Parafoveal Visual Field Research Articles

An early effect of the parafoveal preview on post-saccadic processing of English words.

A key aspect of efficient visual processing is to use current and previous information to make predictions about what we will see next. In natural viewing, and when looking at words, there is typically an indication of forthcoming visual information from extrafoveal areas of the visual field before we make an eye movement to an object or word of interest. This "preview effect" has been studied for many years in the word reading literature and, more recently, in object perception. Here, we integrated methods from word recognition and object perception to investigate the timing of the preview on neural measures of word recognition. Through a combined use of EEG and eye-tracking, a group of multilingual participants took part in a gaze-contingent, single-shot saccade experiment in which words appeared in their parafoveal visual field. In valid preview trials, the same word was presented during the preview and after the saccade, while in the invalid condition, the saccade target was a number string that turned into a word during the saccade. As hypothesized, the valid preview greatly reduced the fixation-related evoked response. Interestingly, multivariate decoding analyses revealed much earlier preview effects than previously reported for words, and individual decoding performance correlated with participant reading scores. These results demonstrate that a parafoveal preview can influence relatively early aspects of post-saccadic word processing and help to resolve some discrepancies between the word and object literatures.

Topographic organization across foveal visual areas in macaques.

While the fovea on the retina covers only a small region of the visual field, a significant portion of the visual cortex is dedicated to processing information from the fovea being a critical center for object recognition, motion control, and visually guided attention. Despite its importance, prior functional imaging studies in awake monkeys often focused on the parafoveal visual field, potentially leading to inaccuracies in understanding the brain structure underlying function. In this study, our aim is to unveil the neuronal connectivity and topography in the foveal visual cortex in comparison to the parafoveal visual cortex. Using four different types of retrograde tracers, we selectively injected them into the striate cortex (V1) or V4, encompassing the regions between the fovea and parafovea. V1 and V4 exhibited intense mutual connectivity in the foveal visual field, in contrast to the parafoveal visual field, possibly due to the absence of V3 in the foveal visual field. While previous live brain imaging studies failed to reveal retinotopy in the foveal visual fields, our results indicate that the foveal visual fields have continuous topographic connectivity across V1 through V4, as well as the parafoveal visual fields. Although a simple extension of the retinotopic isoeccentricity maps from V1 to V4 has been suggested from previous fMRI studies, our study demonstrated that V3 and V4 possess gradually smaller topographic maps compared to V1 and V2. Feedback projections to foveal V1 primarily originate from the infragranular layers of foveal V2 and V4, while feedforward projections to foveal V4 arise from both supragranular and infragranular layers of foveal V1 and V2, consistent with previous findings in the parafoveal visual fields. This study provides valuable insights into the connectivity of the foveal visual cortex, which was ambiguous in previous imaging studies.

Early visual experience refines the retinotopic organization within and across visual cortical regions

Early visual areas are retinotopically organized in human and non-human primates. Population receptive field (pRF) size increases with eccentricity and from lower- to higher-level visual areas. Furthermore, the cortical magnification factor (CMF), a measure of how much cortical space is devoted to each degree of visual angle, is typically larger for foveal as opposed to peripheral regions of the visual field. Whether this fine-scale organization within and across visual areas depends on early visual experience has yet been unknown. Here, we employed 7T functional magnetic resonance imaging pRF mapping to assess the retinotopic organization of early visual regions (i.e., V1, V2, and V3) in eight sight recovery individuals with a history of congenital blindness until a maximum of 4 years of age. Compared with sighted controls, foveal pRF sizes in these individuals were larger, and pRF sizes did not show the typical increase with eccentricity and down the visual cortical processing stream (V1-V2-V3). Cortical magnification was overall diminished and decreased less from foveal to parafoveal visual field locations. Furthermore, cortical magnification correlated with visual acuity in sight recovery individuals. The results of this study suggest that early visual experience is essential for refining a presumably innate prototypical retinotopic organization in humans within and across visual areas, which seems to be crucial for acquiring full visual capabilities.

The effects of rehabilitative interventions on reading disorders caused by homonymous visual field defects: a meta-analysis focusing on improvement in reading speed.

