Electrophysiological Correlates of the Interaction of Physical and Numerical Size in Symbolic Number Processing: Insights from a Novel Go/Nogo Numerical Stroop Task.

The interaction of physical and numerical size has been investigated and repeatedly demonstrated in the numerical Stroop task, in which participants compare digits of different physical sizes. It is, however, not entirely clear yet what psychological processes contribute to this interaction. The aim of the present study is to investigate the role of inhibition in the interaction of physical and numerical size, by introducing a novel paradigm that is suitable to elicit inhibition-related event-related potential components. To this end, we combined the go/nogo paradigm with the numerical Stroop task while measuring EEG and reaction times. Participants were presented with Arabic number pairs and had to press a button if the number on one side was numerically larger and they had to refrain from responding if the number on the other side was numerically larger. The physical size of the number pairs was also manipulated, in order to create congruent, neutral, and incongruent trials. Behavioural results confirmed the well-established numerical distance and numerical Stroop effects. Analysis of electrophysiological data revealed the classical go/nogo electrophysiological effects with numerical stimuli, and showed that peak amplitudes were larger for nogo than for go trials on the N2, as well as on the P3 component, on frontal and midline electrodes. When analysing the congruency effects, the peak amplitude of N2 was larger in incongruent trials than in neutral and congruent trials, while there was no evidence of a congruency effect on the P3 component peaks. Further analysis of the electrophysiological data revealed an additional facilitatory effect in the go trials, as well as an additional interference effect in the nogo trials. Taken together, it seems that interference effects are probably resolved by inhibitory processes and that facilitatory effects are affected by different cognitive control processes required by go versus nogo trials.

Attentional bias in German Armed Forces veterans with and without posttraumatic stress symptoms - An eye-tracking investigation and group comparison.

BACKGROUND AND OBJECTIVES: Most eye tracking based paradigms evidence patterns of sustained attention on threat coupled with low evidence for vigilance to or avoidance of threat in posttraumatic stress symptoms (PTSS). Still, eye tracking data on attention bias is particularly limited for military population. This eye tracking study investigated attentional bias in PTSS in a sample of German Armed Forces veterans. METHODS: Veterans with deployment-related PTSS (N = 24), veterans with deployment-related traumatization without PTSS (N = 28), and never-deployed healthy veterans (N = 18) were presented with pairs of combat and neutral pictures, pairs of general threat and neutral pictures, and pairs of emotional and neutral faces. Their eye gazes were tracked during a free viewing task. 3 x 3 x 2 mixed general linear model analyses were conducted. Internal consistency of attention bias indicators was calculated for the entire sample and within groups. RESULTS: Veterans with PTSS dwelled longer on general threat AOIs in contrast to non-exposed controls and shorter on general threat and combat associated neutral AOIs in contrast to both control groups. Veterans with PTSS entered faster to general threat AOIs than non-exposed controls. Veterans with PTSS showed circumscribed higher attention fluctuation in contrast to controls. Internal consistency varied across attention bias indicators. LIMITATIONS: Statistical power was reduced due to recruitment difficulties. CONCLUSIONS: Evidence is provided for the maintenance hypothesis in PTSS. No robust evidence is provided for hypervigilant behavior in PTSS. Findings on attention bias variability remain unclear, calling for more investigations in this field.

Feigning memory impairment in a forced-choice task: Evidence from event-related potentials.

Strategies of malingering detection have brought about a wealth of neuropsychological studies in the last decades. However, the investigation of physiological measures to reliably differentiate between authentic and manipulated symptom presentations is still in its infancy. The present study examined event-related potentials (ERP) to identify feigned memory impairment. We tested instructed malingerers (n = 25) and control participants (n = 22) with a recognition task similar to the Test of Memory Malingering. No differences between groups were found for P1 (70-110 ms) but for N1 (120-170 ms) and P300 components, with lower amplitudes for instructed malingerers. Behavioral data showed a typical pattern of unrealistically high errors in a forced-choice recognition task and less overall recalled stimuli in instructed malingerers. We also found study-phase repetition and old/new effects in the P300, but no interactions with groups (control vs. malingering). Post-hoc analyses revealed that the P300 effect is greater when participants reported an attention-based faking strategy, as opposed to response-based malingerers and controls. The employment of physiological measures can yield additional information on the validity of test data without the need to perform additional tests.

