Task Demands Differentially Affect Processing of Intrinsic and Extrinsic Object Features in Working Memory

Some argue that visual working memory operates on integrated object representations. Here, we contend that obligatory feature integration occurs with intrinsic but not extrinsic object features. Working memory for shapes and colors was assessed using a change-detection task with a central test probe, while recording event-related potentials (ERPs). Color was either an intrinsic surface feature of a shape or connected to the shape via a proximal but spatially disjunct extrinsic frame. There were two types of test: The direct test required memory for shape and color; the indirect test required only shape memory. Study-test changes of color were therefore either task-relevant or task-irrelevant. We assessed performance costs and event-related potential (ERP) effects arising from color changes. In the direct test, performance was poorer for extrinsic than intrinsic stimuli; task-relevant color changes elicited enhanced frontal negativity (N2, FN400) for both intrinsic and extrinsic stimuli. In the indirect test, performance costs and ERP effects associated with irrelevant color change were larger for intrinsic than extrinsic stimuli. This suggests intrinsic information is more readily integrated into the working-memory representation and evaluated against the test probe. Findings imply that feature integration is not obligatory under all conditions but influenced by stimulus-driven and task-related focus of attention.

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.

Visual Working Memory of Chinese Characters and Expertise: The Expert's Memory Advantage Is Based on Long-Term Knowledge of Visual Word Forms

People unfamiliar with Chinese characters show poorer visual working memory (VWM) performance for Chinese characters than do literates in Chinese. In a series of experiments, we investigated the reasons for this expertise advantage. Experiments 1 and 2 showed that the advantage of Chinese literates does not transfer to novel material. Experts had similar resolution as novices for material outside of their field of expertise, and the memory of novices and experts did not differ when detecting a big change, e.g., when a character’s color was changed. Memorizing appears to function as a rather abstract representation of word forms because memory for characters’ fonts was poor independently of expertise (Experiment 3), though still visual. Distractors that were highly similar conceptually did not increase memory errors, but visually similar distractors impaired memory (Experiment 4). We hypothesized that literates in Chinese represent characters in VWM as tokens of visual word forms made available by long-term memory. In Experiment 5, we provided novices with visual word form knowledge. Participants subsequently performed a change detection task with trained and novel characters in a functional magnetic resonance experiment. We analyzed set size- and training-dependent effects in the intraparietal sulcus (IPS) and the visual word form area. VWM for trained characters was better than for novel characters. Neural activity increased with set size and at a slower rate for trained than for novel characters. All conditions approached the same maximum, but novel characters reached the maximum at a smaller set size than trained characters. The time course of the bold response depended on set size and knowledge status. Starting from the same initial maximum, neural activity at small set sizes returned to baseline more quickly for trained characters than for novel characters. Additionally, high performers showed generally more neural activity in the IPS than low performers. We conclude that experts’ better performance in working memory (WM) is caused by the availability of visual long-term representations (word form types) that allow a sparse representation of the perceived stimuli and make even small changes big because they cause a type change that is easily detected.

Spatio-Temporal Neural Changes After Task-Switching Training in Old Age

In the present study, we aimed at examining selective neural changes after task-switching training in old age by not only considering the spatial location but also the timescale of brain activation changes (i.e., sustained/block-related or transient/trial-related timescales). We assigned a sample of 50 older adults to a task-switching training or an active single-task control group. We administered two task paradigms, either sensitive to transient (i.e., a context-updating task) or sustained (i.e., a delayed-recognition working-memory task) dynamics of cognitive control. These dynamics were captured by utilizing an appropriate event-related or block-related functional magnetic resonance imaging design. We captured selective changes in task activation during the untrained tasks after task-switching training compared to an active control group. Results revealed changes at the neural level that were not evident from only behavioral data. Importantly, neural changes in the transient-sensitive context updating task were found on the same timescale but in a different region (i.e., in the left inferior parietal lobule) than in the task-switching training task (i.e., ventrolateral PFC, inferior frontal junction, superior parietal lobule), only pointing to temporal overlap, while neural changes in the sustained-sensitive delayed-recognition task overlapped in both timescale and region with the task-switching training task (i.e., in the basal ganglia), pointing to spatio-temporal overlap. These results suggest that neural changes after task-switching training seem to be critically supported by the temporal organization of neural processing.

The impact of perceptual changes to studied items on ERP correlates of familiarity and recollection is subject to hemispheric asymmetries

It is still unclear which role the right hemisphere (RH) preference for perceptually specific and the left hemisphere (LH) bias towards abstract memory representations play at the level of episodic memory retrieval. When stimulus characteristics hampered the retrieval of abstract memory representations, these hemispheric asymmetries have previously only modulated event-related potential (ERP) correlates of recollection (late positive complex, LPC), but not of familiarity (FN400). In the present experiment, we used stimuli which facilitated the retrieval of abstract memory representations. With the divided visual field technique, new items, identical repetitions and color-modified versions of incidentally studied object pictures were presented in either the right (RVF) or the left visual field (LVF). Participants performed a memory inclusion task, in which they had to categorize both identically repeated and color-modified study items as 'old'. Only ERP, but not behavioral data showed hemispheric asymmetries: Compared to identical repetitions, FN400 and LPC old/new effects for color-modified items were equivalent with RVF/LH presentation, but reduced with LVF/RH presentation. By promoting the use of abstract stimulus information for memory retrieval, we were thus able to show that hemispheric asymmetries in accessing abstract or specific memory representations can modulate ERP correlates of familiarity as well as recollection processes.

