Human Visual Response Research Articles

Eye Cataract Simulation Using Polymer Dispersed Liquid Crystal Scattering Obstacles

Polymer dispersed liquid crystals with electrically induced variations of light scattering extent similar to that of transparent PLZT ceramics are used for simulation of different development stages of eye cataract. Wavelength dependencies of scattering are determined in the visible spectral range, and human visual response looking through the scattering obstacle to the onset of various spatial frequency stimuli is determined psychophysically and electrophysiologically in order to find correlation between the scattering extent, visual acuity and visual evoked potential VEP chromatic characteristics.

Analysis on imaging features of mammography in computer radiography and investigation on gray scale transform and energy subtraction

In this dissertation, a novel transform method based on human visual response features for gray scale mammographic imaging in computer radiography (CR) is presented. The parameters for imaging quality on CR imaging for mammography were investigated experimentally. In addition, methods for image energy subtraction and a novel method of image registration for mammography of CR imaging are presented. Because the images are viewed and investigated by humans, the method of displaying differences in gray scale images is more convenient if the gray scale differences are displayed in a manner commensurate with human visual response principles. Through transformation of image gray scale with this method, the contrast of the image will be enhanced and the capability for humans to extract the useful information from the image will be increased. Tumors and microcalcifications are displayed in a form for humans to view more simply after transforming the image. The method is theoretically and experimentally investigated. Through measurement of the parameters of a geometrically blurred image, MTF, DQE, and ROC on CR imaging, and also comparison with the imaging quality of screen–film systems, the results indicate that CR imaging qualities in DQE and ROC are better than those of screen–film systems. In geometric blur of the image and MTF, the differences in image quality between CR and the screen–film system are very small. The results suggest that the CR system can replace the screen–film system for mammography imaging. In addition, the results show that the optimal imaging energy for CR mammography is about 24 kV. This condition indicates that the imaging energy of the CR system is lower than that of the screen–film system and, therefore, the x‐ray dose to the patient for mammography with the CR system is lower than that with the screen–film system. Based on the difference of penetrability of x ray with different wavelength, and the fact that the part of the x‐ray beam will pass through the image plate in the procedure of CR imaging, the method of subtraction of the two images which were taken in the same time with one exposure can increase the diagnostic information. Image registration for mammography with CR imaging is usually ignored because the two images are taken in one exposure time. This dissertation investigated the necessity of image registration for image energy subtraction in CR mammography imaging. A novel method for image registration that can reduce the computing time is established, based on the features of CR imaging for mammography.

A color coding method for radiographic images

Abstract A color scale was designed with an approach that combined both human visual response to color and physical properties of color. The design was initiated with a subjective evaluation of a 16 step color scale running from dark blue via magenta, orange to light yellow. The CIELUV chromaticity diagram was employed to verify the subjectively generated scale and to ensure that the differences in hue between the 16 steps was as equal as possible. The brightness of each step was adjusted to fit the function of the so-called L ∗ , which represents the response of the human visual system to luminance. Preliminary results using a computer generated radiograph indicate improved perception in color-coded than in black-and-white radiographs.

Evaluating the 1931 CIE color‐matching functions

AbstractThe use of colorimetry within industry has grown extensively in the last few decades. Central to many of today's instruments is the CIE system, established in 1931. Many have questioned the validity of the assumptions made by Wright1 and Guild,2 some suggesting that the 1931 color‐matching functions are not the best representation of the human visual system's cone responses. A computational analysis was performed using metameric data to evaluate the CIE 1931 color‐matching functions as compared to with other responsivity functions. The underlying assumption was that an optimal set of responsivity functions would yield minimal color‐difference error between pairs of visually matched metamers. The difference of average color differences found in the six chosen sets of responsivity functions was small. The CIE 1931 2° color‐matching functions on average yielded the largest color difference, 4.56 ΔE. The best performance came from the CIE 1964 10° color‐matching functions, which yielded an average color difference of 4.02 ΔE. An optimization was then performed to derive a new set of color‐matching functions that were visually matched using metameric pairs of spectral data. If all pairs were to be optimized to globally minimize the average color difference, it is expected that this would produce an optimal set of responsivity functions. The optimum solution was to use a weighted combination of each set of responsivity functions. The optimized set, called the Shaw and Fairchild responsivity functions, was able to reduce the average color difference to 3.92 ΔE. In the final part of this study a computer‐based simulation of the color differences between the sets of responsivity functions was built. This simulation allowed a user to load a spectral radiance or a spectral reflectance data file and display the tristimulus match predicted by each of the seven sets of responsivity functions. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 316–329, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10077

