Left-Hemispheric Asymmetry for Object-Based Attention: an ERP Study

Asymmetries in event-related potentials part 1: A systematic review of face processing studies

The human brain shows distinct lateralized activation patterns for a range of cognitive processes. One such function, which is thought to be lateralized to the right hemisphere (RH), is human face processing. Its importance for social communication and interaction has led to a plethora of studies investigating face processing in health and disease. Temporally highly resolved methods, like event-related potentials (ERPs), allow for a detailed characterization of different processing stages and their specific lateralization patterns. This systematic review aimed at disentangling some of the contradictory findings regarding the RH specialization in face processing focusing on ERP research in healthy participants. Two databases were searched for studies that investigated left and right electrodes while participants viewed (mostly neutral) facial stimuli. The included studies used a variety of different tasks, which ranged from passive viewing to memorizing faces. The final data selection highlights, that strongest lateralization to the RH was found for the N170, especially for right-handed young male participants. Left-handed, female, and older participants showed less consistent lateralization patterns. Other ERP components like the P1, P2, N2, P3, and the N400 were overall less clearly lateralized. The current review highlights that many of the assumed lateralization patterns are less clear than previously thought and that the variety of stimuli, tasks, and EEG setups used, might contribute to the ambiguous findings.

Event-related brain potential markers of visual and auditory perception: A useful tool for brain computer interface systems

OBJECTIVE

A majority of BCI systems, enabling communication with patients with locked-in syndrome, are based on electroencephalogram (EEG) frequency analysis (e.g., linked to motor imagery) or P300 detection. Only recently, the use of event-related brain potentials (ERPs) has received much attention, especially for face or music recognition, but neuro-engineering research into this new approach has not been carried out yet. The aim of this study was to provide a variety of reliable ERP markers of visual and auditory perception for the development of new and more complex mind-reading systems for reconstructing the mental content from brain activity.

METHODS

A total of 30 participants were shown 280 color pictures (adult, infant, and animal faces; human bodies; written words; checkerboards; and objects) and 120 auditory files (speech, music, and affective vocalizations). This paradigm did not involve target selection to avoid artifactual waves linked to decision-making and response preparation (e.g., P300 and motor potentials), masking the neural signature of semantic representation. Overall, 12,000 ERP waveforms × 126 electrode channels (1 million 512,000 ERP waveforms) were processed and artifact-rejected.

RESULTS

Clear and distinct category-dependent markers of perceptual and cognitive processing were identified through statistical analyses, some of which were novel to the literature. Results are discussed from the view of current knowledge of ERP functional properties and with respect to machine learning classification methods previously applied to similar data.

CONCLUSION

The data showed a high level of accuracy (p ≤ 0.01) in the discriminating the perceptual categories eliciting the various electrical potentials by statistical analyses. Therefore, the ERP markers identified in this study could be significant tools for optimizing BCI systems [pattern recognition or artificial intelligence (AI) algorithms] applied to EEG/ERP signals.

An efficient 3D column-only P300 speller paradigm utilizing few numbers of electrodes and flashings for practical BCI implementation

The event related P300 potentials, positive waveforms in electroencephalography (EEG) signals, are often utilized in brain computer interfaces (BCI). Many studies have been carried out to improve the performance of P300 speller systems either by developing signal processing algorithms and classifiers with different architectures or by designing new paradigms. In this study, a new paradigm is proposed for this purpose. The proposed paradigm combines two remarkable properties of being a 3D animation and utilizing column-only flashings as opposed to classical paradigms which are based on row-column flashings in 2D manner. The new paradigm is utilized in a traditional two-layer artificial neural networks model with a single output neuron, and numerous experiments are conducted to evaluate and compare the performance of the proposed paradigm with that of the classical approach. The experimental results, including statistical significance tests, are presented for single and multiple EEG electrode usage combinations in 1, 3 and 15 flashing repetitions to detect P300 waves as well as to recognize target characters. Using the proposed paradigm, the best average classification accuracy rates on the test data are improved from 89.97% to 93.90% (an improvement of 4.36%) for 1 flashing, from 97.11% to 98.10% (an improvement of 1.01%) for 3 flashings and from 99.70% to 99.81% (an improvement of 0.11%) for 15 flashings when all electrodes, included in the study, are utilized. On the other hand, the accuracy rates are improved by 9.69% for 1 flashing, 4.72% for 3 flashings and 1.73% for 15 flashings when the proposed paradigm is utilized with a single EEG electrode (P8). It is observed that the proposed speller paradigm is especially useful in BCI systems designed for few EEG electrodes usage, and hence, it is more suitable for practical implementations. Moreover, all participants, given a subjective test, declared that the proposed paradigm is more user-friendly than classical ones.

Left hemispheric stroke in a professional artist: A prospective case study

Several papers have investigated the effect of stroke on creativity. While initial evidence favored right hemispheric dominance in artwork creation, subsequent well-founded research has established the left hemispheric participation in creativity, supporting the idea of bi-hemispheric role in artistic production. We here describe the case of a renowned artist who suffered a left hemispheric ischemic stroke involving the occipito-temporal region and subsequently manifested several difficulties in producing visual artworks. We documented his recovery phases in a prospective way during the initial months following stroke and observed that, although his constructional abilities recovered to a significant extent over 3 months, spontaneous creation was persistently impaired. The right hemispheric role in visual art is linked mainly to visuo-spatial skills and global attention, while left hemispheric participation is thought to be related to focal attention and visual imagery. Our case study lends support to the idea that art is a bi-hemispheric function with important complementary contributions from both the right and left hemisphere.