Is the Correlation between Storage Capacity and Matrix Reasoning Driven by the Storage of Partial Solutions? A Pilot Study of an Experimental Approach

Working memory capacity (WMC) and reasoning abilities-as assessed by figural matrices tests-are substantially correlated. It is controversially discussed whether this correlation is only caused by controlled attention or also by storage capacity. This study aims at investigating storage of partial solutions as a possible mechanism by which storage capacity may contribute to solving figural matrices tests. For this purpose, we analyzed how an experimental manipulation of storage demands changes the pattern of correlations between WMC and performance in a matrix task. We manipulated the storage demands by applying two test formats: one providing the externalization of partial solutions and one without the possibility of externalization. Storage capacity was assessed by different types of change detection tasks. We found substantial correlations between storage capacity and matrices test performance, but they were of comparable size for both test formats. We take this as evidence that the necessity to store partial solutions is not the limiting factor which causes the association between storage capacity and matrices test. It is discussed how this approach can be used to investigate alternative mechanisms by that storage may influence performance in matrices tests.

Recollection is delayed under changed viewing conditions: A graded effect on the latency of the late posterior component

Object recognition is a central human ability. In everyday life, the conditions under which objects have to be recognized are usually not perfect. Often, viewing conditions change in between two encounters with an object; typical are changes in illumination or in the object-observer distance. With such changes, object recognition sometimes feels slightly delayed. We examined this phenomenon empirically by measuring the latency of the well-established electrophysiological correlate of recollection, the late posterior component (LPC), in an object-recognition task. Although the cognitive processes underlying successful recognition are well examined, thus far the consequences of changed viewing conditions on the timing of these processes have not been investigated. The ERP technique is well suited for investigating this question, because it allows differentiating between processes contributing to recognition times (in particular, recollection from familiarity as indexed by the FN400 component) and measuring their time course with high temporal precision. In the present study, participants' task was to differentiate previously studied (old) objects from a set of new objects. Viewing conditions for old objects changed slightly, changed strongly, or remained identical between learning and test. We found that the latency of the LPC in response to an old object was delayed whenever viewing conditions changed. Moreover, this delay in LPC latency scaled with the size of the change. These effects were absent for the FN400. This is the first examination of effects of changes in viewing conditions on the latency of recollection and the first dissociation of FN400 and LPC latencies.

ERP evidence for hemispheric asymmetries in abstract but not exemplar-specific repetition priming

Implicit memory retrieval is thought to be exemplar-specific in the right hemisphere (RH) but abstract in the left hemisphere (LH). Yet, conflicting behavioral priming results illustrate that the level at which asymmetries take effect is difficult to pinpoint. In the present divided visual field experiment, we tried to address this issue by analyzing ERPs in addition to behavioral measures. Participants made a natural/artificial decision on lateralized visual objects that were either new, identical repetitions, or different exemplars of studied items. Hemispheric asymmetries did not emerge in either behavioral or late positive complex (LPC) priming effects, but did affect the process of implicit memory retrieval proper as indexed by an early frontal negativity (N350/(F)N400). Whereas exemplar-specific N350/(F)N400 priming effects emerged irrespective of presentation side, abstract implicit memory retrieval of different exemplars was contingent on right visual field presentation and the ensuing initial stimulus processing by the LH.

The beneficial effect of testing: an event-related potential study

The enhanced memory performance for items that are tested as compared to being restudied (the testing effect) is a frequently reported memory phenomenon. According to the episodic context account of the testing effect, this beneficial effect of testing is related to a process which reinstates the previously learnt episodic information. Few studies have explored the neural correlates of this effect at the time point when testing takes place, however. In this study, we utilized the ERP correlates of successful memory encoding to address this issue, hypothesizing that if the benefit of testing is due to retrieval-related processes at test then subsequent memory effects (SMEs) should resemble the ERP correlates of retrieval-based processing in their temporal and spatial characteristics. Participants were asked to learn Swahili-German word pairs before items were presented in either a testing or a restudy condition. Memory performance was assessed immediately and 1-day later with a cued recall task. Successfully recalling items at test increased the likelihood that items were remembered over time compared to items which were only restudied. An ERP subsequent memory contrast (later remembered vs. later forgotten tested items), which reflects the engagement of processes that ensure items are recallable the next day were topographically comparable with the ERP correlate of immediate recollection (immediately remembered vs. immediately forgotten tested items). This result shows that the processes which allow items to be more memorable over time share qualitatively similar neural correlates with the processes that relate to successful retrieval at test. This finding supports the notion that testing is more beneficial than restudying on memory performance over time because of its engagement of retrieval processes, such as the re-encoding of actively retrieved memory representations.

