitization - a schema account - which suggests that associations between items can be rapidly assimilated into a schema. We used a common operationalization of "unitization" as the difference between two unrelated words being linked by a definition, relative to two words being linked by a sentence, during an initial study phase. During the following relearning phase, a studied word was re-paired with a new word, either related or unrelated to the original associate from study. In a final test phase, memory for the relearned associations was tested. We hypothesized that, if unitized representations act like schemas, then we would observe some generalization to related words, such that memory would be better in the definition than sentence condition for related words, but not for unrelated words. Contrary to the schema hypothesis, evidence favored the null hypothesis of no difference between definition and sentence conditions for related words (Experiment 1), even when each cue was associated with multiple associates, indicating that the associations can be generalized (Experiment 2), or when the schematic information was explicitly re-activated during Relearning (Experiment 3). These results suggest that unitized associations do not generalize to accommodate new information, and therefore provide evidence against the schema account.

Impaired perceptual integration and memory for unitized representations are associated with perirhinal cortex atrophy in Alzheimer's disease

Unitization, the capacity to encode associations as one integrated entity, can enhance associative memory in populations with an associative memory deficit by promoting familiarity-based associative recognition. Patients with Alzheimer's disease (AD) are typically impaired in associative memory compared with healthy controls but do not benefit from unitization strategies. Using fragmented pictures of objects, this study aimed at assessing which of the cognitive processes that compose unitization is actually affected in AD: the retrieval of unitized representations itself, or some earlier stages of processing, such as the integration process at a perceptual or conceptual stage of representation. We also intended to relate patients' object unitization capacity to the integrity of their perirhinal cortex (PrC), as the PrC is thought to underlie unitization and is also one of the first affected regions in AD. We evaluated perceptual integration capacity and subsequent memory for those items that have supposedly been unitized in 23 mild AD patients and 20 controls. We systematically manipulated the level of perceptual integration during encoding by presenting object pictures that were either left intact, separated into 2 fragments, or separated into 4 fragments. Subjects were instructed to unitize the fragments into a single representation. Success of integration was assessed by a question requiring the identification of the object. Participants also underwent a structural magnetic resonance imaging examination, and measures of PrC, posterior cingulate cortex volume and thickness, and hippocampal volume, were extracted. The results showed that patients' perceptual integration performance decreased with the increased fragmentation level and that their memory for unitized representations was impaired whatever the demands in terms of perceptual integration at encoding. Both perceptual integration and memory for unitized representations were related to the integrity of the PrC, and memory for unitized representations was also related to the volume of the hippocampus. We argue that, globally, this supports representational theories of memory that hold that the role of the PrC is not only perceptual nor mnemonic but instead underlies complex object representation.

Misrecollection prevents older adults from benefitting from semantic relatedness of the memoranda in associative memory

Memory for episodic associations declines in aging, ostensibly due to decreased recollection abilities. Accordingly, associative unitization - the encoding of associated items as one integrated entity - may potentially attenuate age-related associative deficits by enabling familiarity-based retrieval, which is relatively preserved in aging. To test this hypothesis, we induced bottom-up unitization by manipulating semantic relatedness between memoranda. Twenty-four young and 24 older adults studied pairs of object pictures that were either semantically related or unrelated. Participants subsequently discriminated between intact, recombined and new pairs. We found that semantic relatedness increased the contributions of both familiarity and recollection in young adults, but did not improve older adults' performance. Instead, they showed associative deficits, driven by increased recollection-based false recognition. This may reflect a "misrecollection" phenomenon, in which older adults make more false alarms to recombined pairs with particularly high confidence, due to poorer retrieval monitoring regarding semantically-related associative probes.

Morphological processing in the brain: The good (inflection), the bad (derivation) and the ugly (compounding)

There is considerable behavioral evidence that morphologically complex words such as 'tax-able' and 'kiss-es' are processed and represented combinatorially. In other words, they are decomposed into their constituents 'tax' and '-able' during comprehension (reading or listening), and producing them might also involve on-the-spot combination of these constituents (especially for inflections). However, despite increasing amount of neurocognitive research, the neural mechanisms underlying these processes are still not fully understood. The purpose of this critical review is to offer a comprehensive overview on the state-of-the-art of the research on the neural mechanisms of morphological processing. In order to take into account all types of complex words, we include findings on inflected, derived, and compound words presented both visually and aurally. More specifically, we cover a wide range of electro- and magnetoencephalography (EEG and MEG, respectively) as well as structural/functional magnetic resonance imaging (s/fMRI) studies that focus on morphological processing. We present the findings with respect to the temporal course and localization of morphologically complex word processing. We summarize the observed findings, their interpretations with respect to current psycholinguistic models, and discuss methodological approaches as well as their possible limitations.