Reading disorders caused by homonymous visual field defects (HVFDs) have a significant impact on a patient's quality of life. However, no review has been conducted to evaluate the available evidence on the effects of rehabilitative interventions on reading disorders caused by HVFDs. Thus, the aim of this study was to systematically evaluate the effects of rehabilitative interventions on reading disorders caused by HVFDs. We searched the MEDLINE/PubMed, Cochrane Library, ClinicalTrials.gov, CINAHL, and ScienceDirect databases for relevant articles. Relevant search terms were used to identify reports of randomized controlled trials or randomized crossover trials published between January 1990 and December 2021. Only studies that included reading-speed-related outcomes were analyzed. Risk of bias was assessed using the PEDro scale. Meta-analysis was conducted using a random-effects model, and standardized mean differences (SMD) and 95% confidence intervals (CIs) were calculated. Heterogeneity was assessed using the Ι2 statistic. Nine studies were included in the meta-analysis. The results showed that rehabilitative interventions significantly improved reading disorders caused by HVFDs (SMD = 0.30; 95% CI 0.08-0.51; P < 0.01; Ι2 = 0.0%). Subgroup analysis showed that reading training significantly improved reading disorders (SMD = 0.35; 95% CI 0.05-0.66; P = 0.02; Ι2 = 0.0%). Reading disorders caused by HVFDs can be improved through rehabilitation. In addition, reading training for the improvement of eye movement and fixation to compensate for foveal and parafoveal visual field defects may improve reading speed.

Comparison of pattern electroretinograms of glaucoma patients with parafoveal scotoma versus peripheral nasal step

Retinal ganglion cells are distributed disproportionately with retinal eccentricity. Pattern electroretinogram (PERG) stimuli resulted in reduced responses with more eccentric stimuli. Therefore, we investigated whether PERG amplitude is associated with the location of visual field (VF) defect in primary open-angle glaucoma. Data from Twenty-nine glaucoma patients with a parafoveal scotoma (PFS) within the central 10° of fixation, 23 glaucoma patients with a peripheral nasal step (PNS), and 27 normal control subjects were analyzed in this study. Electroretinograms (ERGs) were obtained using a commercial ERG stimulator (Neuro-ERG). The thickness of the ganglion cell-inner plexiform layer (GCIPL) was measured using spectral-domain optical coherence tomography. A lower N95 amplitude was observed in both PFS and PNS compared to the normal control (Both P < 0.001). The N95 amplitude of the PFS group was significantly lower than that of the PNS group (P = 0.034). Average GCIPL thickness correlated positively with N95 amplitude (r = 0.368, P = 0.002), but did not correlate significantly with global mean sensitivity (r = 0.228, P = 0.073) or mean deviation on 24-2 standard automated perimetry (r = 0.173, P = 0.176). In conclusion, parafoveal VF defects were associated with the lower PERG amplitude. Therefore, it is necessary to take into account the location of VF defects in evaluating PERGs of glaucoma patients.

Systemic Vascular Risk Factors for Multiple Retinal Nerve Fiber Layer Defects

Multiple retinal nerve fiber layer (RNFL) defects develop uncommonly, even though glaucomatous RNFL loss is typically observed as one RNFL defect in each quadrant. We investigated the risk factors associated with multiple RNFL defects to increase our understanding of the nature and pathogenesis of various RNFL defect patterns. Data from subjects with multiple RNFL defects (28 patients) and glaucoma patients without multiple RNFL defects (194 patients) were analyzed. The term “multiple RNFL defects” refers to three or more isolated defects separated by a comparatively normal area. Patients with multiple RNFL defects showed a higher prevalence of hypertension, end-stage renal disease, and cerebrovascular disease than those without multiple RNFL defects, both before and after propensity score matching for age and mean deviation (all P < 0.05). The number of patients with parafoveal visual field points depressed <5% on pattern deviation plots was higher in subjects with multiple RNFL defects than in those without multiple RNFL defects (P = 0.048). In conclusion, the presence of multiple RNFL defects had clinical relevance for systemic vascular risk factors and a higher risk of parafoveal scotoma. Clinicians should be aware of the possibility of concomitant systemic vascular disease when evaluating patients with multiple RNFL defects.

