Visual field inhomogeneous in brain-computer interfaces based on rapid serial visual presentation

Objective. Visual attention is not homogeneous across the visual field, while how to mine the effective EEG characteristics that are sensitive to the inhomogeneous of visual attention and further explore applications such as the performance of brain-computer interface (BCI) are still distressing explorative scientists. Approach. Images were encoded into a rapid serial visual presentation (RSVP) paradigm, and were presented in three visuospatial patterns (central, left/right, upper/lower) at the stimulation frequencies of 10Hz, 15Hz and 20Hz. The comparisons among different visual fields were conducted in the dimensions of subjective behavioral and EEG characteristics. Furthermore, the effective features (e.g. SSVEP, N2pc and P300) that sensitive to visual-field asymmetry were also explored. Results. The visual fields had significant influences on the performance of RSVP target detection, in which the performance of central was better than that of peripheral visual field, the performance of horizontal meridian was better than that of vertical meridian, the performance of left visual field was better than that of right visual field, and the performance of upper visual field was better than that of lower visual field. Furthermore, stimuli of different visual fields had significant effects on the spatial distributions of EEG, in which N2pc and P300 showed left-right asymmetry in occipital and frontal regions, respectively. In addition, the evidences of SSVEP characteristics indicated that there was obvious overlap of visual fields on the horizontal meridian, but not on the vertical meridian. Significance. The conclusions of this study provide insights into the relationship between visual field inhomogeneous and EEG characteristics. In addition, this study has the potential to achieve precise positioning of the target's spatial orientation in RSVP-BCIs.

Predictive value of OCT and MRI for postoperative visual recovery in patients with chiasmal compressive lesions

Purpose We aimed to investigate the predictive value of retinal thickness measured by optical coherence tomography (OCT) and mass biometrics measured using magnetic resonance image (MRI) for visual recovery after surgery for removal of a mass compressing the optic chiasm. Methods Consecutive patients who showed typical temporal visual field defect (VFD) with respect to the vertical meridian due to a chiasmal compressive mass and who underwent mass removal surgery were recruited. Ophthalmic examination was performed preoperatively and postoperatively. Retinal thickness was measured by the Cirrus OCT. The height and size of the mass and suprasellar extension (SSE) in both the sagittal and coronal planes were evaluated. Patients were divided into two groups based on the improvement in VFD (mean deviation [MD] change ≥ 5 dB: group R; others: group NR) and clinical characteristics were compared. Results Fifteen patients were included in the study. Eight (53.3%) patients were allocated into group R and others (7 patients, 46.7%) into group NR. Age, sex, initial visual acuity, initial MD was not different between the two groups. The retinal thicknesses were not different while tumor height, volume, and both sagittal and coronal SSE were significantly different between the two groups. (p = 0.029, 0.014, <0.001, and <0.001, respectively) All MRI parameters showed significant predictive value for the degree of MD recovery. Conclusion MRI showed better predictive value than OCT in predicting postoperative VFD recovery in patients with temporal VFDs due to chiasmal compressive disorder.

The influence of non-neural factors on BOLD signal magnitude

To what extent is the size of the blood-oxygen-level-dependent (BOLD) response influenced by factors other than neural activity? In a re-analysis of three neuroimaging datasets, we find large systematic inhomogeneities in the BOLD response magnitude in primary visual cortex (V1): stimulus-evoked BOLD responses, expressed in units of percent signal change, are up to 50% larger along the representation of the horizontal meridian than the vertical meridian. To assess whether this surprising effect can be interpreted as differences in local neural activity, we quantified several factors that potentially contribute to the size of the BOLD response. We find strong relationships between BOLD response magnitude and cortical thickness, cortical curvature, and the presence of large veins. These relationships are consistently found across subjects and suggest that variation in BOLD response magnitudes across cortical locations reflects, in part, differences in anatomy and vascularization. To compensate for these factors, we implement a regression-based correction method and show that after correction, BOLD responses become more homogeneous across V1. The correction reduces the horizontal/vertical difference by about half, indicating that some of the difference is likely not due to neural activity differences. Additionally, we find that while the cerebral sinuses overlap with the vertical meridian representation in V1, they do not explain the observed horizontal/vertical difference. We conclude that interpretation of variation in BOLD response magnitude across cortical locations should consider the influence of the potential confounding factors of cortical thickness, curvature, and vascularization.

