Impact of binocular vision impairments on reading skills in first-year schoolchildren with high visual acuity

The aim of this study was to investigate the state of binocular vision in first-year schoolchildren with high binocular visual acuity. The results have shown that only 5.1% of these children had normal binocular vision, whereas 25.7% of them had moderate impairments, and 67.9% had severe plus moderate impairments in binocular vision. Significant intergroup differences between schoolchildren with learning difficulties in reading and children with normal reading have been detected in the mean indicators for the distance of near-point of convergence (p < 0.001) and the visual behavior symptoms that confirmed binocular dysfunctions (p < 0.002).     

Orientation selectivity of visual cortical neurons at different stimulus intensities in cats

Orientation selectivity of 24 neurons in area 17 of the visual cortex at different intensities of test bars of light, flashing against a constant light background in the center of the receptive field, was investigated in acute experiments on immobilized cats. Five neurons were invariant in orientation tuning to stimulus intensity (contrast): Although the magnitude of the response and acuteness of orientation selectivity were modified, preferential orientation was unchanged. More than half of the cells studied (13) were classed as noninvariant, for their preferential orientation was significantly shifted by 22–90° with a change in contrast. Small shifts of the peak of orientation selectivity, not statistically significant, were observed for the other neurons. Invariant neurons, unlike noninvariant, were characterized by preferential horizontal and vertical orientation, a lower frequency of spontaneous and evoked discharges, and the more frequent presence of receptive fields of simple type. The mechanisms of the change of orientation selectivity during contrast variation and also the different use of the two types of cells in orientation detection operations are discussed.     

Form perception and visual acuity in a chimpanzee

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.     

Wavelength dependence of visual acuity in goldfish

Visual acuity was measured in a two-choice training experiment with food reward. Four goldfish were trained to select a homogeneously illuminated testfield when a high-contrast grating (transparancy) was shown for comparison at the second testfield. Measurements were performed for white and monochromatic testfield illuminations in the light adapted state. Fourteen wavelengths between 404 nm and 683 nm were tested. For each wavelength (and white light) the testfield intensity was determined for which spatial resolution was highest. Between 446 nm and 683 nm maximal values of 2.0 cycles/deg (corresponding to a visual acuity of 15' of arc) were found. At 404 nm and in the ultraviolet resolution was lower (0.6 and ~0.25–0.35 cycles/deg, respectively). Cone and small ganglion cell densities may equally account for visual acuity. The action spectrum of maximal visual acuity is very similar to the spectral sensitivity function representing recognition of "colour". Measurements under reduced room illumination and after treatment with Ethambutol further indicate that the detection of high contrast gratings is processed by the same "channel" as colour vision. A similar separate and parallel processing of "colour" and "form" on the one hand, and "brightness" and "motion" on the other hand was found in humans.     

Objective measurements of visual acuity by visual evoked potentials

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.74 and a logarithmic dependence were obtained between spatial resolution measured by electrophysiological and psychophysical methods. The proposed methods of objective measurement of visual resolution has a high effectiveness, does not depend on specificity of individual EEG and domination of different channels in the visual system. Therefore it is possible to determinate objectively the visual acuity in humans independently of their responses.     

Comparative visual acuity of coleoid cephalopods

The pelagic realm of the ocean is characterized by extremelyclear water and a lack of surfaces. Adaptations to the visualecology of this environment include transparency, fluorescence,bioluminescence, and deep red or black pigmentation. While thesignals that pelagic organisms send are increasingly well-understood,the optical capabilities of their viewers, especially for predatorswith camera-like vision such as fish and squid, are almost unknown.Aquatic camera-like vision is characterized by a spherical lensfocusing an image on the retina. Here, we measured the resolvingpower of the lenses of eight species of pelagic cephalopodsto obtain an approximation of their visual capabilities. Wedid this by focusing a standard resolution target through dissectedlenses and calculating their modulation transfer functions.The modulation transfer function (MTF) is the single most completeexpression of the resolving capabilities of a lens. Since theoptical and retinal capabilities of an eye are generally well-matched,we considered our measurements of cephalopod lens MTF to bea good proxy for their visual capabilities in vivo. In general,squid have optical capabilities comparable to other organismsgenerally assumed to have good vision, such as fish and birds.Surprisingly, the optical capability of the eye of Vampyroteuthisinfernalis rivals that of humans.     

