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.

Plasticity in brain activity dynamics after task-shifting training in older adults.

Cognitive control is supported by a dynamic interplay of transient (i.e., trial-related) brain activation across fronto-parietal networks and sustained (i.e., block-related) activation across fronto-striatal networks. Older adults show disturbances in this dynamic functional recruitment. There is evidence suggesting that cognitive-control training may enable older adults to redistribute their brain activation across cortical and subcortical networks, which in turn can limit behavioral impairments. However, previous studies have only focused on spatial rather than on temporal aspects of changes in brain activation. In the present study, we examined training-related functional plasticity in old age by applying a hybrid fMRI design that sensitively tracks the spatio-temporal interactions underlying brain-activation changes. Fifty healthy seniors were assigned to a task-shifting training or an active-control group and their pretest/posttest activation-change maps were compared against 25 untrained younger adults. After training, older adults showed the same performance as untrained young adults. Compared to the control group, task-shifting training promoted proactive (i.e., early, cue-related) changes in transient mechanisms supporting the maintenance and top-down biasing of task-set representations in a specific prefrontal circuitry; reactive (i.e., late, probe-related) changes in transient mechanisms supporting response-selection processes in dissociable fronto-parietal networks; overall reductions of sustained activation in striatal circuits. Results highlight the importance of spatio-temporal interactions in training-induced neural changes in age.

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 neural mechanism of fluency-based memory illusions: the role of fluency context.

Recognition memory judgments can be influenced by a variety of signals including fluency. Here, we investigated whether the neural correlates of memory illusions (i.e., misattribution of fluency to prior study) can be modulated by fluency context. Using a masked priming/recognition memory paradigm, we found memory illusions for low confidence decisions. When fluency varied randomly across trials, we found reductions in perirhinal cortex (PrC) activity for primed trials, as well as a (pre)cuneus-PrC (BA 35) connectivity. When the fluency context was unchanging, there was increased PrC activity for primed trials, with the (pre)cuneus showing greater connectivity with PrC (BA 36). Thus, our results tentatively suggest two neural mechanisms via which fluency can lead to memory illusions.

Age-related changes in working memory: Age affects relational but not conjunctive feature binding.

In contrast to long-term memory, age-related association deficits in working memory are found only inconsistently. The authors hypothesized that type of binding is critical for the occurrence of such deficits. Relational binding abilities (associating separate visual units) should degrade with age, whereas more automatic conjunctive binding abilities (associating features within an object) should not. They contrasted associative memory and item memory using a change-detection task with colors and shapes in younger (18-33 years) and older (64-82 years) healthy adults. Color was either a surface feature of the shape (conjunctive binding) or a feature of a shape-external frame (relational binding). In a direct test of associative memory, participants memorized color-shape associations; in an indirect item memory test, participants were required to memorize only the shapes, and the authors measured the costs of ignoring task-irrelevant color changes from study to test. In the direct test, associative memory was poorer when relational binding was required rather than conjunctive binding, and associative memory was poorer in the older group, but no age-related association deficit was apparent. In the indirect test, by contrast, type of binding interacted with age: younger participants showed study-test congruence effects independent of the type of binding, but older adults showed enhanced congruence effects for conjunctive stimuli, indicating intact or even enhanced conjunctive binding, and practically no costs for relational stimuli, indicating poor relational binding. This stimulus-specific effect of a task-irrelevant feature change indicates that relational and conjunctive binding in working memory are differently affected by healthy aging. (PsycINFO Database Record

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.

Behavioural and neural evidence for the impact of fluency context on conscious memory.

It has been recently suggested that fluency may impact recognition memory performance when the fluency context varies from trial-to-trial. Surprisingly, such an effect has proved difficult to detect in the masked priming paradigm, one of the most popular means to increase fluency-based memory judgements. We conducted a functional magnetic resonance imaging (fMRI) experiment in which participants encoded words at study and, at test, performed a recognition memory task within a masked priming procedure. In order to optimise the chances of finding priming effects on recognition memory performance, we used low-frequency words, which have been shown to increase hits relative to false alarms and enhance masked priming effects. Fluency context was manipulated by either mixing primed and unprimed trials [Random context (RC) experiment] or blocking primed and unprimed trials [Blocked context (BC) experiment]. Behaviourally, priming affected high-confidence memory performance only in the RC experiment. This behavioural effect correlated positively with neural priming in several recognition memory regions. Moreover, we observed a functional coupling between the left middle temporal gyrus and the left parietal and posterior cingulate cortices that was greater for primed relative to unprimed words. In contrast, in the BC experiment, despite similar activity in recognition-memory-related regions, we did not find any significant correlations between neural and behavioural priming. Finally, we observed striking differences in the neural correlates of masked priming between the RC and BC experiments not only in location but also in direction of the neural response. Possible implications of these findings are discussed.

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.

Exploring the Cognitive Processes Causing the Age-Related Categorization Deficit in the Recognition of Facial Expressions.