Linking individual differences in human V1 to perception around the visual field

A central question in neuroscience is how the organization of cortical maps relates to perception, for which human primary visual cortex (V1) is an ideal model system. V1 nonuniformly samples the retinal image, with greater cortical magnification (surface area per degree of visual field) at the fovea than periphery, and at the horizontal than vertical meridian. Moreover, the size and organization of V1 differs greatly across individuals. Here, we used fMRI and psychophysics in the same individuals to quantify individual differences in V1 cortical magnification and perceptual contrast sensitivity at the four polar angle meridians. Across individuals, the overall size of V1 and localized cortical magnification both positively correlated with contrast sensitivity. Moreover, increases in cortical magnification and contrast sensitivity at the horizontal compared to the vertical meridian were strongly correlated. These data reveal a tight link between cortical anatomy and visual perception at the level of individual observer and stimulus location.

The Effect of Toric Intraocular Lens Implantation in Irregular Corneal Steep and Flat Meridian

Purpose. To evaluate the effect of toric intraocular lens implantation in cataract patients with irregular corneal steep and flat meridian. Methods. Data of 112 eyes of 78 patients who underwent toric intraocular lens implantation were analyzed retrospectively. Steep meridian deviations (not 180°) and steep and flat meridian deviations (not 90°) were classified as 0, 1–9, 10–19, 20–29, 30–39, and over 30°. Meridian deviation was measured with a sagittal map of a rotating Scheimpflug camera (Pentacam®: Oculus, Wetzlar, Germany) using PicPickTools (NGWIN, Seoul, Korea). Results. Residual astigmatism (D) of 0 (0.51 ± 0.13, 0.55 ± 0.15) and 1–9 (0.61 ± 0.16, 0.66 ± 0.19) groups were significantly lower than that of 10–19 (0.92 ± 0.24, 0.90 ± 0.28), 20–29 (0.10 ± 0.32, 1.01 ± 0.35), and over 30° groups (1.12 ± 0.37, 1.14 ± 0.40) both in steep meridian deviations and horizontal and vertical meridian deviations at 6 months ( P < 0.05 ). Postoperative mean UCVA (logMAR) of 0 (0.09 ± 0.04, 0.09 ± 0.05) (logMAR) and 1–9 (0.10 ± 0.04, 0.11 ± 0.08) groups was significantly improved compared to that of 10–19 (0.14 ± 0.05, 0.17 ± 0.10), 20–29 (0.18 ± 0.08, 0.21 ± 0.10), and over 30° groups (0.20 ± 0.09, 0.22 ± 0.11) both in steep meridian deviations and horizontal and vertical meridian deviations at 6 months ( P < 0.05 ). Conclusions. Correction of astigmatism with toric intraocular lens implantation is not accurate in corneas with steep meridian deviations and steep and flat meridian deviations of more than 10°. Therefore, care should be taken when we perform toric intraocular lens implantation in patients with irregular corneal meridian.

Presaccadic attention enhances contrast sensitivity, but not at the upper vertical meridian

Human visual performance is not only better at the fovea and decreases with eccentricity, but also has striking radial asymmetries around the visual field: At a fixed eccentricity, it is better along (1) the horizontal than vertical meridian and (2) the lower than upper vertical meridian. These asymmetries, known as performance fields, are pervasive -they emerge for many visual dimensions, regardless of head rotation, stimulus orientation or display luminance- and resilient -they are not alleviated by covert exogenous or endogenous attention, deployed in the absence of eye movements. Performance fields have been studied exclusively during eye fixation. However, a major driver of everyday attentional orienting is saccade preparation, during which visual attention automatically shifts to the future eye fixation. This presaccadic shift of attention is considered strong and compulsory, and relies on fundamentally different neural computations and substrates than covert attention. Given these differences, we investigated whether presaccadic attention can compensate for the ubiquitous performance asymmetries observed during eye fixation. Our data replicate polar performance asymmetries during fixation and document the same asymmetries during saccade preparation. Crucially, however, presaccadic attention enhanced contrast sensitivity at the horizontal and lower vertical meridian, but not at the upper vertical meridian. Thus, instead of attenuating polar performance asymmetries, presaccadic attention exacerbates them.