Choroidal Microvasculature Dropout Is Associated With Parafoveal Visual Field Defects in Glaucoma

To determine whether the frequency of parafoveal visual field (VF) damage differs according to the presence of choroidal microvasculature dropout (CMvD) in open-angle glaucoma (OAG) and to assess correlations between the angular circumference of CMvD and the severity of VF defects. Retrospective case-control study. This study enrolled 88 eyes of 88 consecutive OAG patients (44 with CMvD and 44 without CMvD matched for age [≤5 years], axial length [≤1mm], and the severity of VF loss [≤1 dB]). Angular circumference of CMvD was determined from choroidal layer images obtained from optical coherence tomography angiography. Demographic and ocular characteristics, including the presence of parafoveal VF defects and VF mean sensitivity (MS), were compared between OAG eyes with CMvD and those without. Logistic regression analyses were performed to derive the clinical factors associated with parafoveal VF defects. The relationships between CMvD angular circumference and global/regional VF defect severity were assessed. Parafoveal VF defects were observed in 96% (42/44) of eyes with CMvD but only in 39% (17/44) of eyes without CMvD. OAG eyes with CMvD showed significantly lower superior parafoveal VF MS compared to those without. A significant association was found between parafoveal VF defects and CMvD in OAG eyes, and CMvD angular circumference was significantly correlated with the severity of VF defects. The involvement of parafoveal VF defects was significantly associated with the presence of CMvD. Among eyes with CMvD, CMvD angular circumference had significant correlations with the severity of VF defects.

Cone Integrity in Glaucoma: An Adaptive-Optics Scanning Laser Ophthalmoscopy Study

To investigate photoreceptor changes in eyes with glaucoma. Cross-sectional study. The study included 35 eyes of 35 patients with primary open-angle glaucoma who had suffered parafoveal visual field loss at least 3 years previously, as well as 21 eyes of 21 normal subjects. Eyes with an axial length ≥26.0mm were excluded. All subjects underwent a full ophthalmologic examination, including spectral-domain optical coherence tomography (SDOCT) and prototype adaptive-optics scanning laser ophthalmoscopy (AO-SLO) imaging. As determined using AO-SLO, eyes with glaucoma did not differ significantly from normal eyes in terms of either cone density (26 468 ± 3392 cones/m2 vs 26 147 ± 2700 cones/m2, respectively; P= .77; measured 0.5mm from the foveal center) or cone spatial organization (ratio of hexagonal Voronoi domain: 43.7% ± 4.4% vs 44.3% ± 4.9%; P= .76; measured 0.5mm from the foveal center). Furthermore, SDOCT showed that the 2 groups did not differ significantly in terms of the photoreceptor-related layer thickness, and that the photoreceptor ellipsoid zone band was continuous in all normal and glaucoma eyes. In glaucoma eyes with vertically asymmetric severity, the more affected side did not significantly differ from the less affected side in terms of cone density, cone spatial organization, or photoreceptor-related layer thickness. In 8 eyes (22.9%) with glaucoma, dark, partition-like areas surrounded the cones on the AO-SLO. Both AO-SLO and SDOCT showed cone integrity in eyes with glaucoma, even in areas with visual field and nerve fiber loss. In AO-SLO, microcystic lesions in the inner nuclear layer may influence images of the cone mosaic.

