Interspecific differences in the visual system and scanning behavior of three forest passerines that form heterospecific flocks

Little is known as to how visual systems and visual behaviors vary within guilds in which species share the same micro-habitat types but use different foraging tactics. We studied different dimensions of the visual system and scanning behavior of Carolina chickadees, tufted titmice, and white-breasted nuthatches, which are tree foragers that form heterospecific flocks during the winter. All species had centro-temporally located foveae that project into the frontal part of the lateral visual field. Visual acuity was the highest in nuthatches, intermediate in titmice, and the lowest in chickadees. Chickadees and titmice had relatively wide binocular fields with a high degree of eye movement right above their short bills probably to converge their eyes while searching for food. Nuthatches had narrower binocular fields with a high degree of eye movement below their bills probably to orient the fovea toward the trunk while searching for food. Chickadees and titmice had higher scanning (e.g., head movement) rates than nuthatches probably due to their wider blind areas that limit visual coverage. The visual systems of these three species seem tuned to the visual challenges posed by the different foraging and scanning strategies that facilitate the partitioning of resources within this guild.     

Combined effects of chemical and visual information in eliciting antipredator behaviour in juvenile Atlantic salmon Salmo salar

Under natural conditions, both young-of-the-year (YOY; 0+ year) and parr (1+ year) Atlantic salmon Salmo salar exhibited strong antipredator behaviour ( e.g. increase in latency to resume foraging) following the exposure to damage-released chemical alarm cues relative to a stream water control. Subsequent exposure to a novel visual stimulus had contrasting results. Parr increased their reactive distance to the visual stimulus if they had been previously exposed to a chemical alarm cue, whereas YOY did not. On the other hand, both YOY and parr took significantly longer to resume foraging when exposed to a visual stimulus if they had been previously exposed to a chemical alarm cue than control groups. While YOY and parr differed in the type and intensity of antipredator responses to both chemical and visual stimuli, perhaps due to differential costs and benefits associated with age, both used the chemical and the visual information in a combined manner.     

The eyes of a patrolling butterfly: visual field and eye structure in the Orange Sulphur, Colias eurytheme (Lepidoptera, Pieridae)

Sensory information plays a critical role in determining an animal's behavior on both proximate and evolutionary timescales. Butterflies, like many other insects, use vision extensively over their lifetimes, and yet relatively little work has been published to date on their visual capabilities. We describe the visual system of a pierid butterfly, Colias eurytheme, with the ultimate goal of better understanding its role in shaping the behavior of this animal. We made several measurements: visual field dimensions, eye surface area, interommatidial angle (Deltaphi), facet diameter (D), and eye parameter (p). C. eurytheme had a large visual field and considerable regional variation in visual acuity, as inferred by Deltaphi and D. When compared to females, males had larger eye surface areas, smaller Deltaphi, and larger D in all regions except ventrally. Both sexes had proportionally large eye surface areas compared to other butterflies. Minimum p in males was small, indicating that some regions of their eyes may operate close to the diffraction limit. Finally, we found that both eye surface area and D scaled positively, but with negative allometry to body size. We discuss the relevance of these visual characteristics to the biology and behavior of C. eurytheme.     

Ocular Complications of Chloroquine Therapy

Ocular complications of long-term chloroquine therapy were observed in 18 of 45 patients so treated. This therapy was used in patients with rheumatoid arthritis, lupus erythematosus, sarcoidosis, discoid lupus and other chronic “collagen disease”. Thirteen patients had reversible corneal opacifications, and seven had irreversible retinal changes, with visual loss and visual field defects. Pathological evidence of chloroquine retinopathy was obtained in one patient. Physicians are therefore warned to use this drug only after careful consideration. If it is used, repeated ocular examinations should include assessment of visual acuity, visual fields on a tangent screen and fundus examination through a dilated pupil.     

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.     

The study of the latent periods of visual object differentiation by different significant characteristics

A total of 645 subjects between the ages of 5 and 24 years were examined by the original computer methods. Test subjects had to differentiate the visual stimuli by shape, color, size, and orientation. The latent periods of visual object differentiation had dissimilar significant characteristics and age dynamics. The obtained results are treated in the context of the concept of multichannel visual information processing.     

