Search

Conventionally, event-related potential (ERP) analysis relies on the researcher to identify the sensors and time points where an effect is expected. However, this approach is prone to bias and may limit the ability to detect unexpected effects or to investigate the full range of the electroencephalography (EEG) signal. Data-driven approaches circumvent this limitation, however, the multiple comparison problem and the statistical correction thereof affect both the sensitivity and specificity of the analysis. In this study, we present SHERPA – a novel approach based on explainable artificial intelligence (XAI) designed to provide the researcher with a straightforward and objective method to find relevant latency ranges and electrodes. SHERPA is comprised of a convolutional neural network (CNN) for classifying the conditions of the experiment and SHapley Additive exPlanations (SHAP) as a post hoc explainer to identify the important temporal and spatial features. A classical EEG face perception experiment is employed to validate the approach by comparing it to the established researcher- and data-driven approaches. Likewise, SHERPA identified an occipital cluster close to the temporal coordinates for the N170 effect expected. Most importantly, SHERPA allows quantifying the relevance of an ERP for a psychological mechanism by calculating an "importance score". Hence, SHERPA suggests the presence of a negative selection process at the early and later stages of processing. In conclusion, our new method not only offers an analysis approach suitable in situations with limited prior knowledge of the effect in question but also an increased sensitivity capable of distinguishing neural processes with high precision. [ABSTRACT FROM AUTHOR]

In the human electroencephalogram (EEG), induced oscillatory responses in various frequency bands are regarded as valuable indices to examine the neural mechanisms underlying human memory. While the advent of virtual reality (VR) drives the investigation of mnemonic processing under more lifelike settings, the joint application of VR and EEG methods is still in its infancy (e.g., due to technical limitations impeding the signal acquisition). The objective of the present EEG study was twofold. First, we examined whether the investigation of induced oscillations under VR conditions yields equivalent results compared to standard paradigms. Second, we aimed at obtaining further insights into basic memory-related brain mechanisms in VR. To these ends, we relied on a standard implicit memory design, namely repetition priming, for which the to-be-expected effects are well-documented for conventional studies. Congruently, we replicated a suppression of the evoked potential after stimulus onset. Regarding the induced responses, we observed a modulation of induced alphaband in response to a repeated stimulus. Importantly, our results revealed a repetition-related suppression of the high-frequency induced gammaband response (>30 Hz), indicating the sharpening of a cortical object representation fostering behavioral priming effects. Noteworthy, the analysis of the induced gammaband responses required a number of measures to minimize the influence of external and internal sources of artefacts (i.e., the electrical shielding of the technical equipment and the control for miniature eye movements). In conclusion, joint VR–EEG studies with a particular focus on induced oscillatory responses offer a promising advanced understanding of mnemonic processing under lifelike conditions. [ABSTRACT FROM AUTHOR]

The perception of faces is one of the most specialized visual processes in the human brain and has been investigated by means of the early event-related potential component N170. However, face perception has mostly been studied in the conventional laboratory, i.e., monitor setups, offering rather distal presentation of faces as planar 2D-images. Increasing spatial proximity through Virtual Reality (VR) allows to present 3D, real-life-sized persons at personal distance to participants, thus creating a feeling of social involvement and adding a self-relevant value to the presented faces. The present study compared the perception of persons under conventional laboratory conditions (PC) with realistic conditions in VR. Paralleling standard designs, pictures of unknown persons and standard control images were presented in a PC- and a VR-modality. To investigate how the mechanisms of face perception differ under realistic conditions from those under conventional laboratory conditions, the typical face-specific N170 and subsequent components were analyzed in both modalities. Consistent with previous laboratory research, the N170 lost discriminatory power when translated to realistic conditions, as it only discriminated faces and controls under laboratory conditions. Most interestingly, analysis of the later component [230-420 ms] revealed more differentiated face-specific processing in VR, as indicated by distinctive, stimulus-specific topographies. Complemented by source analysis, the results on later latencies show that face-specific neural mechanisms are applied only under realistic conditions [ABSTRACT FROM AUTHOR]