Foveated video quality assessment

Most image and video compression algorithms that have been proposed to improve picture quality relative to compression efficiency have either been designed based on objective criteria such as signal-to-noise-ratio (SNR) or have been evaluated, post-design, against competing methods using an objective sample measure. However, existing quantitative design criteria and numerical measurements of image and video quality both fail to adequately capture those attributes deemed important by the human visual system, except, perhaps, at very low error rates. We present a framework for assessing the quality of and determining the efficiency of foveated and compressed images and video streams. Image foveation is a process of nonuniform sampling that accords with the acquisition of visual information at the human retina. Foveated image/video compression algorithms seek to exploit this reduction of sensed information by nonuniformly reducing the resolution of the visual data. We develop unique algorithms for assessing the quality of foveated image/video data using a model of human visual response. We demonstrate these concepts on foveated, compressed video streams using modified (foveated) versions of H.263 that are standard-compliant. We rind that quality vs. compression is enhanced considerably by the foveation approach.

Rate dependence of human visual cortical response due to brief stimulation: an event-related fMRI study

The human brain response to a wide range of visual stimulus rates presented over a prolonged time period has been investigated by various neuroimaging techniques. However, to date, no imaging study has been performed to study the dynamic human brain response to various stimulus rates when presented in a short time. This report describes activation in the human brain due to brief visual stimulus presentation (1 s) for stimulus rates varying from 1 to 20 Hz using event-related functional MRI (fMRI). Our results show that the amplitude of the fMRI response increases with the stimulus frequency and plateaus at 6 Hz. This finding differs slightly from the results of previous blocked task paradigm experiments (with a longer time of stimulus presentation), in which the response peaks at approximately 8 Hz and then decreases. Our results are in close agreement with previously published psychophysical studies, suggesting that the fMRI signal in this experiment is indicative of cortical activity related to visual processing.

An objective measurement tool for MPEG video quality

A two-stage objective measurement model for MPEG-coded video is proposed. The first stage weights the coded video distortion according to the human visual system's response. It computes the frame-by-frame perceptual impairment in the decoded picture with respect to a reference picture; this includes low-pass spatial filtering, a Sobel operation to derive masking coefficients, and spatial masking on the raw error between reference and compressed pictures. The second stage, a cognitive emulator, provides a simulation of human high-level processing of visual information. This includes the very low temporal response of human viewers to image quality changes, and asymmetric behaviour in respect of picture quality changes from bad to good, and vice versa. With this model, we have been able to mimic quite accurately the temporally varying subjective picture quality of video sequences as recorded by the ITU-R SSCQE method.