Orientation and direction selectivity of synaptic inputs in visual cortical neurons: a diversity of combinations produces spike tuning

This intracellular study investigates synaptic mechanisms of orientation and direction selectivity in cat area 17. Visually evoked inhibition was analyzed in 88 cells by detecting spike suppression, hyperpolarization, and reduction of trial-to-trial variability of membrane potential. In 25 of these cells, inhibition visibility was enhanced by depolarization and spike inactivation and by direct measurement of synaptic conductances. We conclude that excitatory and inhibitory inputs share the tuning preference of spiking output in 60% of cases, whereas inhibition is tuned to a different orientation in 40% of cases. For this latter type of cells, conductance measurements showed that excitation shared either the preference of the spiking output or that of the inhibition. This diversity of input combinations may reflect inhomogeneities in functional intracortical connectivity regulated by correlation-based activity-dependent processes.     

Orientation acuity estimated with simultaneous and successive procedures.

Orientation discrimination thresholds for medium contrast sinewave grating stimuli were estimated by a forced-choice procedure for the two principal, and the two main oblique axes. The results obtained for simultaneous presentation with a centre/surround stimulus arrangement are compared with the threshold estimates obtained when the two stimuli to be discriminated do not overlap in time. We find that orientation acuity depends on the temporal relationship of the discriminanda. Estimates of orientation threshold with simultaneous presentation are lower on all axes tested than those obtained with successive presentation; the greatest difference in orientation acuity was found at obliques. The data support the hypothesis that the meridional anisotropy in orientation discrimination that is found with conventional, two-interval forced-choice methods is not entirely attributable to anatomical and physiological changes at the level of the striate cortex.     

The relation between visual acuity and brightness discrimination

1. Visual acuity depends on the brightness contrast between test object and background; and conversely, brightness discrimination depends on the target size. Both functions vary with the brightness of the background. Measurements with rectangular targets of length-width ratio 2 were made over a range of sizes, contrasts, and brightnesses sufficient to determine the relations among these three variables. The rectangles were from 2' to 50' wide; the contrast fraction, DeltaI/I, ranged from 0.01 to 40; the background brightness varied from 0.0001 to 2500 millilamberts. 2. When DeltaI/I or visual acuity is plotted as a function of brightness the data do, in general, follow Hecht's equation. The departure from a simple photochemical theory which the larger targets show is probably due to changes in the functional retinal mosaic with changing brightness. 3. In general also, the relation between visual acuity and brightness, at selected contrasts, fits Hecht's derivation. At low contrasts, as the brightness is reduced a point is reached at which the test object becomes invisible at any size. 4. No simple relation emerges from the data relating visual acuity to contrast, at set levels of illumination. Over only a very short range are visual acuity and contrast directly related. At high contrasts, visual acuity reaches a maximum, whereas at low visual acuity, DeltaI/I reaches a minimum which cannot be passed regardless of size. 5. The shape of the curves relating DeltaI/I to brightness is not significantly altered by changing the exposure time. There is some evidence to show that a 3 second exposure of the target is equivalent to two looks of 0.2 second each. 6. In all these studies the thresholds were determined by a frequency of seeing method, and the data have been considered in terms of a quantum theory of threshold seeing. It was found that a threshold response involves between four and eight independent critical events, which are largely independent of size, brightness, and criterion of seeing.     

Similarity of visual selectivity among clonally related neurons in visual cortex

Neurons in rodent visual cortex are organized in a salt-and-pepper fashion for orientation selectivity, but it is still unknown how this functional architecture develops. A recent study reported that the progeny of single cortical progenitor cells are preferentially connected in the postnatal cortex. If these neurons acquire similar selectivity through their connections, a salt-and-pepper organization may be generated, because neurons derived from different progenitors are intermingled in rodents. Here we investigated whether clonally related cells have similar preferred orientation by using a transgenic mouse, which labels all the progeny of single cortical progenitor cells. We found that preferred orientations of clonally related cells are similar to each other, suggesting that cell lineage is involved in the development of response selectivity of neurons in the cortex. However, not all clonally related cells share response selectivity, suggesting that cell lineage is not the only determinant of response selectivity.     

大熊猫视力的定量化

有大量的研究提出,大熊猫具有发达的嗅觉和听觉系统但是视力很差。 虽然有些关于大熊猫视力和色觉方面的研究,但是至今我们对大熊猫的具体视力值方面的内容知之甚少。为了定量化大熊猫的视力值,我们观察并记录了8只圈养大熊猫（雌:雄=4:4）对于移动不同水平黑白相间条纹宽度的纸片的行为反应。我们发现,在测量距离为50 cm的情况下,大熊猫能够区分大约为0.46mm宽的黑白相间条纹。这个研究结果为大熊猫视网膜结构的解剖学研究提供了行为学支持,也为今后研究大熊猫的通讯和认知提供一定的参考。