Mirrors as enrichment for captive chimpanzees (Pan troglodytes).

At many facilities, limitations of the physical environment have reduced the opportunity for captive chimpanzees to live in large, naturalistic social groups. Convex mirrors used to increase visual access of neighboring groups may improve the social environment. This was tested in a study of 28 chimpanzees (Pan troglodytes) group-housed in conventional indoor/outdoor runs. A total of 47.8 hours of behavioral observations were conducted and comparisons made across three conditions: no mirror present, a mirror present with visual access to neighboring conspecifics, or a mirror present with visual access to the neighbors' empty run. When the mirror gave subjects visual access to neighboring animals, facial expressions, sexual, and agonistic behaviors increased, whereas affiliative behavior decreased compared with when no mirror was present. When the mirror gave subjects visual access to a neighbors' empty run, facial expressions and sexual behavior increased compared with when no mirror was present. When the mirror gave subjects visual access to a neighbor's empty run, agonism decreased compared with when a mirror gave subjects visual access to neighboring animals. When subjects had visual access to neighbors, they used the mirror 30% of the total data points; while they had visual access to the neighbors' empty run, they looked during 24% of the total data points. Juveniles' use of the mirror increased over time while adults' use remained stable. Adult males used the mirror less than did the other subjects. These findings indicate that a mirror allowing visual access to neighboring conspecifics has potential as an enrichment device that affects social behavior.     

Traumatic optic neuropathy: a review of 61 patients

The outcome of traumatic optic neuropathy was evaluated following penetrating and blunt injuries to assess the effect of treatment options, including high-dose steroids, surgical intervention, and observation alone. Factors that affected improvement in visual acuity were identified and quantified. Sixty-one consecutive, nonrandomized patients presenting with visual loss after facial trauma between 1984 and 1996 were assessed for outcome. Pretreatment and posttreatment visual acuities were compared using a standard ophthalmologic conversion from the values of no light perception, light perception, hand motion, finger counting, and 20/800 down to 20/15 to a logarithm of the minimum angle of resolution (log MAR). The percentage of patients showing visual improvement and the degree of improvement were calculated for each patient group and treatment method. Measurements of visual acuity are in log MAR units +/- standard error of the mean.Patients who sustained penetrating facial trauma (n = 21) had worse outcomes than patients with blunt trauma (n = 40). Improvement in visual acuity after treatment was seen in 19 percent of patients with penetrating trauma compared with 45 percent of patients with blunt trauma (p < 0.05). Furthermore, patients with penetrating trauma improved less than those with blunt trauma, with a mean improvement of 0.4 +/- 0.23 log MAR compared with 1.1 +/- 0.24 in blunt-trauma patients (p = 0.03). The patients with blunt trauma underwent further study. There was no significant difference in improvement of visual acuity in patients treated with surgical versus nonsurgical methods; however, 83 percent of patients without orbital fractures had improvement compared with 38 percent of patients with orbital fractures (p < 0.05). The mean improvement in patients without orbital fractures was 1.8 +/- 0.65 log MAR compared with 0.95 +/- 0.26 in patients with orbital fractures (p = 0.1). Twenty-seven percent of patients who had no light perception on presentation experienced improvement in visual acuity after treatment compared with 100 percent of patients who had light perception on admission (p < 0.05). The mean improvement in patients who were initially without light perception was 0.85 +/- 0.29 log MAR compared with 1.77 +/- 0.35 in patients who had light perception (p < 0.05). There were no significant differences in improvement of visual acuity when analyzing the effect of patient age and timing of surgery. Patients who sustain penetrating trauma have a worse prognosis than those with blunt trauma. The presence of no light perception and an orbital fracture are poor prognostic factors in visual loss following blunt facial trauma. It seems that clinical judgment on indication and timing of surgery, and not absolute criteria, should be used in the management of traumatic optic neuropathy.     