ERP evidence for hemispheric asymmetries in exemplar-specific explicit memory access

The right cerebral hemisphere (RH) appears to be more effective in representing visual objects as distinct exemplars than the left hemisphere (LH) which is presumably biased towards coding objects at the level of abstract prototypes. As of yet, relatively little is known about the role that asymmetries in exemplar-specificity play at the level of explicit memory retrieval. In the present study, we addressed this issue by examining hemispheric asymmetries in the putative event-related potential (ERP) correlates of familiarity (FN400) and recollection (LPC). In an incidental study phase, pictures of familiar objects were presented centrally. At test, participants performed a memory inclusion task on identical repetitions and different exemplars of study items as well as new items which were presented in only one visual hemifield using the divided visual field technique. With respect to familiarity, we observed exemplar-specific FN400 old/new effects that were more pronounced for identical repetitions than different exemplars, irrespective of the hemisphere governing initial stimulus processing. In contrast, LPC old/new effects were subject to some hemispheric asymmetries indicating that exemplar-specific recollection was more extensive in the RH than in the LH. This further corroborates the idea that hemispheric asymmetries should not be generalized but need to be distinguished not only in different domains but also at different levels of processing.

Individual differences in working memory capacity and attentional control

Visual working memory (WM) has a very limited online capacity making it considerably important to control the gating of encoding into WM. Recent studies have suggested that attention control is of importance in doing so, especially the time needed to disengage. However, the disengagement mechanism operates on a later stage of processing after the initial selection of information has already been initiated. We assume that individual differences in WM capacity are also driven by individual variations in the voluntary engagement of attention. In 2 experiments we investigated whether individuals with high- and low-WM capacity differ in the efficiency and speed of this attention control process. We realised different versions of the task in which different amounts of attention control were necessary, a more automatically triggered allocation of attention and a voluntary initiation of attention engagement, respectively. We further manipulated the time course to look for differences in the latency of attention control. The results revealed that participants with low-WM capacity were less effective to exhibit voluntary attention control processes and they were also slower in doing so compared with high-WM capacity individuals. However, this effect seems to be partly moderated by the ability to update the current task set. If the trial structure did not require task set updating smaller individual differences involving WM capacity could be found.

Effects of short-term experience on anticipatory eye movements during action observation

Recent studies have shown that anticipatory eye movements occur during both action observation and action execution. These findings strongly support the direct matching hypothesis, which states that in observing others' actions, people take advantage of the same action knowledge that enables them to perform the same actions. Furthermore, a connection between action experience and the ability to anticipate action goals has been proposed. Concerning the role of experience, most studies concentrated on motor experts such as athletes and musicians, whereas only few studies investigated whether motor programs can be activated by short-term experience. Applying a pre-post design, we examined whether short-term experience affects anticipatory eye movements during observation. Participants (N = 150 university students) observed scenes showing an actor performing a block stacking task. Subsequently, participants performed either a block stacking task, puzzles, or a pursuit rotor task. Afterward, participants were again provided with the aforementioned block stacking task scenes. Results revealed that the block stacking task group directed their gaze significantly earlier toward the action goals of the block stacking task during posttest trials, compared with Puzzle and pursuit rotor task groups, which did not differ from each other. In accordance with the direct matching hypothesis, our study provides evidence that short-term experience with the block stacking task activates task-specific action knowledge.

Intercommunication Between Prefrontal and Posterior Brain Regions for Protecting Visual Working Memory From Distractor Interference

Because visual working memory has a very restricted capacity, good filtering mechanisms are essential for its successful functioning. A neuronal signal emitted by the prefrontal cortex is considered to be an important contributor to filtering. Proof of the functional significance of this signal during normal cognitive functioning is, however, still missing. Furthermore, research has so far neglected that the prefrontal cortex must receive input from posterior brain areas that report the necessity to filter. From human electroencephalograms, we extracted several event-related components that reflect the different subprocesses of filtering. On the basis of their timing and a clear pattern of correlations, we reason that filtering might consist of a causal chain of events that involve prefrontal and posterior cortex regions: After distractors are detected in posterior regions, a prefrontal mechanism is activated, which in turn prevents subsequent unnecessary parietal storage of distractor information.

Culture-specific familiarity equally mediates action representations across cultures

Previous studies have shown that we need to distinguish between means and end information about actions. It is unclear how these two subtypes of action information relate to each other with theoretical accounts postulating the superiority of end over means information and others linking separate means and end routes of processing to actions of differential meaningfulness. Action meaningfulness or familiarity differs between cultures. In a cross-cultural setting, we investigated how action familiarity influences recognition memory for means and end information. Object directed actions of differential familiarity were presented to Chinese and German participants. Action familiarity modulated the representation of means and end information in both cultures in the same way, although the effects were based on different stimulus sets. Our results suggest that, in the representation of actions in memory, end information is superordinate to means information. This effect is independent of culture whereas action familiarity is not.

