Contrast Sensitivity Characteristics Research Articles

Characteristics of Visual Contrast Sensitivity and Ocular Microtremor in Schizophrenia

Background: schizophrenia is a severe mental illness characterized not only by cognitive but also sensory impairments, including the visual system. Research suggests impairments in contrast processing in schizophrenia, but evidence regarding the nature of these impairments is inconsistent. The theory of tremor modulation signal connects contrast sensitivity with the parameters of ocular microtremor – high-frequency and low-amplitude micromovements that are controlled by neurons of the nuclei of the brain stem. The parameters of ocular microtremor in psychopathology, in particular in schizophrenia, have not been described in the scientific literature.The aim of the study was to study the characteristics of contrast sensitivity and microtremor of the eyes of patients with schizophrenia.Patients and methods: to register contrast sensitivity, the method of computer visocontrastometry was used. Gabor elements were presented with spatial frequencies of 0.4, 1.0, 3.0, and 10 cycles/deg. Eye microtremor was recorded using a non-contact high-speed video recording method using an original optical system. The study involved 30 patients diagnosed as paranoid schizophrenia and 30 people without psychopathology and neurological diseases.Results: the contrast sensitivity of patients was reduced in the region of medium and high spatial frequencies compared with conditionally healthy controls, which may be associated with the chronic course of the disease. Ocular microtremor in the patient group was characterized by a lower frequency and a higher amplitude compared to the control group.Conclusions: contrast sensitivity and ocular microtremor are considered as potential markers for determining the functional state in schizophrenia, which requires further research and accumulation of experimental data.

Cognitive Functioning and Visual System Characteristics in Schizophrenia: A Cross-Sectional Study

Background: increasing interest in visual disturbances in schizophrenia is connected with the fact that they are a potential biomarker for objectification of a mental condition. The nature of the relationship between visual disturbances and higher-level cognitive functions in schizophrenia remains understudied.The aim of the study was to investigate differences in visual information processing between individuals with paranoid schizophrenia and healthy individuals, and to analyze the relationship between visual system characteristics with clinical and cognitive factors.Patients and methods: thirty-three patients with the paranoid form of schizophrenia and 19 healthy subjects were included in the cross-sectional study. Cognitive impairment was assessed using a battery of BACS tests, and the severity of the mental state was assessed using the PANSS scale. Contrast sensitivity characteristics were measured by computer visocontrastometry.Results: the study found that the visual system of persons with schizophrenia is characterized by hypersensitivity in the high and midrange, but decreased sensitivity in the low-frequency range. Decreased sensitivity in the low-frequency range was associated with better cognitive functioning and less pronounced productive symptoms. Medium frequencies at the trend level correlated with the digit sequencing tests, assessing working memory, and verbal fluency, reflecting speed of information processing.Conclusions: our findings expand information on the character of the relationship between contrast sensitivity and cognitive function. The results of study will provide the basis for further research on the development of more effective non-medicinal methods to improve cognitive functioning.

Improved SSIM IQA of contrast distortion based on the contrast sensitivity characteristics of HVS

Currently, the structural similarity index metric (SSIM) is recognised generally and applied widely in image quality assessment (IQA). However, using SSIM to evaluate contrast-distorted images from TID2013 and CSIQ databases is low effective. In this study, the authors improve SSIM for contrast-distorted images by combining it with the contrast sensitivity characteristics of human visual system (HVS). In the improved method, first, they combine the visual characteristics to propose a model that HVS perceives the real image. Then, this model is used to eliminate the visual redundancy of real images. Afterwards, the perceived images are evaluated using SSIM. Furthermore, 241 contrast-distorted images from TID2013 and CSIQ databases were used in experiments. The results have shown that in comparison with SSIM scores, the scores obtained by the improved SSIM are more consistent with the subjective assessment scores. Moreover, the Pearson linear correlation coefficient and Spearman rank order correlation coefficient between subjective and objective scores are averagely improved by 12.83 and 22.78%, respectively. In addition, the assessment accuracy of the improved SSIM is better than that of five commonly used IQA metrics. Also, it has an excellent generalisation performance. These results show that the assessment performance of the improved SSIM is effectively enhanced.