Microstructure of the Optic Disc Pit in Open-Angle Glaucoma

To investigate the structural and clinical characteristics of the optic disc pit (ODP) in primary open-angle glaucoma (POAG) via enhanced depth imaging (EDI) spectral-domain optical coherence tomography (SD-OCT). Prospective, observational case series. Seventy POAG eyes clinically diagnosed with an ODP via stereo disc photography. Optic discs were scanned using EDI SD-OCT. Serial horizontal and vertical B-scan images covering the optic discs were obtained from each eye. The structural characteristics of the ODP were investigated via 3-dimensional images constructed from the serial B-scans, focusing on the presence of alterations in the contour of the lamina cribrosa (LC) or prelaminar tissue (PLT), in conjunction with associated clinical characteristics. The structural characteristics of the ODP and associated clinical characteristics. In the EDI SD-OCT images, the ODP was viewed as an isolated alteration of the LC (n = 14, 20.0%) or PLT (n = 16, 22.9%) or an alteration of both the LC and PLT (n = 40, 57.1%). Alterations of the LC were located at the mid-periphery near the LC insertion (n = 17) or far periphery adjacent to the LC insertion (n = 37), and the depth of alteration was deep (n = 23), involving nearly full-thickness LC, or shallow (n = 31), with partially visible LC at the base. Fifty-four eyes (77.1%) exhibited parafoveal visual field (VF) defect within 10 degrees of fixation, and in 98.1% of these eyes (53/54) it was spatially associated with the location of ODP. The parafoveal VF defect was more prevalent in eyes with LC alteration than those without (83.3% vs. 56.2%, P = 0.023) and in eyes with deep LC defect than those with shallow defect (95.7% vs. 74.2%, P = 0.036). Disc hemorrhage (32.4% vs. 0.0%, P = 0.008) and peripapillary retinoschisis (18.9 vs. 0.0%, P = 0.055) were more strongly associated with LC alterations located at the far periphery than at the mid-periphery. Enhanced depth imaging SD-OCT facilitated visualization of the varied structure of the ODP, which presented as alteration of the LC or PLT or both. The clinical significance of differing characteristics of ODP microstructure remains to be determined.

Glaucoma Diagnostic Ability of Ganglion Cell–Inner Plexiform Layer Thickness Differs According to the Location of Visual Field Loss

To determine whether the ganglion cell-inner plexiform layer (GCIPL) or circumpapillary retinal nerve fiber layer (cpRNFL) is better at distinguishing eyes with early glaucoma from normal eyes on the basis of the the initial location of the visual field (VF) damage. Retrospective, observational study. Eighty-four patients with early glaucoma and 43 normal subjects were enrolled. The patients with glaucoma were subdivided into 2 groups according to the location of VF damage: (1) an isolated parafoveal scotoma (PFS, N= 42) within 12 points of a central 10 degrees in 1 hemifield or (2) an isolated peripheral nasal step (PNS, N= 42) within the nasal periphery outside 10 degrees of fixation in 1 hemifield. All patients underwent macular and optic disc scanning using Cirrus high-definition optical coherence tomography (Carl Zeiss Meditec, Dublin, CA). The GCIPL and cpRNFL thicknesses were compared between groups. Areas under the receiver operating characteristic curves (AUCs) were calculated. Comparison of diagnostic ability using AUCs. The average and minimum GCIPL of the PFS group were significantly thinner than those of the PNS group, whereas there was no significant difference in the average retinal nerve fiber layer (RNFL) thickness between the 2 groups. The AUCs of the average (0.962) and minimum GCIPL (0.973) thicknesses did not differ from that of the average RNFL thickness (0.972) for discriminating glaucomatous changes between normal and all glaucoma eyes (P =0.566 and 0.974, respectively). In the PFS group, the AUCs of the average (0.988) and minimum GCIPL (0.999) thicknesses were greater than that of the average RNFL thickness (0.961, P =0.307 and 0.125, respectively). However, the AUCs of the average (0.936) and minimum GCIPL (0.947) thicknesses were lower than that of the average RNFL thickness (0.984) in the PNS group (P =0.032 and 0.069, respectively). The GCIPL parameters were more valuable than the cpRNFL parameters for detecting glaucoma in eyes with parafoveal VF loss, and the cpRNFL parameters were better than the GCIPL parameters for detecting glaucoma in eyes with peripheral VF loss. Clinicians should know that the diagnostic capability of macular GCIPL parameters depends largely on the location of the VF loss.

