Effects of stereoscopic disparity on early ERP components during classification of three-dimensional objects

The human brain deals with violating general color or depth knowledge in different time courses

Utilizing the high temporal resolution of event-related potentials (ERPs), we compared the time course of processing incongruent color versus 3D-depth information. Participants were asked to judge whether the food color (color condition) or 3D structure (3D-depth condition) was congruent or incongruent with their previous knowledge and experience. The behavioral results showed that the reaction times in the congruent 3D-depth condition were slower than those in the congruent color condition. The reaction times in the incongruent 3D-depth condition were slower than those in the incongruent color condition. The ERP results showed that incongruent color stimuli induced a larger N270, larger P300, and smaller N400 components in the fronto-central region than the congruent color stimuli. Incongruent 3D-depth stimuli induced a smaller N1 in the occipital region, larger P300 and smaller N400 in the parietal-occipital region than congruent 3D-depth stimuli. The time-frequency analysis found that incongruent color stimuli induced a larger theta band (360-580 ms) activation in the fronto-central region than congruent color stimuli. Incongruent 3D-depth stimuli induced larger alpha and beta bands (240-350 ms) activation in the parietal region than congruent 3D-depth stimuli. Our results suggest that the human brain deals with violating general color or depth knowledge in different time courses. We speculate that the depth perception conflict was dominated by solving the problem with visual processing, whereas the color perception conflict was dominated by solving the problem with semantic violation.

Brain activity underlying visual search in depth when viewing volumetric multiplanar images

The study investigated the cortical activity associated with 3D and 2D image perception on a volumetric multiplanar display by analyzing event-related potentials (ERPs) and power spectral density (PSD). In this study, we used a volumetric multiplanar display to present visual targets, and the brain signals were recorded via an EEG amplifier and analyzed using the EEGLAB toolbox on MATLAB. The study found no significant differences in amplitude between the 3D and 2D conditions across five occipital and parietal electrodes. However, there was a significant difference in latency of the P3 component on the Pz electrode. The analysis of PSD showed no significant differences between the two conditions, although there was a slightly higher alpha and beta activity observed in the 2D visualization. The study concluded that 3D image representation on a volumetric multiplanar display has no more sensory or cognitive load on the human brain than 2D representation, and that depth perception on a multiplanar display requires less brain activity.

Up close and emotional: Electrophysiological dynamics of approaching angry faces

Recent evidence suggests that looming emotional faces are processed rapidly by the neural system, and that this apparent approach further interacts with emotion, causing an enhanced neural response for angry expressions. However, previous research has not demonstrated unequivocally if these effects are due to low-level visual features, or if they are indeed due to the emotional content of the stimuli. To address this question, the current study presented upright and inverted angry and neutral faces, which either expanded or contracted in size on a constant depth-cued background, such that they appeared to approach or retreat from the viewer. EEG/ERP measures were used to identify the time course of brain activity for these stimuli. The results showed that when faces were upright, both the P1 and N170 were enhanced for angry expressions, with the P1 being further increased with looming angry faces. The inversion of the faces caused an increase in both the P1 and N170 amplitudes, but no modulation was found for emotions. These findings show an early modulation of brain activity for upright looming angry faces and rule out the influence of low-level visual features as a contributing factor.

Neural Research on Depth Perception and Stereoscopic Visual Fatigue in Virtual Reality

Virtual reality (VR) technology provides highly immersive depth perception experiences; nevertheless, stereoscopic visual fatigue (SVF) has become an important factor currently hindering the development of VR applications. However, there is scant research on the underlying neural mechanism of SVF, especially those induced by VR displays, which need further research. In this paper, a Go/NoGo paradigm based on disparity variations is proposed to induce SVF associated with depth perception, and the underlying neural mechanism of SVF in a VR environment was investigated. The effects of disparity variations as well as SVF on the temporal characteristics of visual evoked potentials (VEPs) were explored. Point-by-point permutation statistical with repeated measures ANOVA results revealed that the amplitudes and latencies of the posterior VEP component P2 were modulated by disparities, and posterior P2 amplitudes were modulated differently by SVF in different depth perception situations. Cortical source localization analysis was performed to explore the original cortex areas related to certain fatigue levels and disparities, and the results showed that posterior P2 generated from the precuneus could represent depth perception in binocular vision, and therefore could be performed to distinguish SVF induced by disparity variations. Our findings could help to extend an understanding of the neural mechanisms underlying depth perception and SVF as well as providing beneficial information for improving the visual experience in VR applications.