Sleep promotes the consolidation of newly acquired associative memories. Here we used neuronal oscillations in the human EEG to investigate sleep-dependent changes in the cortical memory trace. The retrieval activity for object-color associations was assessed immediately after encoding and after 3 hr of sleep or wakefulness. Sleep had beneficial effects on memory performance and led to reduced event-related theta and gamma power during the retrieval of associative memories. Furthermore, eventrelated alpha suppression was attenuated in the wake group for memorized and novel stimuli. There were no sleep-dependent changes in retrieval activity for missed items or items retrieved without color. Thus, the sleep-dependent reduction in theta and gamma oscillations was specific for the retrieval of associative memories. In line with theoretical accounts on sleep-dependent memory consolidation, decreased theta may indicate reduced mediotemporal activity because of a transfer of information into neocortical networks during sleep, whereas reduced parietal gamma may reflect effects of synaptic downscaling. Changes in alpha suppression in the wake group possibly index reduced attentional resources that may also contribute to a lower memory performance in this group. These findings indicate that the consolidation of associative memories during sleep is associated with profound changes in the cortical memory trace and relies on multiple neuronal processes working in concert. [ABSTRACT FROM AUTHOR]

In cognitive neuroscience, interest in the neuronal basis underlying the processing of human bodies is steadily increasing. Based on functional magnetic resonance imaging studies, it is assumed that the processing of pictures of human bodies is anchored in a network of specialized brain areas comprising the extrastriate and the fusiform body area (EBA, FBA). An alternative to examine the dynamics within these networks is electroencephalography, more specifically so-called steady-state visually evoked potentials (SSVEPs). In SSVEP tasks, a visual stimulus is presented repetitively at a predefined flickering rate and typically elicits a continuous oscillatory brain response at this frequency. This brain response is characterized by an excellent signal-to-noise ratio-a major advantage for source reconstructions. The main goal of present study was to demonstrate the feasibility of this method to study human body perception. To that end, we presented pictures of bodies and contrasted the resulting SSVEPs to two control conditions, i.e., non-objects and pictures of everyday objects (chairs). We found specific SSVEPs amplitude differences between bodies and both control conditions. Source reconstructions localized the SSVEP generators to a network of temporal, occipital and parietal areas. Interestingly, only body perception resulted in activity differences in middle temporal and lateral occipitotemporal areas, most likely reflecting the EBA/FBA. [ABSTRACT FROM AUTHOR]

Previous research has demonstrated that negative affect influences attentional processes. Here, we investigate whether pre-experimental negative affect predicts a hypervigilant neural response as indicated by increased event-related potential amplitudes in response to neutral and positive visual stimuli. In our study, seventeen male participants filled out the German version of the positive and negative affect schedule (Watson et al. in J Pers Soc Psychol 54:1063-1070, ; Krohne et al. in Diagnostica 42:139-156, ) and subsequently watched positive (erotica, extreme sports, beautiful women) and neutral (daily activities) photographs while electroencephalogram was recorded. In line with our hypothesis, low state negative affect but not (reduced) positive affect predicted an increase in the first positive event-related potential amplitude P1 as a typical marker of increased selective attention. As this effect occurred in response to non-threatening picture conditions, negative affect may foster an individual's general hypervigilance, a state that has formerly been associated with psychopathology only. [ABSTRACT FROM AUTHOR]

Over the last decades, frontal alpha asymmetries observed during resting state periods of several minutes have been used as a marker of affective-motivational states. To date, there is no evidence that alpha asymmetries can be observed in response to brief affective-motivational stimuli, as typically presented in event-related designs. As we argue, frontal alpha asymmetry might indeed be elicited by brief events if they are salient enough. In an event-related design, we used erotic pictures, i.e., highly salient incentives to elicit approach motivation, and contrasted them with pictures of dressed attractive women. As expected, we found significant alpha asymmetries for erotic pictures as compared to control pictures. Our findings suggest that the highly reactive reward system can lead to immediate, phasic changes in frontal alpha asymmetries. We discuss the findings with respect to the notion that high salience of erotic pictures derives from their potential of satisfying an individuals' need by mere visual inspection, which is not the case for pictures showing other types of motivational stimuli such as food. [ABSTRACT FROM AUTHOR]