Gains of item-specific training in visual working memory and their neural correlates

Experts sometimes show higher working memory performance than novices but contrary to this finding, evidence for a positive effect of item-specific training is rare. This study provides evidence for item-specific training gains. We presented Chinese characters and artificial patterns (spotted figures) in a change detection task before and after training (varying set size from 1 to 3). A part of the Chinese characters were trained; others and the spotted figures were not trained. Memory capacity was between one and two items. For set size two, memory performance for trained characters was higher than for untrained characters and they were processed faster. Within superior intraparietal sulcus and middle occipital cortex (part of the putative posterior working memory network), the neural activity asymptotically increased with set size. Untrained items reached the activation maximum already at set size two. For this set size, the activity was significantly reduced for trained items so that a further increase from two to three items was observed. We interpret this difference as a correlate of a gain in neural efficiency. The size of this difference correlated with the training gain in memory. We assume that training causes a more efficient neural representation of trained items supported by long-term memory and this allows holding more items in working memory.

Navigation assistance: a trade-off between wayfinding support and configural learning support

Current GPS-based mobile navigation assistance systems support wayfinding, but they do not support learning about the spatial configuration of an environment. The present study examined effects of visual presentation modes for navigation assistance on wayfinding accuracy, route learning, and configural learning. Participants (high-school students) visited a university campus for the first time and took a predefined assisted tour. In Experiment 1 (n = 84, 42 females), a presentation mode showing wayfinding information from eye-level was contrasted with presentation modes showing wayfinding information included in views that provided comprehensive configural information. In Experiment 2 (n = 48, 24 females), wayfinding information was included in map fragments. A presentation mode which always showed north on top of the device was compared with a mode which rotated according to the orientation of the user. Wayfinding accuracy (deviations from the route), route learning, and configural learning (direction estimates, sketch maps) were assessed. Results indicated a trade-off between wayfinding and configural learning: Presentation modes providing comprehensive configural information supported the acquisition of configural knowledge at the cost of accurate wayfinding. The route presentation mode supported wayfinding at the cost of configural knowledge acquisition. Both presentation modes based on map fragments supported wayfinding. Individual differences in visual-spatial working memory capacity explained a considerable portion of the variance in wayfinding accuracy, route learning, and configural learning. It is concluded that learning about an unknown environment during assisted navigation is based on the integration of spatial information from multiple sources and can be supported by appropriate visualization.

What Does Ipsilateral Delay Activity Reflect? Inferences from Slow Potentials in a Lateralized Visual Working Memory Task

In the lateralized change detection task, two item arrays are presented, one on each side of the display. Participants have to remember the items in the relevant hemifield and ignore the items in the irrelevant hemifield. A difference wave between contralateral and ipsilateral slow potentials with respect to the relevant items, the contralateral delay activity, can be calculated. As its amplitude varies with the number of items held in working memory (WM) and reaches its asymptote with WM capacity, it is considered a pure neural correlate of visual WM load. However, in addition to this contralateral delay activity, load-dependent activity has also been observed over the hemisphere ipsilateral to the relevant hemifield, suggesting that the ipsilateral hemisphere is also involved in memory-related processes. This ipsilateral activity might either reflect a bilateral processing of relevant or else a lateralized processing of irrelevant, to-be-filtered-out items. As in the lateralized change detection task, the number of items on both sides of the display is typically identical, it was not possible to decide between these alternatives yet. To disentangle the influence of relevant and irrelevant items, we orthogonally varied the number of both types of items. Processing of relevant items caused purely contralateral load-dependent activity. Ipsilateral slow potentials were influenced by the number of irrelevant items only if visual WM load was low, but not if it was high. This suggests that whether irrelevant items are processed or filtered out depends on visual WM load.

The influence of expertise and of physical complexity on visual short-term memory consolidation

We investigated whether the expertise of a perceiver and the physical complexity of a stimulus influence consolidation of visual short-term memory (VSTM) in a S1–S2 (Stimulus 1–Stimulus 2) change detection task. Consolidation is assumed to make transient perceptual representations in VSTM more durable, and it is investigated by postexposure of a mask shortly after offset of the perceived stimulus (S1; 17 to 483 ms). We presented colours, Chinese characters, pseudocharacters, and novel symbols to novices (Germans) or experts of Chinese language (Chinese readers). Physical complexity was manipulated by the number of strokes. Unfamiliar material was remembered worse than familiar material (Experiments 1, 2, and 3). For novices the absolute VSTM performance was better for physically simple than for complex material, whereas for experts the complexity did not matter—Chinese readers memorized Chinese characters (Experiment 3). Articulatory suppression did not change these effects (Experiment 2). We always observed a strong effect of SOA, but this effect was influenced neither by physical complexity nor by expertise; only the length of the interstimulus interval between S1 and the mask was relevant. This was observed even with short stimulus onset asynchrony (SOA) of 100 ms (Experiment 2) and in comparing colours and characters (Experiment 5). However, masks impaired memory if they were presented at the locations of the to-be-memorized items, but not beside them—that is, interference was location-based (Experiment 6). We explain the effect of SOA by the assumption that it takes time to stop encoding of information presented at item locations with the offset of S1. The increasing resistance against interference by irrelevant material appears as consolidation of S1.