基于人眼对比敏感视觉特性的彩色图像盲水印算法

基于人眼对比敏感视觉特性的彩色图像盲水印算法

A novel color image compression algorithm using the human visual contrast sensitivity characteristics

In order to achieve higher image compression ratio and improve visual perception of the decompressed image, a novel color image compression scheme based on the contrast sensitivity characteristics of the human visual system (HVS) is proposed. In the proposed scheme, firstly the image is converted into the YCrCb color space and divided into sub-blocks. Afterwards, the discrete cosine transform is carried out for each sub-block, and three quantization matrices are built to quantize the frequency spectrum coefficients of the images by combining the contrast sensitivity characteristics of HVS. The Huffman algorithm is used to encode the quantized data. The inverse process involves decompression and matching to reconstruct the decompressed color image. And simulations are carried out for two color images. The results show that the average structural similarity index measurement (SSIM) and peak signal to noise ratio (PSNR) under the approximate compression ratio could be increased by 2.78% and 5.48%, respectively, compared with the joint photographic experts group (JPEG) compression. The results indicate that the proposed compression algorithm in the text is feasible and effective to achieve higher compression ratio under ensuring the encoding and image quality, which can fully meet the needs of storage and transmission of color images in daily life.

Stereo chromatic contrast sensitivity model to blue-yellow gratings.

As a fundamental metric of human visual system (HVS), contrast sensitivity function (CSF) is typically measured by sinusoidal gratings at the detection of thresholds for psychophysically defined cardinal channels: luminance, red-green, and blue-yellow. Chromatic CSF, which is a quick and valid index to measure human visual performance and various retinal diseases in two-dimensional (2D) space, can not be directly applied into the measurement of human stereo visual performance. And no existing perception model considers the influence of chromatic CSF of inclined planes on depth perception in three-dimensional (3D) space. The main aim of this research is to extend traditional chromatic contrast sensitivity characteristics to 3D space and build a model applicable in 3D space, for example, strengthening stereo quality of 3D images. This research also attempts to build a vision model or method to check human visual characteristics of stereo blindness. In this paper, CRT screen was clockwise and anti-clockwise rotated respectively to form the inclined planes. Four inclined planes were selected to investigate human chromatic vision in 3D space and contrast threshold of each inclined plane was measured with 18 observers. Stimuli were isoluminant blue-yellow sinusoidal gratings. Horizontal spatial frequencies ranged from 0.05 to 5 c/d. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. According to the relationship between spatial frequency of inclined plane and horizontal spatial frequency, the chromatic contrast sensitivity characteristics in 3D space have been modeled based on the experimental data. The results show that the proposed model can well predicted human chromatic contrast sensitivity characteristics in 3D space.

结合人眼对比度敏感视觉特性的视频质量客观评价

结合人眼对比度敏感视觉特性的视频质量客观评价

基于人眼对比度敏感视觉特性的彩色图像压缩技术

According to the measurement process of the human visual contrast sensitivity characteristics and characteristics of Discrete Cosine Transform of the image,a color image compression technology program is proposed based on human visual characteristics.In the program,the color image is converted and described in CLELAB color space at first,and each of the three components of the color image is processed by Discrete Cosine Transform.Secondly,the transform domain coefficients are quantified according to the contrast sensitivity function model of human vision and coefficient's characteristics of Discrete Cosine Transform.The color image is encoded using Huffman algorithm.Lastly compressed images are decompressed using the inverse process,and the color images are matched after decompression.The simulation results show that PSNR can reach 37 dB or more when the compression ratio is 98.355 5∶1,and the human eye can not distinguish the differences between the source image and decompressed image,and the coding efficiency can reach more than 0.74,redundancy in 0.26 below,which shows that the color image compression technology solutions proposed can achieve a higher compression ratio under the premise of ensuring the encoding quality and image quality,and is a feasible and effective solution for color image compression technology.