Lateralized visual behavior in bottlenose dolphins (Tursiops truncatus) performing audio-visual tasks: the right visual field advantage

Analyzing cerebral asymmetries in various species helps in understanding brain organization. The left and right sides of the brain (lateralization) are involved in different cognitive and sensory functions. This study focuses on dolphin visual lateralization as expressed by spontaneous eye preference when performing a complex cognitive task; we examine lateralization when processing different visual stimuli displayed on an underwater touch-screen (two-dimensional figures, three-dimensional figures and dolphin/human video sequences). Three female bottlenose dolphins (Tursiops truncatus) were submitted to a 2-, 3- or 4-, choice visual/auditory discrimination problem, without any food reward: the subjects had to correctly match visual and acoustic stimuli together. In order to visualize and to touch the underwater target, the dolphins had to come close to the touch-screen and to position themselves using monocular vision (left or right eye) and/or binocular naso-ventral vision. The results showed an ability to associate simple visual forms and auditory information using an underwater touch-screen. Moreover, the subjects showed a spontaneous tendency to use monocular vision. Contrary to previous findings, our results did not clearly demonstrate right eye preference in spontaneous choice. However, the individuals' scores of correct answers were correlated with right eye vision, demonstrating the advantage of this visual field in visual information processing and suggesting a left hemispheric dominance. We also demonstrated that the nature of the presented visual stimulus does not seem to have any influence on the animals' monocular vision choice.     

Migraine-Like Visual Auras Among Traumatized Cambodians with PTSD: Fear of Ghost Attack and Other Disasters

This article profiles visual auras among traumatized Cambodian refugees attending a psychiatric clinic. Thirty-six percent (54/150) had experienced an aura in the previous 4 weeks, almost always phosphenes (48% [26/54]) or a scintillating scotoma (74% [40/54]). Aura and PTSD were highly associated: patients with visual aura in the last month had greater PTSD severity, 3.6 (SD = 1.8) versus 1.9 (SD = 1.6), t = 10.2 (df = 85), p < 0.001, and patients with PTSD had a higher rate of visual aura in the last month, 69% (22/32) versus 13% (7/55), odds ratio 15.1 (5.1–44.9), p < 0.001. Patients often had a visual aura triggered by rising up to the upright from a lying or sitting position, i.e., orthostasis, with the most common sequence being an aura triggered upon orthostasis during a migraine, experienced by 60% of those with aura. The visual aura was often catastrophically interpreted: as the dangerous assault of a supernatural being, most commonly the ghost of someone who died in the Pol Pot period. Aura often triggered flashback. Illustrative cases are provided. The article suggests the existence of local biocultural ontologies of trauma as evinced by the centrality of visual auras among Cambodian refugees.     

Aerial visual acuity in harbor seals (<Emphasis Type="Italic">Phoca vitulina</Emphasis>) as a function of luminance

In this study, we measured aerial visual acuity in harbor seals. As a first approach to the hypothesis that harbor seals can obtain acute aerial visual acuity mediated by the interaction of the vertical slit-shaped pupil and the corneal flattening although refractive measurements had revealed aerial myopia, visual acuity was tested as a function of luminance and pupil dilation. We analyzed aerial visual acuity (minimal resolvable stripe width) in three harbor seals in a two-alternative-forced-choice discrimination experiment. Our results further support the hypothesis that harbor seals possess an aerial visual acuity comparable to the acuity in clear waters if the vertical slit pupil does not exceed the zone of corneal flattening in bright light. When the pupil dilates with decreasing luminance, visual acuity decreases which might be due to deflected light from the stronger curved peripheral cornea.     

Vestibular capture of the perceived distance of passive linear self motion

The relative role of visual and vestibular cues in determining the perceived distance of passive, linear self motion were assessed. Seventeen subjects were given cues to constant acceleration motion: either optic flow, physical motion in the dark or combinations of visual and physical motion. Subjects indicated when they perceived they had traversed a distance that had been previously indicated either visually or physically. The perceived distance of motion evoked by optic flow was accurate relative to a visual target but was perceptually equivalent to a shorter physical motion. The perceived distance of physical motion in the dark was accurate relative to a previously presented physical motion but was perceptually equivalent to a much longer visually presented distance. The perceived distance of self-motion when both visual and physical cues were present was perceptually equivalent to the physical motion experienced and not the simultaneous visual motion even when the target was presented visually. We describe this dominance of the physical cues in determining the perceived distance of self motion as "vestibular capture".     