Computational and experimental research has revealed that auditory sensory predictions are derived from regularities of the current environment by using internal generative models. However, so far, what has not been addressed is how the auditory system handles situations giving rise to redundant or even contradictory predictions derived from different sources of information. To this end, we measured error signals in the event-related brain potentials (ERPs) in response to violations of auditory predictions. Sounds could be predicted on the basis of overall probability, i.e., one sound was presented frequently and another sound rarely. Furthermore, each sound was predicted by an informative visual cue. Participants' task was to use the cue and to discriminate the two sounds as fast as possible. Violations of the probability based prediction (i.e., a rare sound) as well as violations of the visual-auditory prediction (i.e., an incongruent sound) elicited error signals in the ERPs (Mismatch Negativity [MMN] and Incongruency Response [IR]). Particular error signals were observed even in case the overall probability and the visual symbol predicted different sounds. That is, the auditory system concurrently maintains and tests contradictory predictions. Moreover, if the same sound was predicted, we observed an additive error signal (scalp potential and primary current density) equaling the sum of the specific error signals. Thus, the auditory system maintains and tolerates functionally independently represented redundant and contradictory predictions. We argue that the auditory system exploits all currently active regularities in order to optimally prepare for future events. [ABSTRACT FROM AUTHOR]

The repetition of an object stimulus results in faster and better recognition of this object (repetition priming). This phenomenon is neuronally associated with a reduced firing rate of neurons (repetition suppression). It has been interpreted as a sharpening mechanism within the cell assembly representing the object. In the case of an unfamiliar stimulus for which no object representation exists, the repetition of the stimulus results in an increase in the firing rate (repetition enhancement).It has been hypothesized that this increase reflects the formation of a cortical object representation. We aimed to investigate cortical object representations as well as repetition suppression and enhancement by means of the steady-state visual evoked potential (SSVEP) in the healthy human brain. To that end, we used a repetition paradigm with familiar and unfamiliar objects, each presented with 12-Hz flicker, producing an oscillatory brain response at the same frequency (i.e. an SSVEP). Results showed significantly smaller SSVEP amplitudes for repeated familiar objects compared to their first presentation (repetition suppression). For unfamiliar objects, SSVEP amplitudes increased with stimulus repetition (repetition enhancement). Source reconstruction revealed inferior temporal regions as generators for the repetition suppression effect, probably reflecting a sharpening mechanism within the cortical representations of the constituting features of an object. In contrast, repetition enhancement was localised in the superior parietal lobe, possibly reflecting the formation of a structural object representation. Thus, the mechanisms underlying repetition priming (i.e. sharpening and formation) depend on the semantic content of the incoming information. [ABSTRACT FROM AUTHOR]

Conventional neuroscientific methods are inadequate for separating the brain responses related to the simultaneous processing of different parts of a natural scene. In the present human electroencephalogram (EEG) study, we overcame this limitation by tagging concurrently presented backgrounds and objects with different presentation frequencies. As a result, background and object elicited different steady-state visual evoked potentials (SSVEPs), which were separately quantified in the frequency domain. We analyzed the effects of semantic consistency and inconsistency between background and object on SSVEP amplitudes, topography, and tomography [variable resolution electromagnetic tomography (VARETA)]. The results revealed that SSVEPs related to background processing showed higher amplitudes in the consistent as opposed to the inconsistent condition, whereas object-related SSVEPs showed the reversed pattern of effects. Given the SSVEPs' sensitivity to visual attention, the results indicate that semantic inconsistency leads to greater attention focused on the object. If all image parts are semantically related, attention is rather directed to the background. The attentional advantage to inconsistent objects in a scene is likely the result of a mismatch between background-based expectations and semantic object information. A clear lateralization of the consistency effect in the anterior temporal lobes indicates functional hemispheric asymmetries in processing background- and object-related semantic information. In summary, the present study is the first to demonstrate the feasibility of SSVEPs to unravel the respective contributions of concurrent neuronal processes involved in the perception of background and object. [ABSTRACT FROM AUTHOR]

Object recognition is achieved through neural mechanisms reliant on the activity of distributed neural assemblies that are thought to be coordinated by synchronous firing in the gamma-band range (>20 Hz). An outstanding question focuses on the extent to which the role of gamma oscillations in object recognition is dependent on attention. Attentional mechanisms determine the allocation of perceptual resources to objects in complex scenes biasing the outcome of their mutual competitive interactions. Would object-related enhancements in gamma activity also occur for unattended objects when perceptual resources are traded off to the processing of concurrent visual material? The present electroencephalogram study investigated event-related potentials and evoked (time- and phase-locked) and induced (non-time- and phase-locked to stimulus onset) gamma-band activity (GBA) using a visual discrimination task of low or high perceptual load at fixation. The task was performed while task-irrelevant familiar or unfamiliar objects coappeared in the surrounding central area. Attentional focus was kept at fixation by varying perceptual load between trials; in such conditions, only holistic object processing or low-level perceptual processing, requiring little or no attention, are thought to occur. Although evoked GBA remained unmodulated, induced GBA enhancements, specific to familiar object presentations, were observed, thus providing evidence for cortical visual representation of unattended objects. In addition, the effect was mostly driven by object-specific activity under low load, implying that, in cluttered or complex scenes, attentional selection likely plays a more significant role in object representation. [ABSTRACT FROM AUTHOR]