Age effects on associative memory for novel picture pairings

Normal aging is usually accompanied by greater memory decline for associations than for single items. Though associative memory is generally supported by recollection, it has been suggested that familiarity can also contribute to associative memory when stimuli can be unitized and encoded as a single entity. Given that familiarity remains intact during healthy aging, this may be one route to reducing age-related associative deficits. The current study investigated age-related differences in associative memory under conditions that were expected to differentially promote unitization, in this case by manipulating the spatial arrangement of two semantically unrelated objects positioned relative to each other in either spatially implausible or plausible orientations. Event-related potential (ERP) correlates of item and associative memory were recorded whilst younger and older adults were required to discriminate between old, recombined and new pairs of objects. These ERP correlates of item and associative memory did not vary with plausibility, whereas behavioral measures revealed that both associative and item memory were greater for spatially plausible than implausible pair arrangements. Contrary to predictions, older adults were less able to take advantage of this memory benefit than younger participants. Potential reasons for this are considered, and these are informed by those lines of evidence which indicate older participants were less sensitive to the bottom-up spatial manipulation employed here. It is recommended that future strategies for redressing age-related associative deficits should take account of the aging brain's increasing reliance on pre-existing semantic associations.

Electrophysiological Correlates of Familiarity and Recollection in Associative Recognition: Contributions of Perceptual and Conceptual Processing to Unitization

It is generally accepted that associative recognition memory is supported by recollection. In addition, recent research indicates that familiarity can support associative memory, especially when two items are unitized into a single item. Both perceptual and conceptual manipulations can be used to unitize items, but few studies have compared these two methods of unitization directly. In the present study, we investigated the effects of familiarity and recollection on successful retrieval of items that were unitized perceptually or conceptually. Participants were instructed to remember either a Chinese two-character compound or unrelated word-pairs, which were presented simultaneously or sequentially. Participants were then asked to recognize whether word-pairs were intact or rearranged. Event-related potential (ERP) recordings were performed during the recognition phase of the study. Two-character compounds were better discriminated than unrelated word-pairs and simultaneous presentation was found to elicit better discrimination than sequential presentation for unrelated word-pairs only. ERP recordings indicated that the early intact/rearranged effects (FN400), typically associated with familiarity, were elicited in compound word-pairs with both simultaneous and sequential presentation, and in simultaneously presented unrelated word-pairs, but not in sequentially presented unrelated word-pairs. In contrast, the late positive complex (LPC) effects associated with recollection were elicited in all four conditions. Together, these results indicate that while the engagement of familiarity in associative recognition is affected by both perceptual and conceptual unitization, conceptual unitization promotes a higher level of unitization (LOU). In addition, the engagement of recollection was not affected by unitized manipulations. It should be noted, however, that due to experimental design, the effects presented here may be due to semantic rather than episodic memory and future studies should take this into consideration when manipulating rearranged pairs.

The Effect of Unitizing Word Pairs on Recollection Versus Familiarity-Based Retrieval- Further Evidence From ERPs

We investigated the contribution of familiarity and recollection to associative retrieval of word pairs depending on the extent to which the pairs have been unitized through task instructions in the encoding phase. Participants in the unitization condition encoded word pairs in the context of a definition that tied them together such that they were treated as a coherent new item, while in the control condition word pairs were inserted into a sentence frame in which each word remained an individual unit. Contrasting event-related potentials (ERERPs) elicited in a subsequent recognition test by old (intact) and recombined (a new combination of two words from different study pairs) word pairs, an early frontal effect, the putative ER P correlate of familiarity-based retrieval, was apparent in the unitization condition. The left parietal old/new effect, reflecting recollection-based retrieval, was elicited only in the control condition. This suggests that in the unitization condition only, familiarity was sufficiently diagnostic to distinguish old from recombined pairs, while in the control condition, recollection contributed to associative recognition. Our findings add to a body of literature suggesting that unitization of associations increases the relative contribution of familiarity to subsequent associative retrieval.