准分子激光治疗近视眼

本文对准分子激光PRK治疗近视眼息者503例的早期临床结果进行分析,近视范围为－2．0至－15．0D,根据术前屈光度不同分为三组,术后随访三个月．结果证实准分子激光是一种安全、有效、预测性较好的治疗近视眼方法．全部病人提高了裸眼视力,绝大部分保持了最佳矫正视力,且没有产生危及视力的并发症．     

Neurodevelopmental outcome in children with periventricular leukomalacia

The purpose of this study was to question the correlation of different grades of periventricular leukomalacia (PVL) and subsequent neurodevelopmental outcome. In a prospective study we followed 52 preterm infants. Infants were divided into three groups according to their cranial ultrasound findings of PVL (De Vries classification). Seventeen children had PVL 1, 20 children had PVL 2, and 15 children had PVL 3. All 15 (100%) children with PVL 3 developed cerebral palsy with additional visual perceptual dysfunctions and epilepsy. Children with PVL 1 had high frequency of mild neuromotoric delay and visual impairment. PVL 2 and 3 have great predictive value for subsequent severe neurodevelopmental disorder which refers to cerebral palsy, different cognitive deficits, vision impairment and epilepsy. We have determined that due to high frequency of visual impairment and epilepsy we need to include neurophysiologic examinations very early in children with PVL lesions.     

Brief daily periods of binocular vision prevent deprivation-induced acuity loss

The role of experience in the development of the central visual pathways has been explored in the past through examination of the consequences of imposed periods of continuously abnormal or biased visual input. The massive changes in the visual cortex (area 17) induced by selected early visual experience, especially monocular deprivation (MD) or experience (ME) where patterned visual input is provided to just one eye, are accompanied by profound and long-standing visual deficits. Although the use of exclusively abnormal experience permits identification of those aspects of the visual cortex and of visual function that can be influenced by visual experience during development, this approach may provide a distorted view of the nature of the role of visual experience because of the absence of any normal visual input. In this study a different approach was used whereby animals were provided daily with separate periods of normal (i.e., binocular exposure) and abnormal (monocular exposure) visual experience. We show that 2 hr of daily normal concordant binocular experience (BE) can outweigh or protect against much longer periods of monocular deprivation (MD) and permit the development of normal visual acuities in the two eyes. This result is not what would be expected if all visual input had equal influence on visual development.     

Screening for impaired visual acuity in middle age in general practice.

Screening for impaired distant visual acuity was one component of a controlled trial of multiphasic screening in middle age carried out in two general practices. The prevalence of impaired visual acuity (6/18 or worse in the better eye) at the initial screening in 1967 was 9.6% overall, ranging from 5.9% in people aged 40-49 years to 16.3% in those aged over 60. The question "Do you have difficulty seeing distant objects?" had a low sensitivity and high specificity, rendering it unsatisfactory for use in mass population screening for visual impairment. The prevalences of impaired visual acuity in the screening and control groups at the survey in 1972 showed no significant differences in any age group. Mass screening for defects of visual acuity in the course of a multiphasic examination is thus unlikely to reduce the prevalence of impaired distant visual acuity in the community.     

Tuning of photoreceptor spectral sensitivity in fireflies (Coleoptera: Lampyridae)

