Real-time measurement of mental workload: A feasibility study

The primary goal of the study was to explore the utility of event-related brain potentials (ERP) as real-time measures of workload. To this end, subjects performed two different tasks both separately and together. One task required that subjects monitor a bank of constantly changing gauges and detect critical deviations. Difficulty was varied by changing the predictability of the gauges. The second task was mental arithmetic. Difficulty was varied by requiring subjects to perform operations on either two or three columns of numbers. Two conditions that could easily be distinguished on the basis of performance measures were selected for the real-time evaluation of ERPs. A bootstrapping approach was adopted in which one thousand samples of n trials (n = 1, 3, 5 ...65) were classified using several measures of P300 and Slow Wave amplitude. Classification accuracies of 85 percent were achieved with 25 trials. Results are discussed in terms of potential enhancements for real-time recording

Database of semantically associated and unassociated pairs of everyday objects for the study of memory in children : technical report

The present study aimed at creating a database of standardized pairs of semantically associated and unassociated everyday objects for the use in research in experimental developmental psychology. We had a large sample of 289 German school-aged children rate a set of 300 single objects, 150 semantically related, and 150 unrelated pairs. In a first step, the participants had to name the presented single objects to indicate the expe-rienced level of familiarity for each item. The second part of the study focused on the rating of association strength of the pairs of objects. Here, we used a three-point rating scale to have the participants decide on the magnitude of semantic relatedness. For each single object, a familiarity score and a naming agreement ratio were calculated to quan-tify the degree of the children\u27;s conceptual knowledge and familiarity with the selected objects. The relatedness scores computed for the pairs of objects can be used to divide the pairs into separate categories according to the strength semantic association. These rating procedures yielded a large and well controlled database of modern pictorial ma-terial for experimenters to choose from. It may be helpful for designing experiments in developmental psychology research with clinical and non-clinical populations

Mulitple ways to the prior occurrence of an event: An electrophysiological dissociation of experimental and conceptually driven familiarity

Contains fulltext : 221784.pdf (publisher's version ) (Closed access)Recent research has shown that familiarity contributes to associative memory when the to-be-associated stimuli are unitized during encoding. However, the specific processes underlying familiarity-based recognition of unitized representations are still indefinite. In this study, we present electrophysiologically dissociable early old/new effects, presumably related to two different kinds of familiarity inherent in associative recognition tasks. In a study-test associative recognition memory paradigm, we employed encoding conditions that established unitized representations of two pre-experimentally unrelated words, e.g. vegetable-bible. We compared event-related potentials (ERP) during the retrieval of these unitized word pairs using different retrieval cues. Word pairs presented in the same order as during unitization at encoding elicited a parietally distributed early old/new effect which we interpret as reflecting conceptually driven familiarity for newly formed concepts. Conversely, word pairs presented in reversed order only elicited a topographically dissociable early effect, i.e. the mid-frontal old/new effect, the putative correlate of experimental familiarity. The late parietal old/new effect, the putative ERP correlate of recollection, was obtained irrespective of word order, though it was larger for words presented in same order. These results indicate that familiarity may not be a unitary process and that different task demands can promote the assessment of conceptually driven familiarity for novel unitized concepts or experimentally-induced increments of experimental familiarity, respectively.13 p

Improving episodic memory: frontal-midline theta neurofeedback training increases source memory performance

Cognitive and neurofeedback training (NFT) studies have demonstrated that training-induced alterations of frontal-midline (FM) theta activity (4-8 Hz) transfer to cognitive control processes. Given that FM theta oscillations are assumed to provide top-down control for episodic memory retrieval, especially for source retrieval, that is, accurate recollection of contextual details of prior episodes, the present study investigated whether FM theta NFT transfers to memory control processes. It was assessed (1) whether FM theta NFT improves source retrieval and modulates its underlying EEG characteristics and (2) whether this transfer extends over two posttests. Over seven NFT sessions, thetraining group who trained individual FM theta activity showed greater FM theta increase than an active control group who trained randomly chosen frequency bands. The training group showed better source retrieval in a posttraining session performed 13 days after NFT and their performance increasesfrom pre- to both posttraining sessions were predicted by NFT theta increases. Thus, training-induced enhancement of memory control processes seems to protect newly formed memories from proactive interference of previously learned information. EEG analyses revealed that during pretest both groups showed source memory specific theta activity at frontal and parietal sites. Surprisingly, training-induced improvements in source retrieval tended to be accompanied by less prestimulus FM theta activity, which was predicted by NFT theta change for the training but not the control group, suggesting a more efficient use of memory control processes after training. The present findings provide unique evidence for the enhancement of memory control processes by FM theta NFT

Task context dissociates the FN400 and the N400

In event-related potential studies, familiarity-based recognition has been associated with the FN400, that is, more positive-going waveforms for old items than new items 300–500ms post-stimulus onset, maximal at frontal electrodes. We tested the proposition that the FN400 reflects the attribution of unexpected processing fluency to familiarity. This implies that the FN400 is greater when fluency is less expected, that is, for less familiar stimuli. Moreover, the FN400 should be modulated by the goal of remembering and only elicited when fluency is correctly attributed to the past, that is, by correct old responses in recognition memory tests. In the absence of a retrieval task, enhanced fluency for repeated items should be associated with an N400 attenuation as no episodic attribution takes place. In an incidental study-test design with words of low and high lifetime familiarity, participants made pleasantness judgments for half of the studied words. The other half re-appeared in a recognition test. Only in the latter task, participants had the goal of remembering. As both tasks included also new words, we could compare old/new effects under conditions in which both effects are driven by increased fluency for repeated words. We did not find the expected differences in the FN400 for low vs. high life-time familiarity items. However, as expected, we found a frontally distributed FN400 in the recognition test whereas the old/new effect in the pleasantness task resembled an N400 effect. This supports the view that the FN400 occurs when fluency is attributed to familiarity during a recognition decision

Improving cognitive control: Is theta neurofeedback training associated with proactive rather than reactive control enhancement?