Effects of transcranial direct current stimulation on the cognitive control of negative stimuli in borderline personality disorder.

Borderline personality disorder (BPD) is characterized by impairments in the cognitive control of negative information. These impairments in cognitive control are presumably due to blunted activity of the dorsolateral prefrontal cortex (dlPFC) along with enhanced activations of the limbic system. However, the impact of an excitatory stimulation of the dlPFC still needs to be elucidated. In the present study, we therefore assigned 50 patients with BPD and 50 healthy controls to receive either anodal or sham stimulation of the right dlPFC in a double-blind, randomized, between-subjects design. Participants performed a delayed working memory task with a distracter period during which a grey background screen, or neutral, or negative stimuli were presented. This experimental paradigm was first evaluated in a pilot study with 18 patients with BPD and 19 healthy controls. In both studies, patients with BPD showed an impairment of cognitive control when negative distracters were presented in the delay period of a working memory task. However, excitatory stimulation of the right dlPFC did not ameliorate cognitive control of negative stimuli in BPD, which raises questions about the specific role of the right dlPFC for the understanding of BPD psychopathology. Methodological limitations are discussed.

Brain stimulation during an afternoon nap boosts slow oscillatory activity and memory consolidation in older adults.

Sleep-related consolidation of declarative memories, as well as associated neurophysiological events such as slow oscillatory and spindle activity, deteriorate in the course of aging. This process is accelerated in neurodegenerative disease. Transcranial slow oscillatory stimulation (so-tDCS) during sleep has been shown to enhance slow oscillatory brain activity and thereby improve memory consolidation in young subjects. Here, we investigated whether so-tDCS applied to older adults during an afternoon nap exerts similar effects. Eighteen older human subjects were assessed using visuo-spatial (picture memory, primary, and location memory) and verbal memory tasks before and after a 90-min nap either comprising weak so-tDCS at 0.75Hz over fronto-central location or sham (no) stimulation in a within-subject design. Electroencephalographic activity was recorded throughout the naps and immediate effects of stimulation on brain activity were evaluated. Here, spectral power within three frequency bands of interest were computed, i.e., slow oscillatory activity, slow spindle and fast spindle activity; in 1-min stimulation-free intervals following 5 stimulation blocks. So-tDCS significantly increased frontal slow oscillatory activity as well as fast spindle activity, and significantly improved picture memory retention after sleep. Retention in the location memory subtask and in the verbal memory task was not affected. These findings may indicate a novel strategy to counteract cognitive decline in aging in a convenient manner during brief daytime naps.

Boosting Slow Oscillatory Activity Using tDCS during Early Nocturnal Slow Wave Sleep Does Not Improve Memory Consolidation in Healthy Older Adults.

BACKGROUND: Previous studies have demonstrated an enhancement of hippocampal-dependent declarative memory consolidation, associated slow wave sleep (SWS) and slow wave activity (SWA) after weak slow oscillatory stimulation (so-tDCS) during early non-rapid eye movement sleep (NREM) in young adults. Recent studies in older individuals could not confirm these findings. However, it remained unclear if this difference was due to variations in study protocol or to the age group under study. OBJECTIVE/HYPOTHESIS: Here, we asked if so-tDCS promotes neurophysiological events and associated sleep-dependent memory in the visuo-spatial domain in older adults, using a stimulation protocol that closely resembled the one employed in young adults. METHODS: In a randomized, placebo-controlled single-blind (participant) crossover study so-tDCS (0.75 Hz; max. current density 0.522 mA/cm(2)) vs. sham stimulation was applied over the frontal cortex of 21 healthy older subjects. Impact of stimulation on frequency band activity (linear mixed models), two declarative and one procedural memory tasks (repeated measures ANOVA) and percentage of sleep stages (comparison of means) was assessed. RESULTS: so-tDCS, as compared to sham, increased SWA and spindle activity immediately following stimulation, accompanied by significantly impaired visuo-spatial memory consolidation. Furthermore, verbal and procedural memory remained unchanged, while percentage of NREM sleep stage 4 was decreased over the entire night (uncorrected). CONCLUSION: so-tDCS increased SWA and spindle activity in older adults, events previously associated with stimulation-induced improved consolidation of declarative memories in young subjects. However, consolidation of visuo-spatial (primary outcome) and verbal memories was not beneficially modulated, possibly due to decline in SWS over the entire night that may have prevented and even reversed immediate beneficial effects of so-tDCS on SWA.