fMRI correlates of working memory: specific posterior representation sites for motion and position information

We assume that working memory is provided by a network comprising domain-general anterior and different domain-specific posterior brain areas depending on the type of stimulus and the task demands. Based on imaging studies from perception, we hypothesized that dynamic spatial (motion) and static spatial (position) information can be dissociated during retention in working memory. Participants were presented with a moving dot. About one second after stimulus presentation, a cue indicated whether its motion or end position should be held in memory. Six seconds later, a second stimulus was shown which was to be compared with the first one with respect to identity on the cued dimension. In the baseline condition, the cue indicated that no memory task would follow. We contrasted activity during maintenance of the different features. Differential activations in regions related to motion perception (area hMT/V5+, superior temporal sulcus) were observed in the motion working memory task. For position working memory, enhanced activations in a right brain region at the temporo-parieto-occipital junction emerged. The results are discussed with respect to domain-specific regions active in perception and how they can be also involved in short term retention for those very features. It is suggested that two types of spatial information categories can be dissociated: dynamic spatial (motion) and static spatial (position) information seem to be processed by different working memory structures.

The advantage of mentally rotating clockwise

The time taken to decide whether a character is shown in its mirror or normal version has been shown to increase approximately linearly with the angular departure from an up-right position. Additionally, in some studies, decisions took longer for clockwise tilted characters than for counterclockwise tilted ones. Other studies do not report the latter effect. We argue that inconsistencies across studies are caused by variance in participants' strategies. The task employed here was specifically designed to bring these strategies and thereby the direction of rotation under experimental control. From the EEG recorded during the rotation period, we extracted an event-related slow potential whose amplitude is sensitive to the amount of mental rotation. In both strategy conditions, the slow potential's amplitude was lower for clockwise than for counterclockwise rotations. We take this as evidence that mental rotation of alphanumeric characters is easier in a clockwise than in a counterclockwise direction.

Remembering perceptual features unequally bound in object and episodic tokens: Neural mechanisms and their electrophysiological correlates

We present a neurocognitive model of long-term object memory. We propose that perceptual priming and episodic recognition are phenomena based on three distinct kinds of representations. We label these representations types and tokens. Types are prototypical representations needed for object identification. The network of non-arbitrary features necessary for object categorization is sharpened in the course of repeated identification, an effect that we call type trace and which causes perceptual priming. Tokens, on the other hand, support episodic recognition. Perirhinal structures are proposed to bind intrinsic within-object features into an object token that can be thought of as a consolidated perceptual object file. Hippocampal structures integrate object- with contextual information in an episodic token. The reinstatement of an object token is assumed to generate a feeling of familiarity, whereas recollection occurs when the reinstatement of an episodic token occurs. Retrieval mode and retrieval orientation dynamically modulate access to these representations. In this review, we apply the model to recent empirical research (behavioral, fMRI, and ERP data) including a series of studies from our own lab. We put specific emphasis on the effects that sensory features and their study-test match have on familiarity. The type-token approach fits the data and additionally provides a framework for the analysis of concepts like unitization and associative reinstatement.

Visuell-räumliches Arbeitsgedächtnis

Zusammenfassung. In der Multikomponentenkonzeption des Arbeitsgedächtnisses wird explizit eine separate visuelle Teilkomponente postuliert, die in einen Speicher für statische visuelle Informationen (Visual Cache) und einen dynamischen (räumlichen) Wiederholungsprozess (Inner Scribe) unterteilt wird. In der vorliegenden Arbeit wird argumentiert, dass eine solche Aufteilung begrifflich unscharf und nicht geeignet ist, die empirischen Befunde angemessen zu erklären. Die Unterscheidung statisch versus dynamisch trifft nicht die richtige Dimension. Stattdessen sprechen neurowissenschaftliche Befunde eher für eine Trennung zwischen räumlich und visuell, wobei die räumliche Komponente zum Teil supramodal ist, während die visuelle Komponente eine Binnendifferenzierung entlang den repräsentierten Inhalten aufweist. Es wird die These aufgestellt, dass kein separater Speicher postuliert werden muss, um die in der Literatur dokumentierten Phänomene zu erklären. Die Annahme von temporär im visuellen Wahrnehmungsprozess entstehenden Repräsentationen reicht aus, um kurzzeitiges Erinnern zu erklären. Folglich wird das Arbeitsgedächtnis im gleichen verteilten neuronalen Netzwerk realisiert, das die visuelle Informationsverarbeitung in der Wahrnehmung leistet.