Human visual responses in the absence of the geniculo-calcarine projection

Human visual responses in the absence of the geniculo-calcarine projection

Higher-Order Motion Perception in Human Visual Cortex: Evidence from fMRI

fMRI was used to investigate human visual cortex responses to higher-order motion stimuli. Acquisition was on a Siemens 1.5 T scanner (T2*, gradient-recalled EPI, TR 3000 ms, TE 84 ms, flip angle 90°, 2 mm × 2 mm voxels, 256 mm FOV, 10 4-mm slices, 54 acquisitions per run). The measured volume included occipital and posterior parietal cortex. T1 scouts and, in some subjects, high resolution T1 volume images were also acquired. Visual stimuli were gamma-corrected movies (480 × 480 pixels), presented by a PowerMac via an LCD projector, shown through the rear of the scanner onto an adjustable mirror fixed above the subject's eyes. Three types of stimuli were used: (1) first-order motion, (2) second-order motion (both radial sine waves on random-dot backgrounds), (3) structure-from-motion consisting of two rotating circular patches (5 deg diameter) within which dots moved in a constant (centripetal) direction, superimposed on randomly moving dots. Three interleaved comparisons were made: stimulus vs blank, first-order vs second-order, and random motion vs structure-from-motion (27 s each phase, 3 repeats). Analysis was based on a correlation coefficient method, after head-motion correction. Initial correlation was with the stimulus profile vector, then with an average BOLD response vector. Voxels with a correlation >0.5 (p<0.0003) were accepted as significant. In all subjects (seven- teen normals), all stimuli evoked bilateral activity in V1/V2 (BA17/18), and in extrastriate area V5/MT (BA37/19). Bilateral activation was also found in areas V3/V3a (BA19) and BA7. A more pronounced activation of area MST/V5a (BA37/39) was found in response to the structure-from-motion stimulus, compared with random motion.[Supported by: Wellcome Trust, Schilling Foundation.]

Improving the visual quality of JPEG-encoded images via companding

A companding procedure designed to improve the visual quality of monochrome images encoded with the baseline Joint Photographic Experts Group (JPEG) image compression algorithm is described. The companding procedure consists of two pointwise nonlinearities applied to the image, one before and one after the JPEG encoding. In a series of two-alternative forced-choice experiments designed to measure human visual threshold response to these images, it was determined that the average bitrate at the justnoticeable- difference (JND) point for the companded images is less than that for the uncompanded images. In a suprathreshold experiment, the subjects selected the companded images as being less distorted than the uncompanded images in more than 80% of the trials, for image bitrates ranging from 0.4 to 1.0 bpp.

A video-input device that displays high-luminance, high-resolution color images.

We describe the design and performance of a bright, full-color, video-input display monitor that can produce image luminances as high as 50,000 cd/m2 for images 15 x 10 deg in size. We have constructed this device by rearranging the components of a commercially available projection television. Our display device allows an experimenter to evaluate human visual responses to complex spectro-spatio-temporal patterns presented at naturally occurring light levels.

A perceptually optimized 3-D subband codec for video communication over wireless channels

Visual communication over wireless channels is becoming important in multimedia. Because of the limited bandwidth and high error rates of the wireless channel, the video codec should be designed to have high coding efficiency in maintaining acceptable visual quality at low bit rates and robustness to suppress the distortion due to transmission errors. The coding efficiency of a 3D subband video codec is optimized by removing not only the redundancy due to spatial and temporal correlation but also perceptually insignificant components from video signals. Unequal error protection is applied to the source code bits of different perceptual importance. An error concealment method is employed to hide the distortion due to erroneous transmission of perceptually important signals. The evaluation of each signal's perceptual importance is made first from measuring the just-noticeable distortion (JND) profile as the perceptual redundancy inherent in video signals, and then from allocating JND energy to signals of different subbands according to the sensitivity of human visual responses to spatio-temporal frequencies. Simulation results show that acceptable visual quality can be maintained in transmitting video sequences with low bit rates (<64 kbps) over the wireless channel of high error rates (up to BER=10/sup -2/), and the distortion due to erroneous transmission of coded data can be effectively suppressed. In the simulation, the noisy channel is assumed to be corrupted by the random errors depending on the average strength of the received wave and the burst errors due to Rayleigh fading.

