Biology subjects

Sommer, W.

Publications and source records attributed to Sommer, W..

17 recordsLinked to original sources

bioRxiv2026

A Dual-Ensemble Model of Infralimbic Cortex Function in Behavioural Flexibility

The infralimbic cortex (IL) has been described as both facilitator and terminator of reward-seeking, yet both functions appear mutually exclusive. We reconcile this discrepancy by proposing a dual-ensemble model: one for action-outcome prediction and another for prediction correction. Using longitudinal miniscope imaging in rats, we show that during training, the action-outcome predictor ensemble sharpens its activity by suppressing the majority of the IL neuronal population. As contingencies stabilize, entropy decreases, reflecting a refined predictive model. During extinction, the prediction correction ensemble activates in response to reward omission. A computational simulation based on these two ensembles successfully recapitulated our experimental results. This framework reconciles conflicting models, where IL manipulation can either accelerate or abolish extinction by demonstrating that IL activity dynamically encodes predictive accuracy. Our findings indicate that IL functions as an action-outcome predictor that elegantly guides behavioural flexibility.

neuroscience↗

bioRxiv2025

Automatic Change Detection of Human Attractiveness: Comparing Visual and Auditory Perception

Change detection of social cues across individuals plays an important role in human interaction. Here we investigated the automatic change detection of facial and vocal attractiveness in 19 female participants by recording ERPs. We adopted a deviant-standard-reverse oddball paradigm where high- or low-attractive items were embedded as deviants in a sequence of opposite attractive standard stimuli. Both high- and low-attractive faces and voices elicited mismatch negativities (MMNs). Furthermore, low-attractive versus high-attractive items induced larger mismatch negativities in the voice condition but larger P3 amplitudes in the face condition. These data indicate that attractiveness can be automatically detected but that differences exist between facial and vocal attractiveness processing. Generally, change detection seems to work better for unattractive than attractive information possibly in line with a negativity bias.

neuroscience↗

bioRxiv2025

EEG-decodability of facial expressions and their stereoscopic depth cues in immersive virtual reality

Face perception typically occurs in three-dimensional space, where stereoscopic depth cues enrich the perception of facial features. Yet, most neurophysiological research on face processing relies on two-dimensional displays, potentially overlooking the role of stereoscopic depth information. Here, we combine immersive virtual reality (VR), electroencephalography (EEG), and eye tracking to examine the neural representation of faces under controlled manipulations of stereoscopic depth. Thirty-four participants viewed computer-generated faces with neutral, happy, angry, and surprised expressions in frontal view under monoscopic and stereoscopic viewing conditions. Using time-resolved multivariate decoding, we show that EEG signals in immersive VR conditions can reliably differentiate facial expressions. Stereoscopic depth cues elicited a distinct and decodable neural signature, confirming the sensitivity of our approach to depth-related processing. Yet, expression decoding remained robust across depth conditions, indicating that under controlled frontal viewing, the neural representation of behaviorally distinguishable facial expressions is invariant to binocular depth cues. Eye tracking showed that expression-related gaze patterns contained comparable information but did not account for neural representations, while depth information was absent in gaze patterns--consistent with dissociable representational processes. Our findings demonstrate the feasibility of EEG-based neural decoding in fully immersive VR as a tool for investigating face perception in naturalistic settings and provide new evidence for the stability of expression representations across depth variations in three-dimensional viewing conditions.

neuroscience↗

bioRxiv2023

Neural mechanism underlying preview effects and masked priming effects in visual word processing

Two classic experimental paradigms - masked repetition priming and the boundary paradigm - have played a pivotal role in understanding the process of visual word recognition. Traditionally, these paradigms have often been employed by different communities of researchers, with their own long-standing research traditions. Nevertheless, a review of the literature suggests that the brain-electric correlates of word processing established with both paradigms may show interesting similarities, in particular with regard to the location, timing, and direction of N1 and N250 effects. However, as of yet, no direct comparison has been undertaken between both paradigms. In the current study, we used combined eye-tracking/EEG to perform such a within-subject comparison using the same materials (single Chinese characters) as stimuli. Our results show the typical early repetition effects of N1 and N250 for both paradigms. However, repetition effects in N250 (i.e., a reduced negativity following identical-word primes/previews as compared to different-word primes/previews) were larger in the boundary paradigm than with masked priming. For N1 effects, repetition effects were similar across the two paradigms showing a larger N1 after repetitions as compared to alternations. Therefore, the results indicate that at the neural level, a briefly presented and masked foveal prime produces qualitatively similar facilitatory effects on visual word recognition as a parafoveal preview before a saccade, although such effects appear to be stronger in the latter case.

