The range of stereoscopic perception: influence of binocular summation,interocular differences in optical quality and halo perception

The study of the visual function and optical quality of the eye has become a fundamental aim in the characterization of visual performance, especially in binocular vision, as this is our natural state of visual perception and because of its importance in clinical applications. Interocular asymmetry affects visual performance, and therefore its effect on different visual functions and stereopsis is of interest. In this work, we analyse interocular differences in optical quality (higher order aberrations and Strehl ratio) on the maximum disparity (the total range of stereoscopic perception) under mesopic conditions. We also analyse the relationship between the maximum disparity and the visual-discrimination capacity (halo perception) or binocular summation. The results in normal observers show a deterioration of the range of stereoscopic perception with the interocular differences in optical quality and with a higher perception of halos. Regarding the binocular summation for the visual functions studied, a positive correlation with the maximum disparity is found.     

观察立体影像时的视觉疲劳及其缓解措施

利用两眼视差原理获得立体视的技术存在着诸多问题,其中视觉疲劳是其最为突出的。论文分析了两眼视差立体视产生视觉疲劳的原因和症状;讨论了辐辏和焦点调节不一致的问题;最后提出了不要让眼睛机能负担过度、将焦点调节和辐辏的不一致限制在一个合理的范围内、避免过大的视差和视差的不连续变化、利用补正透镜减轻视觉负担等四种缓解视觉疲劳的措施。     

Starry night: a texture devoid of depth cues

From a modern Bayesian point of view, the classic Julesz random-dot stereogram is a cue-conflict stimulus: Texture cues specify an unbroken, unslanted surface, in conflict with any variation in depth specified by binocular disparity. We introduce a new visual texture-the starry night texture (SNT)--that is incapable of conveying slant, depth edges, or texture boundaries, in a single view. For SNT, changing density is equivalent to changing intensity, so an instance of the texture is characterized (up to the random locations of the texture elements) by what we call its densintensity. We consider deviations from the ideal that are needed to realize the texture in practice. In three experiments with computer-generated stimuli we examined human perception of SNT to show that (1) the deviations from the ideal that were needed to realize SNT do not affect the invariance of its appearance across changes in distance of several orders of magnitude; (2) as predicted, observers match SNT across changes in distance better than other textures; and (3) the use of SNT in a slant perception experiment did not reliably increase observers' reliance on stereoscopic slant cues, as compared with the sparse random-dot displays that have been commonly employed to study human perception of shape from binocular disparity and motion.     

Stereoscopic 3D objects evoke stronger saliency for nonverbal working memory: An fMRI study

Effective working memory (WM) training is often desired to improve WM. Recent studies have suggested that WM training is more successful when participants monitor scenes in three‐dimensional (3D) environments. Although previous neuroimaging studies have examined visuospatial WM in relation to a 3D scene or object, these studies did not investigate WM using stereoscopic 3D object stimuli. We used functional magnetic resonance imaging (fMRI) to identify brain activation during an N‐back task with 3D object stimuli, and determined the difference in activation pattern between stereoscopic versus shaded 3D objects. We found that the anterior insula, ventral striatum, and posterior orbitofrontal cortex showed greater activation during the 2‐back task with stereoscopic 3D objects than with shaded 3D objects. These regions have previously been associated with a salience network.     

A novel method for detection of voxels for decision making: An fMRI study

This study explores the patterns of activation in brain regions toward classifying decision making voxels from among four major Brodmann areas (BAs) upon stimulus of visual tasks. Toward this goal, a well‐known clustering analysis has been performed on real‐time data of the human brain obtained using functional magnetic resonance imaging (fMRI). The functional connectivity among various brain regions was detected by leveraging a distance correlation graph. Graphical methods have been employed to visualize the clusters elicited in the process. The analysis of the results sheds new light on how four significantly activated BAs of the brain exhibit effective connectively to perform a visual task in the context of decision making.     

New fMRI analysis method for multiple stimuli using reference estimation

The stimulation paradigms of a functional MRI (fMRI) usually consist of one or more stimulations and a resting state in the block‐based and event‐related designs. To localize the activation areas in the human brain, each voxel is statistically analyzed using the fMRI data measured with the stimulation. The conventional method can be inefficient for experiments with multiple stimuli because of measuring the resting‐state signals repeatedly, causing redundancy in the scanning process. Although the phase mapping method can be applied to reduce the redundant resting‐state measurements, there are still limitations in the detection of regions activated by multiple stimuli and the periodic sequence of the multiple stimuli. In this article, a new fMRI data analysis method is presented that enables the detection of functional activations without the resting‐state images. This method estimates the reference signal from the signals acquired during multiple stimuli, and a random sequence and various durations of the multiple stimuli can be applied. Therefore, it can be used in the event‐related design as well as the block‐based design. The results of simulation and fMRI experiments show that the proposed method can correctly detect the activation regions of multiple stimuli, even for overlap regions, and can reduce the imaging time by skipping the resting‐state imaging. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 315–322, 2011     