Investigate the Neuro Mechanisms of Stereoscopic Visual Fatigue

Stereoscopic visual fatigue (SVF) due to prolonged immersion in the virtual environment can lead to negative user experience, thus hindering the development of virtual reality (VR) industry. Previous studies have focused on investigating the evaluation indicators associated with SVF, while few studies have been conducted to reveal the underlying neural mechanism, especially in VR applications. In this paper, a modified Go/NoGo paradigm was adopted to induce SVF in VR environment with Go trials for maintaining participants' attention to experimental viewing tasks and NoGo trials for investigating the neural effects under SVF. Random dot stereograms (RDSs) with 11 disparities and 2 types of shapes (arrow and rectangle) were presented to evoke the depth-related visual evoked potentials (DVEPs) during 64-channel EEG recordings. EEG datasets collected from 15 participants in NoGo trials were selected to conduct individual processing and group analysis, in which the characteristics of the DVEPs components for various fatigue degrees were compared with one-way repeated-measurement ANOVA and independent components were clustered to explore the original cortex areas related to SVF. Point-by-point permutation statistics revealed that DVEPs sample points from 230ms to 280ms in most brain areas changed significantly with SVF. More specifically, we found that amplitudes of component P2 changed significantly when SVF increased. Additionally, independent component analysis (ICA) identified that component P2 which originated from posterior cingulate cortex and precuneus, was associated statistically with SVF. We believe that SVF is rather a conscious status concerning the changes of self-awareness or self-location awareness than the performance reduction of retinal image processing. Moreover, we suggest that indicators representing higher conscious state may be a better indicator for SVF evaluation in VR environments.

Neural responses to reflection symmetry for shapes defined by binocular disparity, and for shapes perceived as regions of background

Human perception of symmetry is associated with activation in an extended network of extrastriate visual areas. This activation generates an ERP called the Sustained Posterior Negativity (SPN). In most studies so far, the stimuli have been defined by luminance. We tested whether the SPN is present when stimuli are defined by stereoscopic disparity using random dot stereograms (RDS). In Experiment 1, we compared the SPN signal for contours specified by binocular disparity and contours specified by monocular cues. The SPN was equivalent, suggesting that the type of contour does not alter the SPN signal. In Experiment 2 we exploited the unique property of RDS to provide unambiguous figure-ground arrangements. Psychophysical work has shown that symmetry is more easily detected when it is a property of a single object (i.e., within a figure), compared to a property of a gap between two objects (i.e., the ground). Therefore, the target regions in this experiment could either be foreground or background. The SPN onset was delayed when the symmetry was in a ground region. This may be because object formation interferes with the processing of shape information in the ground region.

Investigate the 3D Visual Fatigue Using Modified Depth-Related Visual Evoked Potential Paradigm

Prolonged viewing of 3D content may result in severe fatigue symptoms, giving negative user experience thus hindering the development of 3D industry. For 3D visual fatigue evaluation, previous studies focused on exploring the changes of frequency-domain features in EEG for various fatigue degrees. However, their time-domain features were scarcely investigated. In this study, a modified paradigm with a random disparities order is adopted to evoke the depth-related visual evoked potentials (DVEPs). Then the characteristics of the DVEPs components for various fatigue degrees are compared using one-way repeated-measurement ANOVA. Point-by-point permutation statistics revealed sample points from 100ms to 170ms - including P1 and N1 - in sensors Pz and P4 changed significantly with visual fatigue. More specifically, we find that the amplitudes of P1 and N1 change significantly when visual fatigue increases. Additionally, independent component analysis identify P1 and N1 which originate from posterior cingulate cortex are associated statistically with 3D visual fatigue. Our results indicate there is a significant correlation between 3D visual fatigue and P1 amplitude, as well as N1, of DVEPs on right parietal areas. We believe the characteristics (e.g., amplitude and latency) of identified components may be the indicators of 3D visual fatigue evaluation. Furthermore, we argue that 3D visual fatigue may be associated with the activities decrease of the attention and the processing capacity of disparity.