Processing temporal events simultaneously in healthy human adults and in hemi-neglect patients

Many theories have been advanced to explain how the brain incorporates time into its computations, in particular for the purpose of estimating the duration of an event. In the present study we examine with a new paradigm the ability to compare the duration of two visual stimuli in the parafoveal visual field, presented either sequentially or overlapping in time. We found that judging the duration of a pair of objects is more difficult when they overlap in time. Furthermore, all healthy participants presented a bias to over-estimate the duration of the second event (a negative time-order-error). We then presented the same task to eight left neglect patients with extinction (N-patients). Relative to the healthy participants, the patients displayed similar loss of sensitivity and increased bias in the time overlap condition. However, N-patients were particularly impaired when the first object was presented in their right visual field and the second one appeared on their left before the first one vanished. Rather than a simple engage/disengage disorder, these results highlight a specific problem with shifting attention to the impaired visual field. We discuss these findings in the light of contemporary models of time estimation.

Activation in left primary visual cortex representing parafoveal visual field during reading Japanese texts

Activation in the left primary visual cortex (V1) representing the parafoveal field during text reading has been interpreted as attentional modulation in the process of deciding saccadic target for reading ahead. Kanji words serve the main cue to decide the goal of saccades in Japanese. We aimed to determine the exact location of this modulation in the V1 and to determine whether the area of the modulation changes according to the location where the next Kanji word appears or it is fixed on a certain region in V1. Using functional magnetic resonance imaging, we determined the area in V1 representing each eccentricity on the horizontal meridian of the visual field for each participant. Then we investigated brain activation while they were reading two sets of Japanese texts that scrolled leftward as the participants. In set 1, the distance between the heads of adjacent Kanji words was about 3°. In set 2, the distance was about 5°. From the results of these experiments, we obtained activation amplitude of the area corresponding to each eccentricity. We recorded eye movements simultaneously with the acquisition of fMRI data. The maximum peak of the activation was found in the region representing about 4.5° of eccentricity on the horizontal meridian in the left V1 for each participant. The activation pattern did not essentially differ between the two text conditions, although the location of the saccades made for reading next section of the text corresponds to the head of the next Kanji word. The activation modulation during reading Japanese texts occurs in the parafoveal V1 of the left hemisphere. The attentional modulation did not change with the distance to the next goal of saccade but was fixed on the area representing about 4.5° of eccentricity.

Parafoveal vision impairments and their influence on reading performance and self-evaluated reading abilities

Patients with homonymous hemianopic field defects (HFD) after postchiasmatic cerebral brain injuries often complain about impairments in daily life activities, particularly problems in reading, and show considerable reductions of vision-related quality of life (QoL). This study aimed to assess the relation of "objective" reading performance and self-reported "subjective" reading abilities; it was further investigated whether parafoveal HFD characteristics have an impact on both parameters. In postchiasmatic-lesioned subjects with HFD (n = 43), "objective" reading performance was measured with Radner-Reading-Charts (reading speed, reading acuity). Vision-related QoL was assessed by the National-Eye-Institute-Visual-Function-Questionnaire (NEI-VFQ). Four reading-relevant NEI-VFQ items that assessed "subjective" reading abilities were separately analyzed. Macular sparing measures were derived from campimetry (+/-16 degrees vertical, +/-21.5 degrees horizontal); i.e., the vertical HFD border between +/-2 degrees and the proportion of intact parafoveal visual field within the "reading window". Since macular sparing may be a perimetric artefact, eye movements during campimetry were recorded in 26 subjects. Mean reading speed of the total sample (90.72 +/- 33.96 words per minute) was considerably reduced, as was the patients' vision-related QoL, which was revealed by diminished NEI-VFQ scores. Reading acuity was 0.12 +/- 0.13 LogRAD (0.81 +/- 0.26 according to the decimal system). There were significant but weak correlations between reading acuity and speed with all reading-relevant NEI-VFQ-items (r-range, reading acuity: -0.57 to -0.38, reading speed: 0.33 to 0.43) and 7/12 NEI-VFQ-subscales (r-range, reading acuity: -0.47 to -0.33, reading speed: 0.31 to 0.40). The intact parafoveal visual field correlated significantly with 2/4 reading-related NEI-VFQ-items and with 4/12 NEI-VFQ-subscales (r-range 0.31 to 0.52). Reading acuity and mean reading speed were both correlated with fixation accuracy during campimetry (r = -0.38 and 0.45). Correlations of spared areas between +2 degrees to -2 degrees and the relative and absolute defect HFD border with reading speed, but not reading acuity, tended to significance. Subjects deviated from the campimetric fixation mark in a SD-range of +/-5.2 degrees vertically and +/-6.5 degrees horizontally but eye movement ranges were not correlated with macular sparing measures. Patients with HFD showed severely reduced reading speed, which was reflected in subjectively diminished reading performance, and reduced reading-related QoL parameters. Larger areas of functionally intact parafoveal vision were associated with better reading performance. Although eye movements occurred during campimetry, these did not seem to constitute an artificially enlarged area of parafoveal intact vision.