neuroscience↗

bioRxiv2023

Donor tissue-resident memory-like T and NK cells generate a transient peripheral chimerism in lung transplant recipients, potentially protective from chronic lung allograft dysfunction

Lung transplantation (LTx) is the only definite treatment option of patients suffering from end- stage lung disease. Long-term outcome is hampered by chronic allograft dysfunction resulting from poorly defined immune mechanisms. In this study of 97 lung recipients, we demonstrate dynamic changes of T, B and NK cell subsets early after lung transplantation with a selective decrease in memory CD4+ and CD8+ T cells accompanied by a relative increase in NK cells. Simultaneously, donor-derived T and NK cells were detected in recipient blood (n=44) immediately after LTx, persisting for three weeks. Donor T and NK cells displayed a CD69+ but CD103-CD49a- CD25- phenotype, which was shared by T and NK cells in lung perfusion solutions. In order to uncover the origin of these donor T and NK cells, the immune compartment of human lung explant tissue, i.e. trachea and parenchyma, was analyzed and it revealed three major subsets: classical circulating CD69-CD103-CD49a- T and NK cells, CD69+CD103+CD49a+ tissue-resident memory (TRM) T and NK cells and CD69+CD103-CD49a- TRM-like T and NK cells. Single-cell RNA sequencing confirmed the presence of TRM-like subsets with unique features, which reflected the phenotypes of donor T and NK cells and created a transient chimerism in recipient blood. Higher frequencies of donor T cells within the first three weeks showed a tendency for protection from chronic lung allograft dysfunction (CLAD) two years after transplantation although the correlation analyses did not reach statistical significance. To the best of our knowledge, we show for the first time that a transient chimerism is established within the first weeks after lung transplantation by donor TRM- like T and NK cells, which may contribute to protection from chronic lung allograft dysfunction (CLAD) development. Single Sentence SummaryDonor TRM-like T and NK cells cause a transient chimerism in lung recipients and potentially contribute to protection from CLAD.

immunology↗

bioRxiv2023

How the dominant reading direction changes parafoveal processing: A combined EEG/eye-tracking study

Reading directions vary across writing systems. Through long-term experience readers adjust their visual systems to the dominant reading direction in their writing systems. However, little is known about the neural correlates underlying these adjustments because different writing systems do not just differ in reading direction, but also regarding visual and linguistic properties. Here, we took advantage that Chinese is read to different degrees in left-right or top-down directions in different regions. We investigated visual word processing in participants from Taiwan (both top-down and left-right directions) and from mainland China (only left-right direction). Combined EEG/eye tracking was used together with a saccade-contingent parafoveal preview manipulation to investigate neural correlates, while participants read 5-word lists. Fixation-related potentials (FRPs) showed a reduced late N1 effect (preview positivity), but this effect was modulated by the prior experience with a specific reading direction. Results replicate previous findings that valid previews facilitate visual word processing, as indicated by reduced FRP activation. Critically, the results indicate that this facilitation effect depends on experience with a given reading direction, suggesting a specific mechanism how cultural experience shapes the way people process visual information.

neuroscience↗

bioRxiv2023

Visual short-term memory related EEG components in a virtual reality setup

Virtual reality (VR) offers a powerful tool for investigating cognitive processes, as it allows researchers to gauge behaviors and mental states in complex, yet highly controlled, scenarios. The use of VR head-mounted displays in combination with physiological measures such as EEG presents new challenges and raises the question whether established findings also generalize to a VR setup. Here, we used a VR headset to assess the spatial constraints underlying two well-established EEG correlates of visual short-term memory: the amplitude of the contralateral delay activity (CDA) and the lateralization of induced alpha power during memory retention. We tested observers visual memory in a delayed match-to-sample task with bilateral stimulus arrays of either two or four items while varying the horizontal eccentricity of the memory arrays (4, 9, or 14 degrees of visual angle). The CDA amplitude differed between high and low memory load at the two smaller eccentricities, but not at the largest eccentricity. Neither memory load nor eccentricity significantly influenced the observed alpha lateralization. We further fitted time-resolved spatial filters to decode memory load from the event-related potential as well as from its time-frequency decomposition. Classification performance during the retention interval was above chance level for both approaches and did not vary significantly across eccentricities. We conclude that commercial VR hardware can be utilized to study the CDA and lateralized alpha power, and we provide caveats for future studies targeting these EEG markers of visual memory in a VR setup. Impact statementCombining EEG with virtual reality, we studied how the eccentricity of a memory array during encoding affects well-known neural markers of visual short-term memory. We reveal that the previously reported occurrence of these EEG components during visual memory retention can be replicated in such a setup. These EEG markers were differently affected by eccentricity, hence providing valuable constraints for future experimental designs.