Hemispheric Asymmetry in Visual Processing: An ERP Study on Spatial Frequency Gratings

A hemispheric asymmetry for the processing of global versus local visual information is known. In this study, we investigated the existence of a hemispheric asymmetry for the visual processing of low versus high spatial frequency gratings. The event-related potentials were recorded in a group of healthy right-handed volunteers from 30 scalp sites. Six types of stimuli (1.5, 3 and 6 c/deg gratings) were randomly flashed 180 times in the left and right upper hemifields. The stimulus duration was 80 ms, and the interstimulus interval (ISI) ranged between 850 and 1000 ms. Participants paid attention and responded to targets based on their spatial frequency and location. The C1 and P1 visual responses, as well as a later selection negativity and a P300 component of event-related potentials (ERPs), were quantified and subjected to repeated-measure analyses of variance (ANOVAs). Overall, the performance was faster for the right visual field (RVF), thus suggesting a left hemispheric advantage for the attentional selection of local elements. Similarly, the analysis of the mean area amplitude of the C1 (60–110 ms) sensory response showed a stronger attentional effect (F+L+ vs. F−L+) at the left occipital areas, thus suggesting the sensory nature of this hemispheric asymmetry.

ERP indices of an orientation-dependent recognition of the human body schema

While it is well-established that the face perception is orientation-dependent, less evidence has been provided on the effects of the orientation on the body schema processing and related attentive mechanisms. Poorer performance in same/different judgment tasks and increased occipito-temporal N1 response to the inverted (vs. upright) body schema seem to hint at an orientation-dependent perceptual mechanism. The present electrophysiological study investigated the role of attentive selection processes required to recognize the inverted (vs. upright) body schema by means of the event-related potentials (ERP). 320 different images depicting body shapes (wooden dummies) as opposed to random structures of cubes were created in 3D graphics. Thirty-two right-handed participants were presented with the stimuli in an upright and inverted orientation. They were required to alternatively recognize one of the two categories of stimuli (by button press) regardless of the orientation, during EEG recording. The body inversion led to increased reaction times during body schema recognition. A slower anterior N2, larger N1, Selection Negativity (SN), and increased parietal P300 components were elicited by the perception of the inverted body schema. Slower stimulus processing and increased attention allocation were associated with the processing of the inverted body schema. The swLORETA source reconstruction (in the SN time window) showed enhanced engagement of prefrontal, limbic, and temporal regions during the perception of the inverted body schema. At the same time, the cubes' orientation did not affect ERP amplitudes. Overall, these pieces of evidence seem to suggest a crucial role of the upright orientation in the visual recognition of the human body schema.

From Correlational Signs to Markers. Current Trends in Neuroelectric Research on Visual Attentional Processing

Traditionally, electroencephalographic (EEG) and event-related brain potentials (ERPs) research on visual attentional processing attempted to account for mental processes in conceptual terms without reference to the way in which they were physically realized by the anatomical structures and physiological processes of the human brain. The brain science level of analysis, in contrast, attempted to explain the brain as an information processing system and to explain mental events in terms of brain processes. Somehow overcoming the separation between the two abovementioned levels of analysis, the cognitive neuroscience level considered how information was represented and processed in the brain. Neurofunctional processing takes place in a fraction of a second. Hence, the very high time resolution and the reliable sensitivity of EEG and ERPs in detecting fast functional changes in brain activity provided advantages over hemodynamic imaging techniques such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI), as well as over behavioral measures. However, volume conduction and lack of three-dimensionality limited applications of EEG and ERPs per se more than hemodynamic techniques for revealing locations in which brain processing occurs. These limits could only be overcome by subtraction methods for isolating attentional effects that might endure over time in EEG and may be riding even over several different ERP components, and by intracerebral single and distributed electric source analyses as well as the combining of these signals with high-spatial resolution hemodynamic signals (fMRI), both in healthy individuals and clinical patients. In my view, the articles of the Special Issue concerned with "ERP and EEG Markers of Brain Visual Attentional Processing" of the present journal Brain Sciences provide very good examples of all these levels of analysis.

Muscular effort coding in action representation in ballet dancers and controls: Electrophysiological evidence

The present electrophysiological (EEG) study investigated the neural correlates of perceiving effortful vs. effortless movements belonging to a specific repertoire (ballet). Previous evidence has shown an increased heart and respiratory rate during the observation and imagination of human actions that require a great muscular effort. In addition, TMS (transcranial magnetic stimulation) and EEG studies have evidenced a greater muscle-specific cortical excitability and an increase in late event-related potentials during the observation of effortful actions. In this investigation, fifteen professional female ballet dancers and 15 controls with no experience whatsoever with dance, gymnastics, or martial arts were recruited. They were shown 326 short videos displaying a male dancer performing standard ballet steps that could be either effortful or relatively effortless. Participants were instructed to observe each clip and imagine themselves physically executing the same movement. Importantly, they were blinded to the stimuli properties. The observation of effortful compared with effortless movements resulted in a larger P300 over frontal sites in dancers only, likely because of their visuomotor expertise with the specific steps. Moreover, an enhanced Late Positivity was identified over posterior sites in response to effortful stimuli in both groups, possibly reflecting the processing of larger quantities of visual kinematic information. The source reconstruction swLORETA performed on the Late Positivity component showed greater engagement of frontoparietal regions in dancers, while task-related frontal and occipitotemporal visual regions were more active in controls. It, therefore, appears that, in dancers, effort information was encoded in a more refined manner during action observation and in the absence of explicit instruction. Acquired motor knowledge seems to result in visuomotor resonance processes, which, in turn, underlies enhanced action representation of the observed movements.