視覚的注意がドリフト眼球運動に及ぼす影響の統計解析

Recent studies have demonstrated a close relationship between the frequency of microsaccades and covert attention shift. However, there are no arguments of attentional effect on drift movements during attentive or inattentive fixation. We examined whether visual attention has any influence on drift eye movements using statistical analysis of a time series of fixation eye movements. The results indicated that the power in the 3-4 Hz frequency range was enhanced when visual attention was dispersed over the parafoveal visual field. Furthermore, the amplitudes of the drift eye movements were reinforced immediately after the microsaccades, especially after square-wave jerks. These results suggest that microsaccades and drift eye movements are both controlled by higher order brain functions to acquire detailed visual information from the peripheral vision.

Two-Dimensional Mapping of the Central and Parafoveal Visual Field to Human Visual Cortex

Primate visual cortex contains a set of maps of visual space. These maps are fundamental to early visual processing, yet their form is not fully understood in humans. This is especially true for the central and most important part of the visual field--the fovea. We used functional magnetic resonance imaging (fMRI) to measure the mapping geometry of human V1 and V2 down to 0.5 degrees of eccentricity. By applying automated atlas fitting procedures to parametrize and average retinotopic measurements of eight brains, we provide a reference standard for the two-dimensional geometry of human early visual cortex of unprecedented precision and analyze this high-quality mean dataset with respect to the 2-dimensional cortical magnification morphometry. The analysis indicates that 1) area V1 has meridional isotropy in areal projection: equal areas of visual space are mapped to equal areas of cortex at any given eccentricity. 2) V1 has a systematic pattern of local anisotropies: cortical magnification varies between isopolar and isoeccentricity lines, and 3) the shape of V1 deviates systematically from the complex-log model, the fit of which is particularly poor close to the fovea. We therefore propose that human V1 be fitted by models based on an equal-area principle of its two-dimensional magnification. 4) V2 is elongated by a factor of 2 in eccentricity direction relative to V1 and has significantly more local anisotropy. We propose that V2 has systematic intrinsic curvature, but V1 is intrinsically flat.

Neurovisual rehabilitation: recent developments and future directions

Central visual1 and oculomotor2 disorders are present in some 20%-40% of patients in neurological rehabilitation centres.3 Gianutsos reported that 50% of the patients in a head trauma rehabilitation centre show visual system disorders not assessed before although most of the patients were chronic and had been treated in other hospitals previously.4 In a large sample of 314 patients with postchiasmatic visual field disorders from a rehabilitation department 70% had a parafoveal visual field sparing of 5° or less. Of these patients, 50%-70% subjectively reported and objectively showed chronic reading and visual exploration deficits.5 Furthermore, visual field disorders are associated with an adverse prognosis in outcome studies according to life table analysis6 and impair the success of vocational rehabilitation.4 7 Spatial-perceptual deficits may delay the rehabilitation progress in physiotherapy,8 9 lead to complications due to repeated accidents,10 and correlate highly with deficits in activities of daily living (dressing, transfers, or manoeuvring a wheelchair.11-16 In the presence of limited financial resources in health policy it might be argued that central visual disorders do not require treatment as they do not affect outcome adversely. Although nothing supports this opinion there is some evidence to the contrary. Cutting inpatient stroke rehabilitation to a maximum of 60 days (in Italy) led to a deterioration in neuropsychological and activities of daily living in patients with stroke, especially those with right hemispheric lesions.17 Hence, withdrawing neuropsychological treatment deteriorates functional performance and creates new costs. Whereas the systematic treatment of language, speech, and motor disorders is traditionally viewed as unequivocally necessary the possible influence of visual-sensory and oculomotor disorders on the patient's outcome is still neglected in neurorehabilitation. This review summarises therapeutic approaches for acquired central visual disorders. It is split into five parts. After an introduction …