ERP Evidence for Flexible Adjustment of Retrieval Orientation and Its Influence on Familiarity

The assumption was tested that familiarity memory as indexed by a mid-frontal ERP old–new effect is modulated by retrieval orientation. A randomly cued category-based versus exemplar-specific recognition memory test, requiring flexible adjustment of retrieval orientation, was conducted. Results show that the mid-frontal ERP old–new effect is sensitive to the manipulation of study-test congruency—that is, whether the same object is repeated identically or a different category exemplar is presented at test. Importantly, the effect pattern depends on subjects' retrieval orientation. With a specific orientation, only same items elicited an early old–new effect (same > different = new), whereas in the general condition, the old–new effect was graded (same > different > new). This supports the view that both perceptual and conceptual processes can contribute to familiarity memory and demonstrates that the rather automatic process of familiarity is not only data driven but influenced by top–down retrieval orientation, which subjects are able to adjust on a flexible basis.

Visual and spatial working memory: from boxes to networks

It is shown that visuo-spatial working memory is better characterized as processes operating on sensory information (visual appearance) and on spatial location (environmental coordinates) in a distributed network than as unitary slave system. Results from passive (short-term) and active memory tasks (imagery) disclose the properties (capacity, content) and the components of this network. The prefrontal cortex is a control structure (dorsal prefers active, ventral passive tasks) and it contributes to spatial memory by a prospective spatial code (eye movements). Visual appearance (including dynamic aspects) is represented as features and object files (bound features) within content-specific areas in the ventral occipital cortex. Spatial coordinates are represented in the parietal cortex (modality-unspecific), when used in spatio-temporal tasks (Corsi) they are closely related to attention. Imagery of objects activates occipito-temporal structures, spatial transformations and mental rotation the parietal cortex (specifically the intraparietal sulcus). Perception, working memory, and imagery use the same neural network. Differences between the tasks are explained by different demands and states of the neural network, and differences in the configuration of the anterior-posterior neural circuits.

The influence of object and background color manipulations on the electrophysiological indices of recognition memory

In a recognition memory experiment, the claim was tested that intrinsic object features contribute to familiarity, whereas extrinsic context features do not. We used the study-test manipulation of color to investigate the perceptual specificity of ERP old-new effects associated with familiarity and recollection. Color was either an intrinsic surface feature of the object or a feature of the surrounding context (a frame encasing the object); thus, the same feature was manipulated across intrinsic/extrinsic conditions. Subjects performed a threefold (same color/different color/new object) decision, making feature information task-relevant. Results suggest that the intrinsic manipulation of color affected the mid-frontal old-new effect associated with familiarity, while this effect was not influenced by extrinsic manipulation. This ERP pattern could not be explained by basic behavioral performance differences. It is concluded that familiarity can be perceptually specific with regard to intrinsic information belonging to the object. The putative electrophysiological signature of recollection - a late parietal old-new effect - was not present in the data, and reasons for this null effect are discussed.

Modes of memory: early electrophysiological markers of repetition suppression and recognition enhancement predict behavioral performance

Different forms of perceptual memory have opposite physiological effects. Whereas repetition priming often leads to suppression of brain responses, explicit recognition has been found to enhance brain activity. We investigated effects of repetition priming and recognition memory on early gamma-band responses. In a study phase, participants performed a visual discrimination task with task-irrelevant item repetitions. Stimulus repetition suppressed early evoked gamma responses in participants with strong behavioral repetition effects. In a test phase, participants discriminated old from new items. Evoked and induced gamma activity was enhanced for old items. Effects were stronger in participants with better recognition performance. The results demonstrate a modulation of earliest stages of visual information processing by different memory systems, which is dependent on retrieval intention and predicts individual behavioral performance.

Modality and domain specific components in auditory and visual working memory tasks

In the tripartite model of working memory (WM) it is postulated that a unique part system-the visuo-spatial sketchpad (VSSP)-processes non-verbal content. Due to behavioral and neurophysiological findings, the VSSP was later subdivided into visual object and visual spatial processing, the former representing objects' appearance and the latter spatial information. This distinction is well supported. However, a challenge to this model is the question how spatial information from non-visual sensory modalities, for example the auditory one, is processed. Only a few studies so far have directly compared visual and auditory spatial WM. They suggest that the distinction of two processing domains--one for object and one for spatial information--also holds true for auditory WM, but that only a part of the processes is modality specific. We propose that processing in the object domain (the item's appearance) is modality specific, while spatial WM as well as object-location binding relies on modality general processes.