Cortical Magnification in Human Visual Cortex Parallels Task Performance around the Visual Field

Human vision has striking radial asymmetries, with performance on many tasks varying sharply with stimulus polar angle. Performance is generally better on the horizontal than vertical meridian, and on the lower than upper vertical meridian, and these asymmetries decrease gradually with deviation from the vertical meridian. Here we report cortical magnification at a fine angular resolution around the visual field. This precision enables comparisons between cortical magnification and behavior, between cortical magnification and retinal cell densities, and between cortical magnification in twin pairs. We show that cortical magnification in human primary visual cortex, measured in 163 subjects, varies substantially around the visual field, with a pattern similar to behavior. These radial asymmetries in cortex are larger than those found in the retina, and they are correlated between monozygotic twin pairs. These findings indicate a tight link between cortical topography and behavior, and suggest that visual field asymmetries are partly heritable.

The Correlations between Horizontal and Vertical Peripheral Refractions and Human Eye Shape Using Magnetic Resonance Imaging in Highly Myopic Eyes

The aim of this study was to determine the relationship between relative peripheral refraction and retinal shape by 2-D magnetic resonance imaging in high myopes. Thirty-five young adults aged 20 to 30 years participated in this study with 16 high myopes (spherical equivalent < −6.00 D) and 19 emmetropes (+0.50 to −0.50 D). An open field autorefractor was used to measure refractions from the center out to 60° in the horizontal meridian and out to around 20° in the vertical meridian, with a step of 3 degrees. Axial length was measured by using A-scan ultrasonography. In addition, images of axial, sagittal, and tangential sections were obtained using 2-D magnetic resonance imaging. The highly myopic group had a significantly relative peripheral hyperopic refraction and showed a prolate ocular shape compared to the emmetropic group. The highly myopic group had relative peripheral hyperopic refraction and showed a prolate ocular form. Significant differences in the ratios of height/axial (1.01 ± 0.02 vs. 0.94 ± 0.03) and width/axial (0.99 ± 0.17 vs. 0.93 ± 0.04) were found from the MRI images between the emmetropic and the highly myopic eyes (p < 0.001). There was a negative correlation between the retina’s curvature and relative peripheral refraction for both temporal (Pearson r = −0.459; p < 0.01) and nasal (Pearson r = −0.277; p = 0.011) retina. For the highly myopic eyes, the amount of peripheral hyperopic defocus is correlated to its ocular shape deformation. This could be the first study investigating the relationship between peripheral refraction and ocular dimension in high myopes, and it is hoped to provide useful knowledge of how the development of myopia changes human eye shape.

Crossed–uncrossed projections from primate retina are adapted to disparities of natural scenes

In mammals with frontal eyes, optic-nerve fibers from nasal retina project to the contralateral hemisphere of the brain, and fibers from temporal retina project ipsilaterally. The division between crossed and uncrossed projections occurs at or near the vertical meridian. If the division was precise, a problem would arise. Small objects near midline, but nearer or farther than current fixation, would produce signals that travel to opposite hemispheres, making the binocular disparity of those objects difficult to compute. However, in species that have been studied, the division is not precise. Rather, there are overlapping crossed and uncrossed projections such that some fibers from nasal retina project ipsilaterally as well as contralaterally and some from temporal retina project contralaterally as well as ipsilaterally. This increases the probability that signals from an object near vertical midline travel to the same hemisphere, thereby aiding disparity estimation. We investigated whether there is a deficit in binocular vision near the vertical meridian in humans and found no evidence for one. We also investigated the effectiveness of the observed decussation pattern, quantified from anatomical data in monkeys and humans. We used measurements of naturally occurring disparities in humans to determine disparity distributions across the visual field. We then used those distributions to calculate the probability of natural disparities transmitting to the same hemisphere, thereby aiding disparity computation. We found that the pattern of overlapping projections is quite effective. Thus, crossed and uncrossed projections from the retinas are well designed for aiding disparity estimation and stereopsis.