Frontal-midline (FM) theta activity (4–8 Hz) is proposed to reflect a mechanism for cognitive control that is needed for working memory retention, manipulation, and interference resolution. Modulation of FM theta activity via neurofeedback training (NFT) demonstrated transfer to some but not all types of cognitive control. Therefore, the present study investigated whether FM theta NFT enhances performance and modulates underlying EEG characteristics in a delayed match to sample (DMTS) task requiring mainly proactive control and a color Stroop task requiring mainly reactive control. Moreover, temporal characteristics of transfer were explored over two posttests. Across seven 30-min NFT sessions, an FM theta training group exhibited a larger FM theta increase compared to an active control group who upregulated randomly chosen frequency bands. In a posttest performed 13 days after the last training session, the training group showed better retention performance in the DMTS task. Furthermore, manipulation performance was associated with NFT theta increase for the training but not the control group. Contrarily, behavioral group differences and their relation to FM theta change were not significant in the Stroop task, suggesting that NFT is associated with proactive but not reactive control enhancement. Transfer to both tasks at a posttest one day after training was not significant. Behavioral improvements were not accompanied by changes in FM theta activity, indicating no training-induced modulation of EEG characteristics. Together, these findings suggest that NFT supports transfer to cognitive control that manifests late after training but that other training-unspecific factors may also contribute to performance enhancement

Intra- and Inter-Item Associations Doubly Dissociate the Electrophysiological Correlates of Familiarity and Recollection

SummarySingle-process models of recognition memory posit that recognizing is based on a unidimensional value of global memory strength. By contrast, dual-process models propose the existence of two independent processes subserving the explicit recognition of previously encountered episodes, namely “familiarity” and “recollection.” Familiarity represents a noncontextual form of recognition that may only support the retrieval of associative information when the to-be-associated information can be unitized, such as when two photographs depicting the same person are memorized (intra-item associations). Conversely, recollection enables retrieving associations between arbitrarily linked information, such as associations between photographs of different persons (inter-item associations). By measuring event-related brain potentials (ERPs), we obtained a double dissociation of familiarity and recollection that strongly favors dual-process accounts of recognition memory: the electrophysiological correlate of familiarity was significantly larger for intra- than for inter-item associations. Conversely, the electrophysiological correlate of recollection was significantly larger for inter- than for intra-item associations

Picture database of morphed faces (MoFa) : technical report

In the present study, a morphing and picture processing procedure was used to create a database of 100 face-pairs, which were morphed into one another in steps of 5%. Furthermore, 240 face stimuli were also included that were not morphed but may be used for control purposes. The face stimuli chosen for this database were with minimal or neutral emotional facial expression. In two experiments, selected items of the face stimuli were rated by participants in order to reveal (a) the minimal degree to which a face can be morphed such that a physical change but no identity change is apparent and (b) the degree to which a face needs to be morphed such that the morphed face is perceived as representing a different person than the initial face. The results show that 35% morphed faces mainly seem to fulfill condition (a) while 70% morphed faces mainly fulfill condition (b), especially when outlying morph-pairs are excluded. In conclusion, the present database provides morphed stimulus material that was rated by a moderately large number of participants and may be used for broad experimental purposes

Effects of emotional study context on immediate and delayed recognition memory: Evidence from event-related potentials

Whilst research has largely focused on the recognition of emotional items, emotion may be a more subtle part of our surroundings and conveyed by context rather than by items. Using ERPs, we investigated which effects an arousing context during encoding may have for item-context binding and subsequent familiarity-based and recollection-based item-memory. It has been suggested that arousal could facilitate item-context bindings and by this enhance the contribution of recollection to subsequent memory judgements. Alternatively, arousal could shift attention onto central features of a scene and by this foster unitisation during encoding. This could boost the contribution of familiarity to remembering. Participants learnt neutral objects paired with ecologically highly valid emotional faces whose names later served as neutral cues during an immediate and delayed test phase. Participants identified objects faster when they had originally been studied together with emotional context faces. Items with both neutral and emotional context elicited an early frontal ERP old/new difference (200-400 ms). Neither the neurophysiological correlate for familiarity nor recollection were specific to emotionality. For the ERP correlate of recollection, we found an interaction between stimulus type and day, suggesting that this measure decreased to a larger extend on Day 2 compared with Day 1. However, we did not find direct evidence for delayed forgetting of items encoded in emotional contexts at Day 2. Emotion at encoding might make retrieval of items with emotional context more readily accessible, but we found no significant evidence that emotional context either facilitated familiarity-based or recollection-based item-memory after a delay of 24 h