Multisensory contributions to the perception of motion

The ability to process motion is crucial for coherent perception and action. While the majority of studies have focused on the unimodal factors that influence motion perception (see, for example, the other chapters in this Special Issue), some researchers have also investigated the extent to which information presented in one sensory modality can affect the perception of motion for stimuli presented in another modality. Although early studies often gave rise to mixed results, the development of increasingly sophisticated psychophysical paradigms are now enabling researchers to determine the spatiotemporal constraints on multisensory interactions in the perception of motion. Recent findings indicate that these interactions stand over-and-above the multisensory interactions documented previously for static stimuli, such as the oft-cited 'ventriloquism' effect. Neuroimaging and neuropsychological studies are also beginning to elucidate the network of neural structures responsible for the processing of motion information in the different sensory modalities, an important first step that will ultimately lead to the determination of the neural substrates underlying these multisensory contributions to motion perception.     

Reasons for poor cataract surgery uptake - a qualitative study in rural South Africa

OBJECTIVES: To understand the reasons for poor cataract surgery uptake in people with blindness or severe visual impairment in rural South Africa. METHODS: A qualitative analysis of detailed, domiciliary interviews with a community-based random sample of elderly Zulus who were blind or severely visually impaired as a result of operable cataract, who had previously been invited for surgery but had failed to attend. RESULTS: Fear of surgery and a fatalistic attitude to the inevitability and irreversibility of blindness in old age were the main reasons for failure to attend for surgery. There was a lower level of disability and perceived need than had been assumed for people with such poor visual acuity. Non-surgical western style health care for systemic illness was common but few patients had sought any form of assistance for their poor vision. Issues of cost and accessibility were relatively unimportant. CONCLUSION: Provision of affordable and accessible cataract surgery for the blind and severely visually impaired members of a community does not guarantee that it will be taken up. Other barriers to surgery may be revealed when practical issues such as cost and accessibility are addressed. Perceptions of visual disability among subjects with cataract may differ from simple objective clinical standards.     

白内障患者双眼先后手术后视功能调查量表结果的比较

目的:通过视功能调查量表比较第一眼和第二眼白内障超声乳化吸除联合人工晶状体植入术后患者视功能的变化。方法:先后作双眼白内障超声乳化吸除联合人工晶状体植入术的患者47人,分别在第一眼和第二眼手术前和手术后1周作眼科检查并完成视功能调查量表。结果:第一眼手术后视功能及各指标得分均高于术前;第二眼术后视功能及周边视野和立体觉的得分高于第二眼手术前,与视力有关的日常生活限制和感觉适应的得分在第二眼术后无明显变化。结论:第一眼和第二眼术后视功能均得到提高,第二眼手术后以周边视野和立体觉的改善为主。     

晚期青光眼患者视野检查的可靠性分析

目的本文探讨晚期青光眼与早中期青光眼患者视野检测的可靠性是否存在显著性差异。方法以2002年4月至2003年12月随诊于我科的临床确诊为青光眼的患者作为研究对象,应用OCTOPUS101型视野计中G2/TOP程序对双眼进行视野检测。以每位患者有一次以上视野检查经历及裸眼视力≥0.5,瞳孔直径大于2.5mm作为入选标准。共157只眼(90位患者)入选;年龄25岁到79岁,男性29人、女性61人。结果以平均缺损指数(MD,meandefect)分组:MD≥15dB为晚期青光眼组;MD<15dB为早中期青光眼组。MD≥15dB组RF值35.73±3.69,显著高于MD<15dB组5.14±0.73(P<0.01);根据RF值进行分组:RF>15%为RF异常组;RF≤15%为RF正常组,RF异常组的MD值8.64±1.08显著高于RF正常组4.38±0.38(P<0.01)。晚期青光眼组患者假阴性率远高于早中期青光眼组。结论晚期青光眼患者视野检查的可靠性因子(RF)与早中期患者相比有显著差异,在视野损伤严重的患者,高RF值并不一定代表患者视野检查的可靠性差,相反,当青光眼损伤到一定程度,RF值随之增大,可能与损伤程度有关。高RF值来源于高的假阴性率,青光眼的加重导致假阴性率的增高。     

垂体瘤卒中手术后患者视力视野改变的临床研究

目的探讨垂体瘤卒中手术后视力、视野的改善情况。方法对38例垂体瘤卒中患者均采用手术治疗,其中25例采取急诊手术治疗,其余13例采取择期手术治疗。结果急诊手术治疗术后视力、视野完全恢复正常14例(56.00%),部分恢复9例(36.00%),无变化2例(8.00%);择期手术治疗术后视力、视野完全恢复正常2例(15.38%),部分恢复6例(46.15%),无变化3例(20.00%),恶化2例(15.38%)。结论垂体瘤卒中发病后手术时间越早,术后病人视力及视野恢复越好。     