An electrophysiological investigation of non-symbolic magnitude processing: numerical distance effects in children with and without mathematical learning disabilities.

INTRODUCTION: The aim of the present study was to probe electrophysiological effects of non-symbolic numerical processing in 20 children with mathematical learning disabilities (mean age = 99.2 months) compared to a group of 20 typically developing matched controls (mean age = 98.4 months). METHODS: EEG data were obtained while children were tested with a standard non-symbolic numerical comparison paradigm that allowed us to investigate the effects of numerical distance manipulations for different set sizes, i.e., the classical subitizing, counting and estimation ranges. Effects of numerical distance manipulations on event-related potential (ERP) amplitudes as well as activation patterns of underlying current sources were analyzed. RESULTS: In typically developing children, the amplitudes of a late parietal positive-going ERP component showed systematic numerical distance effects that did not depend on set size. For the group of children with mathematical learning disabilities, ERP distance effects were found only for stimuli within the subitizing range. Current source density analysis of distance-related group effects suggested that areas in right inferior parietal regions are involved in the generation of the parietal ERP amplitude differences. CONCLUSION: Our results suggest that right inferior parietal regions are recruited differentially by controls compared to children with mathematical learning disabilities in response to non-symbolic numerical magnitude processing tasks, but only for stimuli with set sizes that exceed the subitizing range.

Remembering words in context as predicted by an associative read-out model.

Interactive activation models (IAMs) simulate orthographic and phonological processes in implicit memory tasks, but they neither account for associative relations between words nor explicit memory performance. To overcome both limitations, we introduce the associative read-out model (AROM), an IAM extended by an associative layer implementing long-term associations between words. According to Hebbian learning, two words were defined as "associated" if they co-occurred significantly often in the sentences of a large corpus. In a study-test task, a greater amount of associated items in the stimulus set increased the "yes" response rates of non-learned and learned words. To model test-phase performance, the associative layer is initialized with greater activation for learned than for non-learned items. Because IAMs scale inhibitory activation changes by the initial activation, learned items gain a greater signal variability than non-learned items, irrespective of the choice of the free parameters. This explains why the slope of the z-transformed receiver-operating characteristics (z-ROCs) is lower one during recognition memory. When fitting the model to the empirical z-ROCs, it likewise predicted which word is recognized with which probability at the item-level. Since many of the strongest associates reflect semantic relations to the presented word (e.g., synonymy), the AROM merges form-based aspects of meaning representation with meaning relations between words.

Electrophysiological correlates of non-symbolic numerical magnitude processing in children: joining the dots.

Whether and in what way enumeration processes differ for small and large sets of objects is still a matter of debate. In order to shed light on this issue, EEG data were obtained from 60 normally developing elementary school children. Adopting a standard non-symbolic numerical comparison paradigm allowed us to manipulate numerical distance between stimulus arrays for different quantity ranges, i.e. the subitizing, counting and estimation ranges. In line with the existing literature, the amplitudes of parietal positive going ERP components showed systematic effects of numerical distance, which did not depend on set size. In contrast to the similarities in surface distribution of electrophysiological activity across all number ranges, applying source localization we found distance related current density effects in inferior parietal processing systems to be similar for all numerical ranges, there was, however, considerable variation in the involvement of medial parietal and lateral occipital regions. The precuneus, which is known to be involved in visual imagery, showed distance effects exclusively for numerical comparisons on large set sizes. In contrast, the processing of small quantities and stimulus arrays arranged into canonical patterns relied on lateral occipital areas that are linked to higher-level shape recognition. These findings suggest, on the one hand, that for explicit numerical decisions an involvement of domain-specific resources does not depend on quantity features of the visual input. On the other hand, it seems that the recruitment of mediating perceptual systems differs between the apprehension of small quantities and the enumeration of large sets of objects.

Human striatal activation during adjustment of the response criterion in visual word recognition.