Modulations of oscillatory electroencephalogram(EEG) activity in the induced gamma and theta frequency ranges (induced gamma and theta band responses; iGBRs: >30 Hz; iTBRs: ∼6 Hz) have been associated with retrieval of information from long-term memory. However, the specific functional role of these two forms of oscillatory activity remains unclear. The present study examines theta- and gamma-oscillations within a dual-process framework, which defines ''familiarity'' and ''recollection'' as the two component processes of recognition memory. During encoding, participants were instructed to make ''bigger/smaller than a shoebox'' or ''living/nonliving'' decisions for different object pictures. During retrieval ''old/new'' recognition was followed (for items judged old) by a source discrimination task regarding the decision made for each item at encoding. iGBRs (35-80 Hz; 210-330 msec) were higher for correctly identified ''old'' relative to ''new'' objects. Importantly, they did not distinguish between successful and unsuccessful source judgments. In contrast, iTBRs (4-7.5 Hz; 600-1200 msec) were sensitive to source discrimination. We propose that iGBRs mirror early associative processes linked to familiarity-related retrieval processes, whereas iTBRs reflect later onsetting, episodic, recollection-related mechanisms. [ABSTRACT FROM AUTHOR]

The formation of cortical object representations requires the activation of cell assemblies, correlated by induced oscillatory bursts of activity > 20 Hz (induced gamma band responses; iGBRs). One marker of the functional dynamics within such cell assemblies is the suppression of iGBRs elicited by repeated stimuli. This effect is commonly interpreted as a signature of ‘sharpening’ processes within cell-assemblies, which are behaviourally mirrored in repetition priming effects. The present study investigates whether the sharpening of primed objects is an automatic consequence of repeated stimulus processing, or whether it depends on task demands. Participants performed either a ‘living/non-living’ or a ‘bigger/smaller than a shoebox’ classification on repeated pictures of everyday objects. We contrasted repetition-related iGBR effects after the same task was used for initial and repeated presentations (no-switch condition) with repetitions after a task-switch occurred (switch condition). Furthermore, we complemented iGBR analysis by examining other brain responses known to be modulated by repetition-related memory processes (evoked gamma oscillations and event-related potentials; ERPs). The results obtained for the ‘no-switch’ condition replicated previous findings of repetition suppression of iGBRs at 200–300 ms after stimulus onset. Source modelling showed that this effect was distributed over widespread cortical areas. By contrast, after a task-switch no iGBR suppression was found. We concluded that iGBRs reflect the sharpening of a cell assembly only within the same task. After a task switch the complete object representation is reactivated. The ERP (220–380 ms) revealed suppression effects independent of task demands in bilateral posterior areas and might indicate correlates of repetition priming in perceptual structures. [ABSTRACT FROM AUTHOR]

Up to today, the neuronal bases of activating and establishing a memory trace are not well understood. Several findings point towards the idea that the activation of an engram is mirrored in induced oscillatory bursts in the gamma frequency range (> 20 Hz; induced gamma band responses; iGBRs). In the present study, we further investigated this hypothesis. Volunteers performed two tasks on repeated pictures of familiar and unfamiliar objects. They either made a familiarity decision with repetition being task irrelevant (indirect memory task), or a recognition judgment with repetition being task relevant (direct memory task). Furthermore, we complemented iGBR analyses by investigating other brain responses known to be modulated by mnemonic manipulations, namely, evoked gamma oscillations, lower frequency oscillations, and event-related potentials (ERPs). The results obtained for the indirect task replicated previous findings of repetition suppression of iGBRs for repeated familiar stimuli and an increase of iGBRs for repeated unfamiliar objects. These effects might be linked to the ‘sharpening’ of a cell assembly representing a familiar object and to the formation of a new object representation for unfamiliar stimuli, respectively. In contrast, the direct task revealed no repetition-related modulations of iGBRs. Thus, modulations of iGBRs are not a mere automatic consequence of repeated stimulus processing but might rather mirror changes within cortical object representation according to use-dependent plasticity principles. Furthermore, evoked gamma responses, lower frequency bands, and late components of the ERPs correlated with more specific subprocesses during mnemonic functioning. [Copyright &y& Elsevier]