neuroscience↗

bioRxiv2022

Parafoveal and foveal N400 effects in natural sentence reading: Evidence from overlap-corrected fixation-related potentials

The depth at which parafoveal words are processed during reading is an ongoing topic of debate. Recent studies using RSVP-with-flanker paradigms have shown that implausible words within sentences elicit N400 components while they are still in parafoveal vision, suggesting that the semantics of parafoveal words can be accessed to rapidly update the sentence representation. To study this effect in natural reading, we combined the co-registration of eye movements and EEG with the deconvolution modeling of fixation-related potentials (FRPs) to test whether semantic plausibility is processed parafoveally during Chinese sentence reading. For one target word per sentence, both its parafoveal and foveal plausibility were orthogonally manipulated using the boundary paradigm. Consistent with previous eye movement studies, we observed a delayed effect of parafoveal plausibility on fixation durations that only emerged on the foveal word. Crucially, in FRPs aligned to the pre-target fixation, a clear N400 effect emerged already based on parafoveal plausibility, with more negative voltages for implausible previews. Once participants fixated the target, we again observed an N400 effect of foveal plausibility. Interestingly, this foveal N400 was absent whenever the preview had been implausible, indicating that when a words (im)plausibility is already processed in parafoveal vision, this information is not revised anymore upon direct fixation. Implausible words also elicited a late positive complex (LPC), but exclusively in foveal vision. Our results provide convergent neural and behavioral evidence for the parafoveal uptake of semantic information, but also indicate different contributions of parafoveal versus foveal information towards higher-level sentence processing.

neuroscience↗

bioRxiv2022

Auditory Language Comprehension During Saccadic Eye Movements: An Investigation Using the N400 Event-Related Brain Potential

In many situations of everyday life, it is important to quickly understand a spoken message despite distraction by an already ongoing activity. Previous dual-task studies recording the N400 component of the event-related potential (ERP) have shown that auditory language comprehension can be strongly delayed by temporally overlapping additional tasks. In the current study, we investigated whether this interference is aggravated by the need for saccadic eye movements and visuospatial attention shifts in the overlapping task. In two dual-task experiments, a synonymy judgment task for spoken words was combined with a visual discrimination task at different stimulus onset asynchronies. In half of the trials, the primary visual task required a 10{degrees} exogenous saccade towards a peripheral stimulus. The timing of semantic processing in the secondary task was assessed by recording the N400. We replicated that with increasing temporal overlap between the tasks, the N400 component was strongly delayed. However, additional saccade-related processes in the primary task had no detrimental effects on concurrent spoken language processing on their own. Unexpectedly, we also observed that a preceding saccade consistently facilitated subsequent motoric processing in the visual task (as indexed by manual reaction times and the lateralized readiness potential), suggesting that saccade execution as such can significantly enhance subsequent processing.

neuroscience↗

bioRxiv2021

Is there magnocellular facilitation of early neural processes underlying visual word recognition? Evidence from masked repetition priming with ERPs