Results of recent computational modelling studies suggest that a general function of the striatum in human cognition is related to shifting decision criteria in selection processes. We used functional magnetic resonance imaging (fMRI) in 21 healthy subjects to examine the hemodynamic responses when subjects shift their response criterion on a trial-by-trial basis in the lexical decision paradigm. Trial-by-trial criterion setting is obtained when subjects respond faster in trials following a word trial than in trials following nonword trials - irrespective of the lexicality of the current trial. Since selection demands are equally high in the current trials, we expected to observe neural activations that are related to response criterion shifting. The behavioural data show sequential effects with faster responses in trials following word trials compared to trials following nonword trials, suggesting that subjects shifted their response criterion on a trial-by-trial basis. The neural responses revealed a signal increase in the striatum only in trials following word trials. This striatal activation is therefore likely to be related to response criterion setting. It demonstrates a role of the striatum in shifting decision criteria in visual word recognition, which cannot be attributed to pure error-related processing or the selection of a preferred response.

The numerical stroop effect in primary school children: a comparison of low, normal, and high achievers.

Sixty-six primary school children were selected, of which 21 scored low on a standardized math achievement test, 23 were normal, and 22 high achievers. In a numerical Stroop experiment, children were asked to make numerical and physical size comparisons on digit pairs. The effects of congruity and numerical distance were determined. All children exhibited congruity and distance effects in the numerical comparison. In the physical comparison, children of all performance groups showed Stroop effects when the numerical distance between the digits was large but failed to show them when the distance was small. Numerical distance effects depended on the congruity condition, with a typical effect of distance in the congruent, and a reversed distance effect in the incongruent condition. Our results are hard to reconcile with theories that suggest that deficits in the automaticity of numerical processing can be related to differential math achievement levels. Immaturity in the precision of mappings between numbers and their numerical magnitudes might be better suited to explain the Stroop effects in children. However, as the results for the high achievers demonstrate, in addition to numerical processing capacity per se, domain-general functions might play a crucial role in Stroop performance, too.

Affective processing within 1/10th of a second: High arousal is necessary for early facilitative processing of negative but not positive words.

Lexical decisions to high- and low-arousal negative words and to low-arousal neutral and positive words were examined in an event-related potentials (ERP) study. Reaction times to positive and high-arousal negative words were shorter than those to neutral (low-arousal) words, whereas those to low-arousal negative words were longer. A similar pattern was observed in an early time window of the ERP response: Both positive and high-arousal negative words elicited greater negative potentials in a time frame of 80 to 120 msec after stimulus onset. This result suggests that arousal has a differential impact on early lexical processing of positive and negative words. Source localization in the relevant time frame revealed that the arousal effect in negative words is likely to be localized in a left occipito-temporal region including the middle temporal and fusiform gyri. The ERP arousal effect appears to result from early lexico-semantic processing in high-arousal negative words.

Syllables and bigrams: orthographic redundancy and syllabic units affect visual word recognition at different processing levels.

Over the last decade, there has been increasing evidence for syllabic processing during visual word recognition. If syllabic effects prove to be independent from orthographic redundancy, this would seriously challenge the ability of current computational models to account for the processing of polysyllabic words. Three experiments are presented to disentangle effects of the frequency of syllabic units and orthographic segments in lexical decision. In Experiment 1 the authors obtained an inhibitory syllable frequency effect that was unaffected by the presence or absence of a bigram trough at the syllable boundary. In Experiments 2 and 3 an inhibitory effect of initial syllable frequency but a facilitative effect of initial bigram frequency emerged when manipulating 1 of the 2 measures and controlling for the other in Spanish words starting with consonant-vowel syllables. The authors conclude that effects of syllable frequency and letter-cluster frequency are independent and arise at different processing levels of visual word recognition. Results are discussed within the framework of an interactive activation model of visual word recognition.

The pseudohomophone effect: evidence for an orthography-phonology-conflict.