一种利用人眼视觉特性的数字图像水印技术

Based on the contrast sensitivity characteristics of human vision system and image features,a method was proposed to calculate the just noticeable difference thresholds of different frequencies of spectrum image.The thresholds was utilized to determine the watermark embedding and extraction.The watermarking scheme was designed,validated by experiment,and tested by attack,the results show that the peak signal noise ratio are all larger than 30 dB when JPEG compression quality factor is bigger than 30%,which indicates that the watermarks are well concealed.Normalized correlation value could still get to 0.653 9 under the case of compression quality factor of 20%,and the extracted watermarks could still clearly be seen intuitively.

基于人眼对比度敏感视觉特性的图像质量评价方法

Combined the traditional gray image quality assessment method described by the mean square error and peak signal to noise ratio and color differences to describe color image difference,a color image quality assessment method described by the color difference MSE and color difference PSNR statistical parameters based on human vision system is proposed,which is validated by the experiments.Experimental results match the subjective image quality assessment provided by LIVE subjective image library,University of Texas at Austin very much,which shows that the method not only effectively reflects the difference among the local location or points from the statistical significance,and at the same time,which improves the consistency between the objective evaluation and subjective evaluation because the statistical method takes into account the human vision system characteristics.

Contrast sensitivity characteristics of school-aged myopic subjects

Contrast sensitivity characteristics of school-aged myopic subjects

Theoretical reproduction of perceptual responses to drifting image using a spatio-temporal human vision model with a multiple-channel structure

A human vision model with a multiple-channel structure that can quantitatively simulate spatio-temporal perceptual responses to flickering sinusoidal waves as well as still images has already been proposed. This model was mathematically formulated as an adaptive focus adjustable feedback system based on two essential properties of the human vision system: the interdependent relationship between a retinal image's blur and a visual field size; and the spatio-temporal response characteristics of retinal ganglion cells. However, as the latter characteristics were actually formulated by utilizing spatio-temporal frequency characteristics experimentally measured using flickering sinusoidal waves, it is very important to confirm the model's applicability to images whose temporal change characteristics differ from flickering images. This paper discusses the model's applicability to drifting sinusoidal waves, which have a typical kind of temporal change characteristic except for flickering images. Consequently, it was clarified that the model's spatial frequency characteristics of contrast sensitivity and those of optimum drifting speed are in good agreement with experimental data. These results suggest that this model is also applicable to images with various kinds of temporal change characteristics other than flickering patterns. This provides the model's validity or generality. Moreover, the model was applied to the theoretical prediction of perceptual response characteristics of drifting square waves. How drifting square waves were perceived is also discussed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(2): 35–45, 1997

Theoretical reproduction of perceptual responses to drifting image using a spatio‐temporal human vision model with a multiple‐channel structure

A human vision model with a multiple-channel structure that can quantitatively simulate spatio-temporal perceptual responses to flickering sinusoidal waves as well as still images has already been proposed. This model was mathematically formulated as an adaptive focus adjustable feedback system based on two essential properties of the human vision system: the interdependent relationship between a retinal image's blur and a visual field size; and the spatio-temporal response characteristics of retinal ganglion cells. However, as the latter characteristics were actually formulated by utilizing spatio-temporal frequency characteristics experimentally measured using flickering sinusoidal waves, it is very important to confirm the model's applicability to images whose temporal change characteristics differ from flickering images. This paper discusses the model's applicability to drifting sinusoidal waves, which have a typical kind of temporal change characteristic except for flickering images. Consequently, it was clarified that the model's spatial frequency characteristics of contrast sensitivity and those of optimum drifting speed are in good agreement with experimental data. These results suggest that this model is also applicable to images with various kinds of temporal change characteristics other than flickering patterns. This provides the model's validity or generality. Moreover, the model was applied to the theoretical prediction of perceptual response characteristics of drifting square waves. How drifting square waves were perceived is also discussed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(2): 35–45, 1997