Integration, segregation, and binocular combination

The human visual system can accurately judge the mean of a distribution of different orientation samples. We ask whether the site of this integration is before or after the sites of binocular combination and disparity processing. Furthermore, we are interested in whether the efficiency with which local orientation information is integrated depends on the eye of origin. Our results suggest that orientation integration occurs after binocular integration but before disparity coding. We show that the effectiveness of added orientation noise is not only less than expected on signal or noise grounds but also that it depends on the dominance of the eye to which it is presented, suggesting an interocular opponent interaction in which the dominant eye input has higher gain.     

Variations in BOLD response latency estimated from event‐related fMRI at 3T: Comparisons between gradient‐echo and Spin‐echo

Functional magnetic resonance imaging (fMRI) commonly uses gradient‐recalled echo (GRE) signals to detect regional hemodynamic variations originating from neural activities. While the spatial localization of activation shows promising applications, indexing temporal response remains a poor mechanism for detecting the timing of neural activity. Particularly, the hemodynamic response may fail to resolve sub‐second temporal differences between brain regions because of its signal origin or noise in data, or both. This study aimed at evaluating the performance of latency estimation using different fMRI techniques, with two event‐related experiments at 3T. Experiment I evaluated latency variations within the visual cortex and their relationship with contrast‐to‐noise ratios (CNRs) for GRE, spin echo (SE), and diffusion‐weighted SE (DWSE). Experiment II used delayed visual stimuli between two hemifields (delay time = 0, 250, and 500 ms, respectively) to assess the temporal resolving power of three protocols: GRE_TR1000, GRE_TR500, and SE_TR1000. The results of experiment I showed the earliest latency with DWSE, followed by SE, and then GRE. Latency variations decreased as CNR increased. However, similar variations were found between GRE and SE, when the latter had lower CNR. In experiment II, measured stimulus delays from all conditions were significantly correlated with preset stimulus delays. Inter‐subject variation in the measured delay was found to be greatest with GRE_TR1000, followed by GRE_TR500, and the least with SE_TR1000. Conclusively, blood oxygenation level‐dependent responses obtained from GRE exhibit greater CNR but no compromised latency variations in the visual cortex. SE is potentially capable of improving the performance of latency estimation, especially for group analysis. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 215–221, 2013     

Upper disparity limit after LASIK

We evaluate the effect of the emmetropization technique LASIK (laser-assisted in situ keratomileusis) on stereoscopic vision. For this, we used a mirror stereoscope to measure the upper disparity limit D(max) before (with best correction) and after LASIK for 30 patients. The results show that the upper disparity limit declines from 41.1 min of arc on average to 31.3 min of arc after LASIK, being significant in 83% of the patients. This deterioration is significantly correlated with an increase in the postsurgical interocular differences in higher-order aberrations, corneal asphericity, and presurgical anisometropia. New ablation algorithms should minimize interocular differences in order to improve binocular visual performance.     

Exploring human brain neuronal currents with phase MRI

Purpose: Brain activity‐associated neuronal currents produce weak transient magnetic fields that would affect both magnitude and phase of the local MRI signal, but these very small signal changes are not reliably detectable with conventional fMRI methodologies. A recent simulation study, using a realistic model specifically for human cerebral cortex, indicates that the phase signal change induced by spontaneous activity may reach a detectable level (up to 0.2°) in favorable conditions. This study aimed to investigate neuronal current‐induced signal changes in human visual cortex with phase MRI. Materials and Methods: Six healthy subjects participated in a phase fMRI study using a temporally well‐controlled visual stimulation paradigm with a known neuronal firing pattern in visual cortex. The precise timing of the paradigm provides a means of detecting and testing the neuronal current‐induced phase signal changes, and placing a series of acquisition windows to fully cover the entire response duration enables a thorough detection of any detectable phase signal changes induced by the stimulus‐evoked neuronal currents. Results: The presented phase MRI method demonstrated to be reliable, and the improved phase measure has achieved a sensitivity level of 0.2° for detecting any significant phase signal changes under a practical length of fMRI session. The test found no sign of any significant neuronal current‐induced phase signal changes in any subject and study. Conclusions: Under the experimental condition, the upper limit of the neuronal current‐induced phase signal changes was found to be less than 0.2° in the human visual cortex, consistent with the model prediction.