The standard pseudohomophone effect in the lexical decision task, i.e. longer response times and higher error rates for pseudohomophones compared with spelling controls, is commonly explained by an orthography-phonology-conflict. This study tested this conflict account, using a multi-method approach including participant's behavioral responses, confidence ratings, pupillary responses and event-related potentials (ERPs). The classic pseudohomophone effect was replicated using relatively long, multi-syllabic stimuli. Pseudohomophones were rated less confidently as being nonwords than spelling controls, and they affected the pupillary response by increasing the peak pupil diameter. Both findings are interpreted in terms of increased conflict and higher cognitive demands leading to uncertainty while solving the task. The ERP revealed an N400 component for spelling controls, showing a graded effect: word

Does familiarity or conflict account for performance in the word-stem completion task? Evidence from behavioural and event-related-potential data.

The conflict monitoring theory (CMT) assumes that word-stems associated with several completions should lead to crosstalk and conflict due to underdetermined responding situation (Botvinick et al. in Psychol Rev 108(3):624-652, 2001). In contrast, the Multiple-Read-Out-Model (MROM) of Jacobs and Grainger (J Exp Psychol 20(6): 1311-1334, 1994) predicts a high level of general lexical activity (GLA) for word-stems with many completions, indicating a higher stimulus familiarity because these stems are more probable to be read. We compared word-stems with several completions against word-stems with one possible completion while measuring response times and electrophysiological recordings. Slowest response times and a distinct FN400 component, which has previously been related to the concept of familiarity (Curran in Memory Cogn 28(6):923-938, 2000), were apparent for word-stems that could only be associated with a single response. These findings support the claims of the MROM. Furthermore, the lack of the N2-component for word-stems with several completions continues to challenge the EEG-extension of the CMT (Yeung et al. in Psychol Rev 111(4):2004).

Conflict monitoring engages the mediofrontal cortex during nonword processing.

The current study investigated the role played by conflict monitoring in a lexical-decision task involving competing word representations, using event-related potentials. We extended the multiple read-out model (Grainger and Jacobs, 1996), a connectionist model of word recognition, to quantify conflict by means of Hopfield Energy, which is defined as the sum of the products of all orthographic word node pair activations within the artificial mental lexicon of this model. With increasing conflict levels in nonwords, a late negativity increased in amplitude (400-600 ms) accompanied by activation of the anterior cingulate cortex and the medial frontal gyrus. The simulated conflict predicted the amplitudes associated with this mediofrontal conflict-monitoring network on an item level, and is consistent with the conflict-monitoring theory.

Event-related theta activity reflects memory processes in pronoun resolution.

A recent eye-tracking study reported a reverse effect of a noun's lexical frequency in the context of the resolution of coreferring pronouns. Investigating the neurophysiological basis of this effect, the present electroencephalographic study found differential patterns in theta activation when participants read pronouns referring to nouns of different frequency classes. Evoked theta power after pronoun onset increased with the frequency of the critical noun. This finding suggests differential load on memory resources depending on the nouns' frequency. Elevated attention promoting memory encoding for low-frequency words is assumed to facilitate the resolution of pronouns. Location of sources of differential theta activity in the parahippocampal region is accounted for by its role in an association network that mediates memory processes.

Does the frequency of the antecedent noun affect the resolution of pronominal anaphors? An ERP study.

Behavioral studies investigating the influence of the relative word frequency of antecedent nouns on the processing of anaphoric pronouns have yielded contradictory results. While some researchers found no effect of an antecedent's frequency of occurrence on coreference resolution [J. Simner, R. Smyth, Phonological activation in anaphoric lexical access (ALA), Brain Lang. 68 (1999) 40-45], others report shorter reading times for pronouns referring to low compared to high frequency nouns [R.G.P. van Gompel, A. Majid, Antecedent frequency effects during the processing of pronouns, Cognition 90 (2004) 255-264]. Using event-related potentials, our study aimed to further investigate the issue. Participants were presented with sentence pairs, of which the first contained either a high frequency, a middle frequency or a low frequency noun. The second sentence contained a pronoun which referred back to the noun in the first sentence. ERP waves were determined, time-locked to both the nouns and the anaphoric pronouns. We observed a graded N400 effect for antecedents of the three frequency classes with amplitudes reversely related to the word's lexical frequency. Coreferential pronouns elicited a P300, with amplitudes dependent on the noun's relative frequency of occurrence, i.e. the lower the antecedent's word frequency, the higher was the amplitude of the P300. This amplitude effect at the pronoun is interpreted in terms of the allocation of attentional resources to salient discourse entities.