Context effects on familiarity are familiarity effects of context — An electrophysiological study

Within dual-process accounts of recognition memory, familiarity (as opposed to recollection) is often referred to as a rather automatic and context-free process. Thus, in episodic object recognition, familiarity and its electrophysiological ERP signature are supposed to index prior occurrence of an object independent of the context the object was originally encountered in, e.g., [Ecker, U.K.H., Zimmer, H.D., Groh-Bordin, C., in press. Color and context: An ERP study on intrinsic and extrinsic feature binding in episodic memory. Mem. Cogn.]). Yet, contextual sensitivity of familiarity has also been reported (e.g., [Tsivilis, D., Otten, L.J., Rugg, M.D., 2001. Context effects on the neural correlates of recognition memory: An electrophysiological study. Neuron 31, 497-505.]). We argue that considering attentional and perceptual factors of target processing is vital in understanding these conflicting results. Presenting target objects on contextual landscape scenes, we introduced a cueing technique designed to focus subjects' attention on target processing. We demonstrate that context effects on familiarity are diminished if the attentional impact of contextual stimuli is experimentally controlled, arguing that contextual influences on object familiarity are indirect and mediated by factors such as salience and attentional capture. Results suggest that salient context stimuli may elicit an independent familiarity signal instead of directly impacting on the familiarity signal of the target object. We conclude that (a) object familiarity is in principle a rather automatic and context-free process, and that (b) the study of episodic memory can profit substantially from adopting a dynamic processing perspective.

Has the butcher on the bus dyed his hair? When color changes modulate ERP correlates of familiarity and recollection

Recognition memory is usually thought of as comprising two distinct memory processes, namely familiarity and recollection. This distinction is reflected in specific event-related potential (ERP) components associated with both subprocesses. A mid-frontal attenuated negativity for correctly recognized old items relative to new ones around 400 ms has been typically linked to familiarity, whereas a parietally accentuated, more pronounced positivity for old items from 500 to 800 ms has been connected with recollection. Recently, this classification has been challenged by relating the mid-frontal old/new effect to conceptual priming mechanisms. Moreover, the perceptual sensitivity of both old/new effects is still under debate. The present study used a recognition memory task for visual objects and nonsense figures in order to investigate the functional significance of both ERP old/new effects. With respect to study presentation, all items were either presented in a perceptually identical or a color-modified version at test. Old nonsense figures, despite being meaningless, elicited a reliable mid-frontal old/new effect, thereby strongly suggesting a close relationship to familiarity processes rather than conceptual priming. Additionally, both the mid-frontal and the parietal old/new effect for real objects were graded with respect to the perceptual similarity between study and test. We argue that not only recollection, but also familiarity processes can provide information about perceptual atttributes, which is used in the course of recognition memory decisions.

Auditory and visual spatial working memory

A series of experiments compared short-term memory for object locations in the auditory and visual modalities. The stimulus materials consisted of sounds and pictures presented at different locations in space. Items were presented in pure- or mixed-modality lists of increasing length. At test, participants responded to renewed presentation of the objects by indicating their original position. If two independent modality-specific and resource-limited short-term memories support the remembering of locations, memory performance should be higher in the mixed-modality than in the pure-modality condition. Yet, memory performance was the same for items in both types of list. In addition, responses to the memory load manipulation in both modalities showed very similar declines in performance. The results are interpreted in terms of object files binding object and location information in episodic working memory, independently of the input modality.

Feature binding in perceptual priming and in episodic object recognition: evidence from event-related brain potentials

It is argued that explicit remembering is based on so-called episodic tokens binding together all perceptual features of a visual object. In episodic recognition, these features are collectively reactivated. In support of this view, it has been shown that changing sensory features of a stimulus from study to test decreases subject's performance in an episodic recognition task, even though the changed features are irrelevant for the recognition judgment. On the other hand, repetition priming is unaffected by such manipulations of perceptual specificity. Implicit memory performance is therefore thought to depend on structural representations, so-called types, comprising only invariant perceptual features, but no exemplar-specific details. Event-related potentials (ERPs) in our study revealed electrophysiological evidence for the differential involvement of these perceptual memory traces in explicit and implicit memory tasks. Participants attended either a living-nonliving task or an episodic recognition task with visually presented objects. During test both groups of participants processed new objects and old objects, which were repeated either identically or in a mirror-reversed version. In the implicit task ERPs showed an occipitoparietal repetition effect, which was the same for identically repeated items and mirror reversals. In contrast, in the explicit task an early mid-frontal old/new effect for identical but not for mirror-reversed old objects was observed indicating involuntary access to perceptual information during episodic retrieval. A later portion of the old/new effect solely differentiated both types of old items from new ones.

Differential relational encoding of categorical information in memory for action events

Memory for action phrases is better if the actions are enacted in subject-performed tasks (SPTs) than if they are only listened to in verbal tasks (VTs). This effect is ascribed to better item-specific encoding of SPTs than of VTs. The role of interitem relational information is controversial, and the findings of clustering with categorically structured lists are inconsistent (see Engelkamp, 1998). The present study contributes to clarifying these effects by demonstrating that intentional relational encoding can be used more efficiently in VTs than in SPTs and influences the degree of clustering. If the list structure is not obvious, inducing intentional encoding by presenting the category labels prior to list presentation and asking subjects to use this preinformation increases clustering in VTs but not in SPTs. Without preinformation, clustering scores of VTs and SPTs did not differ, with preinformation, clustering of VTs was stronger than that of SPTs. The authors suggest how the inconsistent findings with regard to clustering effects can be explained.