An influential theory in the field of visual object recognition proposes that fast magnocellular (M) information facilitates neural processing of spatially more fine-grained but slower parvocellular (P) information. While written words can be considered as a special type of visual objects, it is unknown whether magnocellular facilitation also plays a role in reading. We used a masked priming paradigm that has been shown to result in neural facilitation in visual word processing and tested whether these facilitating effects are mediated by the magnocellular system. In two experiments, we manipulated the influence of magnocellular and parvocellular systems on visual processing of a contextually predictable target character by contrasting high versus low spatial frequency and luminance versus color contrast, respectively. In addition, unchanged (normal) primes were included in both experiments as a manipulation check. As expected, unchanged primes elicited typical repetition effects in the N1, N250 and P3 components of the ERP in both experiments. In the experiment manipulating spatial contrast, we obtained repetition effects only for the N1 component for both M- and P-biased primes. In the luminance versus color contrast experiment, repetition effects were found in N1 and N250 for both M- and P- biased primes. Furthermore, no interactions were found between M- vs. P-biased prime types and repetition. Together these results indicate that M- and P- information contributes jointly to early neural processes underlying visual word recognition.

neuroscience↗

bioRxiv2021

Parafoveal words can modulate sentence meaning: Electrophysiological evidence from an RSVP-with-flanker task

During natural reading, readers also take up some visual information from not-yet-fixated words to the right of the current fixation and it is well-established that this parafoveal preview facilitates the subsequent foveal processing of the word. However, the extraction and integration of word meaning from the parafoveal word and its possible influence on the semantic sentence context are controversial. In the current study, we recorded event-related potentials (ERPs) in the RSVP-with-flankers paradigm to test whether and how updates of sentential meaning that are based only on parafoveal information influence the subsequent foveal processing. Using Chinese sentences, the sentence congruency of parafoveal and foveal target words were orthogonally manipulated. In contrast to previous research, we also controlled for potentially confounding effects of parafoveal-to-foveal repetition priming (identity preview effects) on the N400. Crucially, we found that the classic effect of foveal congruency on the N400 component only appeared when the word in preview had been congruent with sentence meaning; in contrast, there was no N400 when the preview word had been incongruent. These results indicate that sentence meaning rapidly adapts to parafoveal preview, which already changes the context for the then fixated word. We also show that a correct parafoveal preview generally attenuates the N400 once a word is fixated, regardless of congruency. Taken together, our findings underline the highly generative and adaptive framework of language comprehension.

neuroscience↗

bioRxiv2021

Is there a G-factor in Hypnotic Suggestibility? Confirmatory Factor Analysis of the Harvard Group Scale of Hypnotic Suggestibility

Individuals differ in their responsiveness to hypnotic suggestions. However, defining and measuring hypnotizability is contentious because standardized scales, such as the Harvard group scale (HGSHS:A), measure a mixture of general suggestibility and its alteration due to hypnotic induction (hypnotizability). Exploratory factor analyses (FA) of standardized scales indicated their multidimensionality; however, the number and nature of latent factors are debated. We applied Confirmatory FA to the HGSHS:A scores of 477 volunteers and tested several theory-driven models. Scores were best explained by a bifactor model consisting of a G-factor and three correlated minor factors. The presented bifactor model shows that two sources of variability affect HGSHS:A simultaneously. Structural equation modeling revealed that the challenge-ideomotor factor predicts the other two minor factors, implying these suggestions might require more fundamental processes than other types. These results demonstrate the multifaceted and bifactorial structure of hypnotic suggestibility and underscore the desideratum for developing more differentiated scales.

neuroscience↗

bioRxiv2020

Resting state brain signal complexity of young healthy adults reflects genetic risk for developing Alzheimer Disease

The e4 allele of the APOE gene is strongly associated with impaired brain functionality and cognitive decline in humans at older age. It is controversial whether and how the APOE e4 allele is affecting brain activity among young healthy individuals and how such effects may contribute to individual differences in cognitive performance. Signal complexity is a critical aspect of brain activity that has been shown to be associated with brain function. In this study, we analyzed multiscale entropy (MSE) of EEG signals among young healthy adults as an indicator of brain signal complexity and investigated how MSE is predicted by APOE genotype groups. Furthermore, by means of structural equation modeling, we investigated whether MSE predicts fluid intelligence. Results indicate larger MSE in young healthy e4 carriers across all time scales. Moreover, better fluid intelligence (gf) is associated with smaller MSE at low time scales and larger MSE at higher scales. However, MSE does not account for better cognitive performance among APOE e4 carriers by mediating the APOE genotype effect on fluid intelligence. The present results shed further light on the neural mechanisms underlying gene-behavior association relevant for Alzheimers Disease risk.

neuroscience↗

bioRxiv2020

Time course and shared neurocognitive mechanisms of mental imagery and visual perception