Distinct visuo-motor brain dynamics for real-world objects versus planar images

Ultimately, we aim to generalize and translate scientific knowledge to the real world, yet current understanding of human visual perception is based predominantly on studies of two-dimensional (2-D) images. Recent cognitive-behavioral evidence shows that real objects are processed differently to images, although the neural processes that underlie these differences are unknown. Because real objects (unlike images) afford actions, they may trigger stronger or more prolonged activation in neural populations for visuo-motor action planning. Here, we recorded electroencephalography (EEG) when human observers viewed real-world three-dimensional (3-D) objects or closely matched 2-D images of the same items. Although responses to real objects and images were similar overall, there were critical differences. Compared to images, viewing real objects triggered stronger and more sustained event-related desynchronization (ERD) in the μ frequency band (8-13 Hz) - a neural signature of automatic motor preparation. Event-related potentials (ERPs) revealed a transient, early occipital negativity for real objects (versus images), likely reflecting 3-D stereoscopic differences, and a late sustained parietal amplitude modulation consistent with an 'old-new' memory advantage for real objects over images. Together, these findings demonstrate that real-world objects trigger stronger and more sustained action-related brain responses than images do. The results highlight important similarities and differences between brain responses to images and richer, more ecologically relevant, real-world objects.

Early sensitivity of evoked potentials to surface and volumetric structure during the visual perception of three-dimensional object shape

This study used event-related potentials (ERPs) to elucidate how the human visual system processes three-dimensional (3-D) object shape structure. In particular, we examined whether the perceptual mechanisms that support the analysis of 3-D shape are differentially sensitive to higher order surface and volumetric part structure. Observers performed a whole-part novel object matching task in which part stimuli comprised sub-regions of closed edge contour, surfaces or volumetric parts. Behavioural response latency data showed an advantage in matching surfaces and volumetric parts to whole objects over contours, but no difference between surfaces and volumes. ERPs were analysed using a convergence of approaches based on stimulus dependent amplitude modulations of evoked potentials, topographic segmentation, and spatial frequency oscillations. The results showed early differential perceptual processing of contours, surfaces, and volumetric part stimuli. This was first reliably observed over occipitoparietal electrodes during the N1 (140-200 ms) with a mean peak latency of 170 ms, and continued on subsequent P2 (220-260 ms) and N2 (260-320 ms) components. The differential sensitivity in perceptual processing during the N1 was accompanied by distinct microstate patterns that distinguished among contours, surfaces and volumes, and predominant theta band activity around 4-7 Hz over right occipitoparietal and orbitofrontal sites. These results provide the first evidence of early differential perceptual processing of higher order surface and volumetric shape structure within the first 200 ms of stimulus processing. The findings challenge theoretical models of object recognition that do not attribute functional significance to surface and volumetric object structure during visual perception.

Stereo viewing modulates three-dimensional shape processing during object recognition: A high-density ERP study

The role of stereo disparity in the recognition of 3-dimensional (3D) object shape remains an unresolved issue for theoretical models of the human visual system. We examined this issue using high-density (128 channel) recordings of event-related potentials (ERPs). A recognition memory task was used in which observers were trained to recognize a subset of complex, multipart, 3D novel objects under conditions of either (bi-) monocular or stereo viewing. In a subsequent test phase they discriminated previously trained targets from untrained distractor objects that shared either local parts, 3D spatial configuration, or neither dimension, across both previously seen and novel viewpoints. The behavioral data showed a stereo advantage for target recognition at untrained viewpoints. ERPs showed early differential amplitude modulations to shape similarity defined by local part structure and global 3D spatial configuration. This occurred initially during an N1 component around 145-190 ms poststimulus onset, and then subsequently during an N2/P3 component around 260-385 ms poststimulus onset. For mono viewing, amplitude modulation during the N1 was greatest between targets and distracters with different local parts for trained views only. For stereo viewing, amplitude modulation during the N2/P3 was greatest between targets and distracters with different global 3D spatial configurations and generalized across trained and untrained views. The results show that image classification is modulated by stereo information about the local part, and global 3D spatial configuration of object shape. The findings challenge current theoretical models that do not attribute functional significance to stereo input during the computation of 3D object shape. (PsycINFO Database Record