Sexual communication between male and female fireflies involves the visual detection of species-specific bioluminescent signals. Firefly species vary spectrally in both their emitted light and in the sensitivity of the eye, depending on the time when each is active. Tuning of spectral sensitivity in three firefly species that occupy different photic niches was investigated using light and electron microscopy, microspectrophotometry, and intracellular recording to characterize the location and spectral absorption of the screening pigments that filter incoming light, the visual pigments that receive this filtered light, and the visual spectral sensitivity. Twilight-active species had similar pink screening pigments, but the visual pigment of Photinus pyralis peaked near 545 nm, while that of P. scintillans had a λ_max near 557 nm. The night-active Photuris versicolor had a yellow screening pigment that was uniquely localized, while its visual pigment was similar to that of P. pyralis. These results show that both screening and visual pigments vary among species. Modeling of spectral tuning indicates that the combination of screening and visual pigments found in the retina of each species provides the best possible match of sensitivity to bioluminescent emission. This combination also produced model sensitivity spectra that closely resemble sensitivities measured either with electroretinographic or intracellular techniques. Vision in both species of Photinus appears to be evolutionarily tuned for maximum discrimination of conspecific signals from spectrally broader backgrounds. Ph. versicolor, on the other hand, appears to have a visual system that offers a compromise between maximum sensitivity to, and maximum discrimination of, their signals. Accepted: 29 September 1999     

Behavioral specialization in developing sciaenids and its relationship to morphology and habitat

Behavioral development of three species of marine sciaenid fish larvae was examined and related to their sensory morphology and habitat. Anti-predator behavior of the larvae was examined under different experimental conditions to isolate the roles of vision and mechanoreception. Spotted seatrout larvae maintained high levels of responsiveness even without visual cues but performed very poorly without mechanoreception. Loss of visual cues had no impact on the distance at which seatrout responded to the stimulus. Atlantic croaker generally performed best when vision was available. This species had low responsiveness without visual stimuli, and had smaller reactive distances when unable to use vision. Red drum were the most flexible in their use of sensory systems. For almost the entire larva period, responsiveness of red drum was equally high regardless of which sensory system was not available. In addition, reactive distances were unaffected when either visual or mechanoreceptive stimuli were eliminated. Thus, seatrout and croaker are sensory specialists, and red drum are sensory generalists. This is corroborated by previous studies on the sensory morphology of these species which showed that seatrout had more mechanosensory specialization, croaker had more visual specialization, and red drum were intermediate, with some enhancement of both systems. Behavioral data are interpreted in terms of habitat usage of the three species. Seatrout have the most restricted distribution over seagrass beds, croaker have a somewhat more flexible distribution, encompassing more open water habitats, and red drum have the most flexible range of habitats, using both vegetated and unvegetated portions of the estuary. These results indicate that even closely related species can exhibit different behaviors in order to better exploit the habitats in which they occur.     

Utility of visual evoked potentials using hemifield stimulation and several check sizes in the evaluation of suspected multiple sclerosis

One hundred and eleven patients with suspected multiple sclerosis (64 possible, 47 probable) and 16 with a definite diagnosis of MS were evaluated with pattern-reversal visual evoked potentials (VEPs), employing monocular full-field checks subtending 7′, 14′ and 28′ of visual angle, and right and left hemifield 28′ checks. Thirty-seven patients (29%) had a completely normal study. Sixty-six patients (52%) had abnormal responses to full-field 28′ checks, and in 13 (10%) of these, additional abnormalities were found in one or more of the other test conditions, which indicated the presence of an additional site of dysfunction in the visual pathway. Twenty-four patients (19%) with ‘normal’ full-field 28′ response had abnormalities in one or more of the other test conditions; these included prolonged latency to small size (7′ and 14′) full-field checks, abnormal responses in homonymous hemifields, and abnormal responses limited to a hemifield of one eye. Thus, the use of several check sizes and hemifield stimulation not only increases the sensitivity of VEPs in the evaluation of patients with suspected demyelinating disease, but enhances the capability of the VEP to demonstrate more than one area of visual system impairment.     

An Instrument for Biofeedback Applied to Vision

One hundred and ten patients (179 eyes) with reduced visual acuity caused by different ocular disorders underwent visual rehabilitation with an instrument for biofeedback: improved biofeedback integrated system (Ibis). One hundred and fourteen eyes had age-related macular degeneration, 39 eyes had myopic macular degeneration, and 26 eyes were affected by different ocular disorders. A placebo training was developed on 34 patients (47 eyes). Thirty-three eyes had age-related macular degeneration and 15 eyes had myopic macular degeneration. Visual acuity was found to be improved in 130/179 eyes (72.62%). Mean visual acuity was 0.24 before training and 0.36 at the last follow-up. A review of the literature and possible mechanisms are discussed.