When we imagine an object and when we actually see that object, similar brain regions become active. Yet, the time course and mechanisms with which imagery engages perceptual networks remain to be better understood. An emerging view holds that imagery and perception follow distinct dynamics during early visual processing with similarities arising only during later, high-level visual processing. However, confounds of visual stimulation and paradigms favoring observation of high-level processes associated with subjective imagery strength may have precluded evidence of earlier shared mechanisms. We therefore manipulated prior knowledge that informs early-stage top-down predictions and tracked electrophysiological brain responses while fully controlling visual stimulation. Participants saw and imagined objects associated with varying amounts of semantic knowledge. Imagery and perception were equally influenced by knowledge at an early stage (P1 component), revealing shared mechanisms that support low-level visual processing. This finding complements previous research by showing that imagery is not merely perception in reverse. Instead, in line with the predictive processing framework, both, perception and imagery are active and constructive processes that share top-down mechanisms already in early phases of processing.

neuroscience↗

bioRxiv2019

Eye contact in active and passive viewing: event-related brain potential evidence from a combined eye tracking and EEG study

Eye contact is a salient social cue which is assumed to influence early brain processes involved in face perception. The N170 component in the event-related potential (ERP) has frequently been reported to be larger to faces with an averted rather than direct gaze towards the observer. In most studies, however, this effect has been investigated in comparatively artificial, passive settings where participants were instructed to fixate their gaze while observing occasional gaze changes in stimulus faces. Yet, it is unclear whether similar mechanisms are in place during naturalistic gaze interactions involving the continuous interplay of directed and averted gaze between the communication partners. To fill this gap, we compared passive viewing of gaze change sequences with an active condition where participants own gaze continuously interacted with the gaze of a stimulus face; while recording ERPs and monitoring gaze with eye tracking. In addition, we investigated the relevance of emotional facial expressions for gaze processing. For both passive viewing and active interaction, N170 amplitudes were larger when the gaze of stimulus faces was averted rather than directed at the participants. Furthermore, eye contact decreased P300 amplitudes in both conditions. Emotional facial expression influenced N170 amplitudes but did not elicit an early posterior negativity nor did it interact with gaze direction. We conclude that comparable mechanisms of gaze perception are in place in gaze interaction as compared to passive viewing, encouraging the further study of the eye contact effect in naturalistic settings.

neuroscience↗

bioRxiv2018

I knew that! Confidence in outcome prediction and its impact on feedback processing and learning

Influential theories emphasize the importance of predictions in learning: we learn from feedback to the extent that it is surprising, and thus conveys new information. Here we explore the hypothesis that surprise depends not only on comparing current events to past experience, but also on online evaluation of performance via internal monitoring. Specifically, we propose that people leverage insights from response-based performance monitoring - outcome predictions and confidence - to control learning from feedback. In line with predictions from a Bayesian inference model, we find that people who are better at calibrating their confidence to the precision of their outcome predictions learn more quickly. Further in line with our proposal, EEG signatures of feedback processing are sensitive to the accuracy of, and confidence in, post-response outcome predictions. Taken together, our results suggest that online predictions and confidence serve to calibrate neural error signals to improve the efficiency of learning.

neuroscience↗

bioRxiv2018

Attentional modulation of orthographic neighborhood effects during reading: Evidence from event-related brain potentials in a psychological refractory period paradigm

It is often assumed that word reading proceeds automatically. Here, we tested this assumption by recording event-related potentials during a psychological refractory period (PRP) paradigm, requiring lexical decisions about written words. Specifically, we selected words differing in their orthographic neighborhood size - the number of words that can be obtained from a target by exchanging a single letter - and investigated how influences of this variable depend on the availability of central attention. As expected, when attentional resources for lexical decisions were unconstrained, words with many orthographic neighbors elicited larger N400 amplitudes than those with few neighbors. However, under conditions of high temporal overlap with a high priority primary task, the N400 effect disappeared. This finding indicates strong attentional influences on the incidental processing of orthographic neighbors during word reading, providing novel evidence against the automaticity of processes involved in word reading. Furthermore, in conjunction with the observation of an underadditive interaction between stimulus onset asynchrony (SOA) and orthographic neighborhood size in lexical decision performance, commonly taken to indicate automaticity, our results raise issues concerning the standard logic of cognitive slack in the PRP paradigm.

neuroscience↗