Cortical object representations seem to require the formation of neural cell assemblies. The physiological correlate of cell assembly activity may be seen in synchronized neural activity in the gamma band range. The improvement in perceiving and identifying an object by experience is commonly referred to as repetition priming. One possible neural mechanism for repetition priming is ‘repetition suppression’ within a cell assembly coding the stimulus. The present electroencephalogram study was designed to investigate oscillatory brain activity when line drawings of concrete objects were repeated either immediately after a first presentation or after intervening a number of different stimuli. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial picture presentation. Repeated presentations of the same picture led to a significant decrease of induced gamma power. Furthermore, repeated presentations of the same object resulted in a decrease in phase synchrony between distant electrode sites. No significant repetition effects were found in the alpha or beta frequency range. The event-related potential (ERP), which was also modulated by priming, showed a different scalp distribution compared with induced GBRs. In addition, ERP repetition effects decayed at larger intervals between initial and repeated presentations, whereas induced GBRs were not modulated as a function of stimulus lag. We concluded that the decrease in amplitude of induced GBRs and the reduction of gamma phase synchrony between pairs of electrodes after repeated picture presentations might be linked to a ‘sharpening’ mechanism within a cell assembly representing an object. [ABSTRACT FROM AUTHOR]

Repeated experience with an object due to prior exposure to that object is commonly referred to as perceptual or repetition priming. One possible neuronal mechanism for repetition priming is ‘repetition suppression’ within a cell assembly coding the stimulus. Recently, induced gamma band responses (GBRs) were discussed as a possible physiological correlate of activity in such a cell assembly. The present EEG study was designed to investigate the modulation of induced GBRs when line drawings were presented either once or consecutively two or three times. Results showed a broad distribution of spectral gamma power and synchrony after initial picture presentation. Repeated presentations of the same picture led to a decrease of induced gamma power and less synchronized activity between distant electrode sites. The decrease of induced GBRs and synchrony after repeated picture presentations may be linked to a ‘neural savings’ mechanism within a cell assembly representing an object. Furthermore, the visual evoked potential, which was modulated by priming, showed a topographically different distribution compared to induced GBRs. [Copyright &y& Elsevier]

Abstract: In a crowded scene we can effectively focus our attention on a specific speaker while largely ignoring sensory inputs from other speakers. How attended speech inputs are extracted from similar competing information has been primarily studied in the auditory domain. Here we examined the deployment of visuo-spatial attention in multiple speaker scenarios. Steady-state visual evoked potentials (SSVEP) were monitored as a real-time index of visual attention towards three competing speakers. Participants were instructed to detect a target syllable by the center speaker and ignore syllables from two flanking speakers. The study incorporated interference trials (syllables from three speakers), no-interference trials (syllable from center speaker only), and periods without speech stimulation in which static faces were presented. An enhancement of flanking speaker induced SSVEP was found 70–220 ms after sound onset over left temporal scalp during interference trials. This enhancement was negatively correlated with the behavioral performance of participants - those who showed largest enhancements had the worst speech recognition performance. Additionally, poorly performing participants exhibited enhanced flanking speaker induced SSVEP over visual scalp during periods without speech stimulation. The present study provides neurophysiologic evidence that the deployment of visuo-spatial attention to flanking speakers interferes with the recognition of multisensory speech signals under noisy environmental conditions. [Copyright &y& Elsevier]

Abstract: Multiple objects in a visual scene compete for neuronal representation. We investigated competitive neuronal dynamics in cortical networks of early visual processing in the human brain. Coloured picture streams flickered at 7.42 Hz, evoking the steady-state visual evoked potential (SSVEP), an electrophysiological response of neuronal populations in early visual areas synchronised by the external pacemaker. While these picture streams were at a fixed location in the upper left and right quadrant, respectively, additional competing picture streams flickering at a different frequency were continuously changing the distance to the stationary streams by slow motion. Analysis of the 7.42 Hz SSVEP amplitude revealed significant amplitude decreases when the competing stimulus was closer than about 4.5° of visual angle. Sources of the SSVEP suppression effect were found in early visual areas of the ventral and dorsal processing streams. Attending the stationary stimulus resulted in no difference in 7.42 Hz SSVEP amplitude regardless of spatial separation to the competing stimulus. Contrary to the predictions of the model, we found co-amplification of the competing stimulus at close spatial proximity accompanied by an increase of an intermodulation frequency, suggesting integrated neuronal processing of target and competing stimuli when both streams are close together. [Copyright &y& Elsevier]