Rehabilitation of homonymous hemianopsia

Homonymous hemianopia, most often caused by cerebral arterial infarction, represents for the patient a severe handicap, whereby beside bumping into persons and objects disturbance of reading and writing are predominant. In the beginning the patients often are not aware of the hemianopia (anosognosia) or even completely deny it (hemi-neglect). For rehabilitation of homonymous hemianopia different successful methods are at disposal. 1. Improvement of the patient's attention for the blind hemifield, 2. Enlargement of the saccadic search field. 3. Systematization of the search strategies, 4. Treatment of the hemianopic reading and writing disturbance, 5. Auxiliary optical measures. The rehabilitation of homonymous hemianopia with the described different methods is most successful and improves for the patient not only elementary and higher visual functions (visual exploration, reading and writing ability, parafoveal visual field, recognition of forms and colours), but may under favorable circumstances even restore partial or total working capacity.

人間の視覚・聴覚情報 マイクロサッカードの解析に基づく視覚的注意の定量的測定の試み

To evaluate the effects of visual attention (VA) on human involuntary miniature eye movements (MEM), we analyzed the microsaccades (MSC), which are components of MEM, under the following three experimental conditions : 1) VA was focused on the foveal object, 2) VA was dispersed in the parafoveal visual field, and 3) VA was focused on one of the parafoveal objects. The results showed that the VA was not focused on the foveal object, the frequency and amplitude of the MSC increased, and the scatter of fixation widened. The results from 2) and 3) showed that the frequency of the MSC was grater in 2) and the mean amplitude of the MSC was similar for both conditions. When VA is not focused, the MSC occur more frequently, and when VA is focused on the foveal object, the amplitude of the MSC reduces. These results suggest that MEM are influenced by VA, and MSC may be used as an indicator of the attentional state. It will be possible to establish whether VA is focused or not on the basis of the analysis of MEM characteristics.

Surface representation in the visual system

Perception of surface accompanies the impression that a certain area of the visual field is occupied by some quality, such as color, brightness and transparency. This does not mean, however, that information about surface quality must be obtained throughout the area. It has been shown in many situations that our visual system has ability to interpolate information obtained at the border of the surface and to perceive homogeneous surfaces. The most dramatic demonstration of this is the perceptual filling-in at the blind spot. In order to understand the neural representation of surface in the visual system, we conducted a series of experiments using macaque monkeys. First, we examined if neurons in the primary visual cortex (V1) respond when a homogeneous surface is presented on the receptive field. Neurons representing the parafoveal visual field were tested and it was found that about one third of neurons showed significant responses when the cell's receptive field was contained in a homogeneous surface. Then we examined neuron activities in the retinotopic representation of the blind spot in V1. Although there is no retinal input in the blind spot, a homogeneous surface is perceived within the blind spot as a result of filling-in. We tested whether neurons in this region were activated when a homogeneous surface was perceived in the blind spot as a result of filling-in. We found some neurons in V1 were activated by stimuli which lead to the filling-in. These results indicate that when a surface area is perceived, neurons are activated throughout the region in V1 topographically corresponding to the perceived surface and not restricted to the region representing the border of the surface.

Modeling Human Laser Eye Injury on Target Recognition Performance Using Simulated Scotomas

A laser accident patient's parafoveal visual field defect was modeled and his perform- ance on a tank recognition task was compared with that of a participant in the modeled scotoma condition and in two central scotoma conditions. The modeled parafoveal scotoma, and foveal and macular occluding scotomas were stabilized on the retina using a dual Purkinje Eye-Tracker and a multiplane digital image display. The simulated scotomas suppressed military target recognition functions in a manner consistent with previous studies. Neither central nor parafoveal scotomas were sufficient to reduce sensitivity to the patient's level. However, when the foveal and parafoveal scotoma functions were combined to account for the patient's macular damage, prediction for patient performance significantly improved. The data suggest that models of retinal damage from laser exposure must include not only visual field deficits but also deficits in high (visual acuity) and low spatial frequency visual function.