Ultrafast Computed Tomography for Infants and Children

Experience using ultrafast CT in the diagnostic evaluation of more than 50 infants and children indicates that this new technique is highly accurate and easily performed. Ultrafast CT offers several advantages compared to conventional CT. Scan times of either 0.05 or 0.1 seconds were sufficiently short to eliminate motion artifacts, even without patient sedation; sedation is a routine procedure for the conventional CT examination of most infants and small children and carries a finite risk. Procedure time appears to be shorter using ultrafast CT, 15 minutes or less, than with conventional CT. No control data using conventional CT are available for this patient population, but generally pediatric body CT studies are scheduled at hourly intervals at our medical center and are rarely completed in less than 30 minutes. Dynamic imaging alternatives for evaluation of the pediatric heart and airway include angiocardiography, digital subtraction studies, and fluoroscopy, which are limited by relatively high radiation exposure and by the inability to display all wall motions simultaneously due to their projectional rather than tomographic orientation. The potential for acquiring serial 0.05-second images of rapidly moving structures, including the heart, airway, and lungs, is unique to the ultrafast CT technique and facilitates the identification of functional abnormalities, including intracardiac shunts, valvular obstructions, tracheomalacia, and segmental bronchial obstruction. The relationships of mediastinal soft tissue structures and vessels are well defined by both ultrafast and conventional CT. In situations in which fine spatial resolution is pivotally important, the radiologist has the option with the C-100 scanner to select the 0.1-second scanning mode. This mode results in a higher radiation exposure per slice, approximately two-fold, and also uses an array of more closely spaced detectors, 864, to increase dose efficiency and spatial resolution. Although not generally required for our pediatric patients, one has the additional option of performing repeated 0.1-second images at any level, as many as ten exposures, totaling 1.0 seconds, to increase photon flux and increase resolution. Thus, the choice of scanning options can markedly influence both radiation dose, resolution, and contrast sensitivity characteristics.

A spatio-temporal model of ganglion cell receptive field in the cat retina

A spatio-temporal model of ganglion cell receptive fields is proposed on the basis of receptive field characteristics of cat retinal ganglion cells reported in our previous paper. The model consists of the linear and nonlinear mechanisms in the ganglion cell receptive field. The linear mechanism is assumed to be composed of antagonistic center and surround mechanisms. Then, by integrating these mechanisms we construct a spatio-temporal impulse response function of ganglion cell receptive field. Here we assume that spatio-temporal impulse response function may be factored into spatial and temporal terms. By Fouriertransforming the spatio-temporal impulse response function, we can obtain the spatio-temporal transfer function. Contrast sensitivity characteristics of X-and Y-cells in the cat retina may be explained by the transfer function.

Temporal sensitivity in amblyopia: An explanation of conflicting reports

Although the spatial characteristics of contrast sensitivity in amblyopia are well established, it is still not clear how temporal vision is affected. A wide range of spatial stimuli have been used to measure flicker sensitivity in amblyopia and we have considered the possibility that reported inconsistancies in results are due to a confounding of spatial and temporal stimulus parameters. To address this question we have measured contrast sensitivity from a sample of eight strabismic/anisometropic amblyopes using (1) stationary sinusoidal gratings, (2) uniform field flicker and (3) counterphased flickering gratings. In each case the contrast sensitivity deficits were predictably determined by the spatial properties of the stimulus (spot size or spatial frequency), and the spatial characteristics of the amblyopia. Results are nearly independent of the temporal properties of the stimulus. Specifically, when the stimulus is sufficiently large, or consists of low spatial frequencies, no temporal deficits are found. We conclude that conflicts between previous reports are attributable primarily to differences in spatial characteristics of the stimuli used.