磁共振成像、视诱发电位和视野检查在视神经炎的临床应用

目的 探讨MRI、视诱发电位(VEP)和视野(Vision Field，VF)在视神经炎中的临床应用价值。方法 临床诊断为视神经炎者60例分别行MRI、VEP和视野检查，每例所有检查均在一周内完成，并将检查结果进行统计学处理和分析。结果 MRI阳性率最高(96．67％)，其次是视野和VEP(86．96％和75．58％)。同时发现MRI具有定位和一定的鉴别诊断作用。结论 VEP和VF结合MRI检查，三者相辅相成，将有助于视神经炎更早、更准确地诊断和治疗。     

Spatial Orientation Adjustments in Children with Autism in Hong Kong

Abnormal spatial orientation and body postures in children with autism often interfere with visual abilities to attend tasks and social interactions. Twenty-four children diagnosed with autism from Kowloon, Hong Kong were assessed for spatial orientation and spatial management abilities. Positive changes in spatial orientation were evident when the children wore ambient prism lenses and included changes in posture from slanted to erect. Adjustments in spatial management were evident in improved ball catching ability, a task requiring visual tracking and eye-hand coordination. The findings suggest that alterations to the sensory systems may lead to behavioral change in some children.     

A study on contrast discrimination of CT images

We investigated the range of differences in CT values by which radiologists could distinguish among tissues. The contrast discrimination thresholds and contrast discrimination ratios were determined. The test pattern consisted of a square CT film (12 cm in width and 6 cm in length). The film had a circular reference field and a circular test field. Each field was 1 cm in diameter with the distance between the two center being 6.5 cm. The reference fields were set at 60 or 100 H. U.. The test fields were changed and compared with the reference. The window width (WW) and the window level (WL) were set at 400 and 50 H. U. or 250 and 60 H. U.. The contrast dincrimination thresholds for ten observers ranged from 5.9 to 19.3 H. U., and the contrast discrimination ratios were from 11.5 to 21.3%. The effect of WW on contrast discrimination was analyzed for various WWs ranging from 200 to 1000 H. U.. Changes in WW produced no significant difference under the conditions of this investigation.     

Post-suppression vestibulo-ocular reflex in man: visual and non-visual mechanisms

Summary The vestibulo-ocular reflex (VOR) was intermittently suppressed by fixating a head-fixed target (light on: 9 s; darkness: 2 s) during whole-body (60–100 deg/s peak; 0.01–0.17 Hz) sinusoidal and triangular oscillation about the vertical axis for about 2 min. Eye movements associated with intervals of darkness at different phases of body oscillation were stimulus-locked averaged, thereby estimating the post-suppression VOR. The gain ({eye velocity}/ {head velocity}) of the post-suppression VOR was generally 26–50% of the normal gain in maintained darkness. During sinusoidal body oscillation, the phase lead of the post-suppression VOR equalled or, at low frequencies, appeared to exceed the normal lead in maintained darkness. When the light was permanently extinguished after 2 min of intermittent suppression, an initially reduced VOR rapidly (e.g., 0.4 s) appeared and required 6–30 s to build up to normal again. These observations indicated that visual suppression of the VOR dissipated in darkness with rapid and slow components. During 0.17 Hz, 60 deg/s sinusoidal oscillation, the rapid (perhaps visual) component was responsible for 1/3, and the slow (perhaps non-visual) component for 2/3, of all suppressive effects.     

On-axis and off-axis viewing of images on CRT displays and LCDs: observer performance and vision model predictions

RATIONALE AND OBJECTIVES: Although cathode-ray tube (CRT) displays typically are used for softcopy display of radiographs in the digital reading environment, liquid crystal displays (LCDs) currently are being used as an alternative. LCDs have many desirable viewing properties compared with a CRT, but significant image degradation can occur with off-axis viewing. This study compares observer performance and predictions from a human visual system model for on-axis and off-axis viewing for CRT displays versus LCDs. MATERIALS AND METHODS: A set of mammograms with different lesion contrasts (n = 400) were shown to six radiologists on CRT and LCD monitors, once on-axis and once off-axis. Observer performance was measured by using receiver operating characteristic techniques. Performance was correlated with results of a human vision model designed to predict observer performance (just noticeable difference [JND]metrix model). Two approaches were used to generate model metrics; a paired discrimination and channelized model observer approach. RESULTS: The performance of human observers indicated that on-axis viewing with the LCD was better than with the CRT, but off-axis viewing was significantly better with the CRT than LCD (F = 8.8175; P < .0001). The paired discrimination model correctly predicted on-axis, but not off-axis, results. The channelized model observer correctly predicted both on- and off-axis results. CONCLUSION: Off-axis viewing of radiographic images on an LCD monitor degrades human observer performance significantly compared with a CRT display. Care should be taken in the clinic to avoid off-axis viewing during diagnostic interpretation.