The spatial mismatch effect is based on global configuration and not on perceptual records within the visual cache

If configurations of objects are presented in a S1-S2 matching task for the identity of objects a spatial mismatch effect occurs. Changing the (irrelevant) spatial layout lengthens response times. We investigated what causes this effect. We observed a reliable mismatch effect that was not influenced by a secondary task during maintenance. Neither articulatory suppression (Experiment 1), nor unattended (Experiments 2 and 6) or attended visual material (Experiment 3) reduced the effect, and this was independent of the length of the retention interval (Experiment 6). The effect was also rather independent of the visual appearance of the local elements. It was of similar size with color patches (Experiment 4) and with completely different surface information when testing was cross modal (Experiment 5), and the name-ability of the global configuration was not relevant (Experiments 6 and 7). In contrast, the figurative similarity of the configurations of S1 and S2 systematically influenced the size of the spatial mismatch effect (Experiment 7). We conclude that the spatial mismatch effect is caused by a mismatch of the global shape of the configuration stored together with the objects of S1 and not by a mismatch of templates of perceptual records maintained in a visual cache.

Memory for actions: Item and relational information in categorized lists

Enacting action phrases in subject-performed tasks (SPTs) leads to better free recall than hearing or reading the same materials in verbal tasks (VTs). This enactment effect is usually explained by better item-specific information in SPTs than in VTs. The role of relational information is controversial. In the present paper, we will take the multiple recall approach to study the role of item and relational information in memory for actions by computing the number of item gains and the number of item losses over trials. This approach has previously been applied to lists of unrelated action phrases. We applied it to categorically related lists, also allowing a measure of relational information by clustering scores. It was found that SPTs produced more item gains than VTs. This finding confirmed the assumption that SPTs provide better item-specific information than VTs. The number of item losses did not differ between VTs and SPTs. This finding suggests that relational information is equally provided by VTs and SPTs. However, the organizational scores showed a more differentiated picture. Clustering was greater in SPTs than in VTs with randomly presented lists, but not with blocked lists. We suggested that these results, as well as other findings from the literature, could be explained by distinguishing automatic and strategic processes and the types of item associations that are addressed by these processes.

Spatio-temporal working-memory and short-term object-location tasks use different memory mechanisms

Spatial short-term memory for objects' locations was investigated in a spatial relocation task. During maintenance, dynamic visual noise or spatial tapping were administered as visual or spatial secondary tasks, respectively. Because memory for location should tap the visual component of working memory, a visual but not a spatial secondary task should impair location memory. In fact, neither of the tasks impaired memory (Experiment 1), although the expected dissociation between visual and spatial components was clearly confirmed for a spatio-temporal main task (Corsi test) (Experiment 2). We then contrasted location memory for pictures of objects and of nonsense figures under visual interference. Real objects were relocated much better than nonsense figures, and visual noise was again ineffective (Experiment 3). When spatial tapping was combined with the same material (Experiment 3a), again no influence on memory for locations of objects was observed and only a small influence on remembering nonsense figures. We suggest that the Corsi and the relocation VSWM-tasks use different memory mechanisms. The configuration of objects is reconstructed from perceptual records in an episodic buffer, provided by the same structures that enable visual memory after longer intervals. Rehearsal is not necessary for the persistence of these traces. In contrast, in the Corsi task remembering, a temporal sequence across homogeneous locations needs spatio-temporal marking and therefore active rehearsal of the locations by shifting spatial attention. A spatially demanding secondary task during retention interrupts this rehearsal.

Signing enhances memory like performing actions

In three experiments, we investigated the influence of the overt performance of signs on memory. Deaf and hearing participants studied lists of action phrases (Experiment 1) or nouns (Experiment 2) under standard verbal instruction, under the instructions to sign the verbal phrase, to symbolically perform the denoted action, or to carry out a prototypical action corresponding to each noun. Higher recall and recognition performances were observed when actions were performed than in the verbal encoding condition, and signing was as effective for memory as was enactment. Thus, overt signing can induce an enactment effect. In contrast, Experiment 3 demonstrated that performing an unrelated action did not. A unique but unrelated action was not memory efficient.

How "implicit" are implicit color effects in memory?

Processing colored pictures of objects results in a preference to choose the former color for a specific object in a subsequent color choice test (Wippich & Mecklenbräuker, 1998). We tested whether this implicit memory effect is independent of performances in episodic color recollection (recognition). In the study phase of Experiment 1, the color of line drawings was either named or its appropriateness was judged. We found only weak implicit memory effects for categorical color information. In Experiment 2, silhouettes were colored by subjects during the study phase. Performances in both the implicit and the explicit test were good. Selections of "old" colors in the implicit test, though, were almost completely confined to items for which the color was also remembered explicitly. In Experiment 3, we applied the opposition technique in order to check whether we could find any implicit effects regarding items for which no explicit color recollection was possible. This was not the case. We therefore draw the conclusion that implicit color preference effects are not independent of explicit recollection, and that they are probably based on the same episodic memory traces that are used in explicit tests.