BACKGROUND/STUDY CONTEXT: Elderly people do not categorize emotional facial expressions as accurately as younger people, particularly negative emotions. Although age-related impairments in decoding emotions in facial expressions are well documented, the causes of this deficit are poorly understood. This study examined the potential mechanisms that account for this age-related categorization deficit by assessing its dependence on presentation time. METHODS: Thirty young (19-27 years old) and 31 older (68-78 years old) Chinese adults were asked to categorize the six basic emotions in facial expressions, each presented for 120, 200, 600, or 1000 ms, before and after exposure to a neutral facial expression. RESULTS: Shortened presentation times caused an age-related deficit in the recognition of happy faces, whereas no deficit was observed at longer exposure times. An age-related deficit was observed for all negative emotions but was not exacerbated by shorter presentation times. CONCLUSION: Age-related deficits in categorization of positive and negative emotions are caused by different mechanisms. Because negative emotions are perceptually similar, they cause high categorization demands. Elderly people may need more evidence in favor of the target emotion than younger people, and they make mistakes if this surplus of evidence is missing. In contrast, perceptually distinct happy faces were easily identified, and elderly people only failed when the presentation time was too short for their slower perceptual processing.

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 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.

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.

Contributions of attention and elaboration to associative encoding in young and older adults.

Episodic memory declines during healthy aging, with a particular reduction in the ability to encode associations. We investigated the role of alternating attentional focus between two items of a pair in order to generate associative links, as well as working memory based elaborative processes in this age-related memory deficit. While their eye gaze behavior and ERPs were recorded, 19 young and 22 elderly (64-79 years) participants used interactive imagery to encode pairs of spatially separated objects. In a subsequent recognition test, older adults showed a larger reduction in associative than item memory, relative to young adults. For both age groups the number of eye gaze transitions between objects at encoding was correlated with associative recognition performance, suggesting that alternating attentional focus between items aids the generation of relational links necessary to encode associative memories. However, the relative time course of eye gaze transitions over the encoding interval for trials that were subsequently retrieved vs. forgotten differed between age groups. Furthermore, the ERPs of older adults exhibited strongly reduced frontal slow wave "subsequent memory effects", suggesting that they engaged to a lesser extent in working memory-based elaboration of the associative link. Based on these results, we propose that older adults exhibit a reduced tendency to generate and elaborate on internal representations of inter-item associative links. Rather, they use a less effective encoding strategy that disproportionally relies on the external stimulus display, resulting in lower associative memory performance.

Costs of storing colour and complex shape in visual working memory: Insights from pupil size and slow waves.

We investigated the impact of perceptual processing demands on visual working memory of coloured complex random polygons during change detection. Processing load was assessed by pupil size (Exp. 1) and additionally slow wave potentials (Exp. 2). Task difficulty was manipulated by presenting different set sizes (1, 2, 4 items) and by making different features (colour, shape, or both) task-relevant. Memory performance in the colour condition was better than in the shape and both condition which did not differ. Pupil dilation and the posterior N1 increased with set size independent of type of feature. In contrast, slow waves and a posterior P2 component showed set size effects but only if shape was task-relevant. In the colour condition slow waves did not vary with set size. We suggest that pupil size and N1 indicates different states of attentional effort corresponding to the number of presented items. In contrast, slow waves reflect processes related to encoding and maintenance strategies. The observation that their potentials vary with the type of feature (simple colour versus complex shape) indicates that perceptual complexity already influences encoding and storage and not only comparison of targets with memory entries at the moment of testing.

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.

Fast and careless or careful and slow? Apparent holistic processing in mental rotation is explained by speed-accuracy trade-offs.

A major debate in the mental-rotation literature concerns the question of whether objects are represented holistically during rotation. Effects of object complexity on rotational speed are considered strong evidence against such holistic representations. In Experiment 1, such an effect of object complexity was markedly present. A closer look on individual performance patterns, however, revealed that only some participants showed this effect. For others, rotational speed was independent of object complexity. The assumption that these fast-rotating participants use a holistic representation that equally well holds simple and complex objects would explain these results. Taking error rates into account disproved this explanation: Fast participants simply committed more errors in those conditions for which careful participants invested more rotation time. Whether this speed-accuracy trade-off is a stable personality trait or a somewhat flexible strategic choice was examined in Experiments 2 and 3. In Experiment 2, participants received monetary incentives that encouraged them to minimize errors. In line with a certain degree of flexible strategic control over speed-accuracy trade-offs, a large majority of participants showed effects of object complexity on rotational speed. When, in contrast, time pressure was induced in Experiment 3, error rates increased considerably and most participants' rotational speed became independent of object complexity. Our results indicate that all our participants performed mental rotation on a nonholistic representation and that apparent holistic processing strategies in mental rotation (and potentially also in other spatial tasks) might actually be speed-accuracy trade-offs in disguise.