Abstract: Frequency specific synchronisation of neuronal firing within the gamma-band (30–70Hz) appears to be a fundamental correlate of both basic sensory and higher cognitive processing. In-vitro studies suggest that the neurochemical basis of gamma-band oscillatory activity is based on interactions between excitatory (i.e. glutamate) and inhibitory (i.e. GABA) neurotransmitter concentrations. However, the nature of the relationship between excitatory neurotransmitter concentration and changes in gamma band activity in humans remains undetermined. Here, we examine the links between dynamic glutamate concentration and the formation of functional gamma-band oscillatory networks. Using concurrently acquired event-related magnetic resonance spectroscopy and electroencephalography, during a repetition-priming paradigm, we demonstrate an interaction between stimulus type (object vs. abstract pictures) and repetition in evoked gamma-band oscillatory activity, and find that glutamate levels within the lateral occipital cortex, differ in response to these distinct stimulus categories. Importantly, we show that dynamic glutamate levels are related to the amplitude of stimulus evoked gamma-band (but not to beta, alpha or theta or ERP) activity. These results highlight the specific connection between excitatory neurotransmitter concentration and amplitude of oscillatory response, providing a novel insight into the relationship between the neurochemical and neurophysiological processes underlying cognition. [Copyright &y& Elsevier]

Abstract: In present high density electroencephalogram (EEG) study, we examined steady-state visual evoked potential (SSVEP) correlates of object recognition. In SSVEP tasks a visual stimulus is presented repetitively at a specific flickering rate and typically elicits a continuous oscillatory brain response. This response is characterized by the same fundamental frequency as the initiating stimulus. The stimulus material consisted of a series of pictures depicting familiar and unfamiliar objects which have been successfully applied in previous EEG studies on object recognition. In particular, we presented familiar and unfamiliar objects at rates of 7.5, 12 and 15Hz. At all three driving frequencies, we found specific SSVEPs that furthermore showed significant amplitude differences between familiar and unfamiliar objects. The familiar/unfamiliar effects were localized to early occipital, lateral occipital and temporal areas by means of VARETA (Variable Resolution Electromagnetic Tomography). Interestingly, the morphology of the familiar/unfamiliar effect differed between flicker rates. The 12 and 15Hz conditions revealed higher SSVEP amplitudes for familiar as opposed to unfamiliar objects, whereas in the 7.5Hz condition the effect was reversed. We concluded that SSVEPs are sensitive to stimuli''s semantic content. Thus, SSVEP paradigms open new venues to study object recognition. Nonetheless, selecting appropriate driving frequencies is non-trivial, because flicker rate might have an influence on the observed effects. [Copyright &y& Elsevier]

Abstract: This study proposes a standard paradigm for the investigation of visual information processing by means of gamma activity and presents a novel set of stimuli with a broad range of complex, coloured familiar real world and unfamiliar nonsense objects which are well matched with respect to physical stimulus properties. In order to demonstrate that the paradigm and stimulus set yield reliable results both were employed in two electrophysiological investigations in two independent laboratories. Participants were required to discriminate familiar from unfamiliar stimuli. The pattern of results was very consistent across laboratories. Early event-related potentials were not influenced by the stimulus type suggesting that physical stimulus properties did not confound object familiarity. Induced gamma band activity was stronger for familiar than for unfamiliar objects, supporting the notion of gamma activity as a signature of cortical networks underlying object representations. [Copyright &y& Elsevier]

Steady-state somatosensory evoked potentials (SSSEPs) were recorded from the scalp of human subjects elicited by 20 and 26 Hz mechanical vibrations applied simultaneously to the index finger of the left (20 Hz) and right hand (26 Hz). Subjects were instructed to attend to the flutter vibration at one finger while ignoring the other finger and to detect rare target events at the to-be-attended finger. The amplitude of the frequency coded SSSEP elicited by the attended vibration was significantly enlarged when attention was focused at the respective finger. This amplitude enhancement with attention was most prominent over fronto-central electrode locations contralateral to the attended finger. This is the first report to show the attentional modulation of the SSSEP amplitude in humans, suggesting an enhancement of neural responses in the sense of flutter with attention. The findings will open a new approach for studying the neural mechanisms of sustained selective attention in somatosensation. [Copyright &y& Elsevier]