A new metric for analyzing single-trial event-related potentials (ERPs): application to human visual P300 delta response

Visual P300 responses were recorded by using checkerboard-type stimuli. (1) High amplitude P300-delta responses were visible even in single trial event-related potentials (ERPs). (2) The algorithm based on the ‘delta response metric’ provides an efficient selection criterion for evaluation of P300 single trials in ERP ensembles. (3) The ‘universal’ character of the P300-delta response demonstrated in this report may open new avenues for the understanding of functional ERP components.

Compressing images with wavelet/subband coding

We have developed software modules (both stand-alone and in the biomedical image analysis and display package ANALYZE) that perform wavelet-based compression on both 2-D and 3-D gray scale images. We present examples of such compression on a variety of medical images, and comparisons with JPEG and other compression schemes. We also show examples of the improvements gained by true 3-D compression of a 3-D image (as opposed to 2-D compression of each slice), and discuss issues such as the treatment of edge effects and human visual system response in the context of a wavelet-based approach. Finally, we discuss extensions of the current approach to still more efficient compression schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flattening of the contrast‐detail curve for large lesions on liver CT images

This study evaluated the relative roles of physical and perceptual factors in flattening the contrast-detail (CD) curve on liver CT scans. To estimate the role of physical factors, the theoretical CD curve for a calculated theoretical observer (i.e., a nonprewhitening matched filter) was predicted using the measured noise power spectrum and measured modulation transfer function of the CT system. Another theoretical CD curve was also produced from the output of the same calculated observer after taking the human visual response function (VRF) into account. Perceptual factors were evaluated by analyzing human observers' replicated ratings of the visibility of details super-imposed on liver CT scans. The CD curve for the calculated theoretical observer was below the CD curve actually measured for nine human observers and showed no flattening. With the VRF included, flattening of the theoretical CD curves was only produced by fixed image viewing distances of less than 30 cm, a reading style not employed by the human observers. Correlated ROC analysis of observers' replicated ratings indicated that while random, intraobserver variation was present, the magnitude of this so-called observer noise was insufficient to explain the flattening of CD curves. Use of narrow display windows did not eliminate this flattening effect. The main reason for human observers' inefficient detection of large, low contrast liver lesions appears to be a consistent misuse of the image information.

Hexagonal subband image coding with perceptual weighting

A hexagonally sampled image is split into a low passband and nine passbands of one octave width and 60 deg angular orientation. The conditions to be satisfied by the filter banks for perlect reconstruction are presented. The human visual system's response to stimuli at differing spatial frequencies is then employed to shape the coding noise spectrum. Rate is allocated under a frequency-weighted mean-square-error distortion measure. A framework is presented employing either the power spectral density of the image or the variance of the subbands. Both adaptive and nonadaptive entropy coding simulations are carried out under a Laplacian source distribution. Transparent coding results are presented at rates below 1 bit/pixel.

Transform image enhancement

Blockwise transform image enhancement techniques are discussed. Previously, transform image enhancement has usually been based on the discrete Fourier transform (DFT) applied to the whole image. Two major drawbacks with the DFT are high complexity of implementation involving complex multiplications and additions, with intermediate results being complex numbers, and the creation of severe block effects if image enhancement is done blockwise. In addition, the quality of enhancement is not very satisfactory. It is shown that the best transforms for transform image coding, namely, the scrambled real discrete Fourier transform, the discrete cosine transform, and the discrete cosine-III transform, are also the best for image enhancement. Three techniques of enhancement discussed in detail are alpha-rooting, modified unsharp masking, and filtering motivated by the human visual system response (HVS). With proper modifications, it is observed that unsharp masking and HVS-motivated filtering without nonlinearities are basically equivalent. Block effects are completely removed by using an overlap-save technique in addition to the best transform.

Edge detection based on human visual response

Edge detection based on human visual response

Latencies of visually responsive neurons in various regions of the rhesus monkey brain and their relation to human visual responses

The temporal characteristics of visually responsive neurons in a variety of areas of the monkey brain are presented. These data allow a comparison to be made between the latencies of components of the human visual ERP, and the onset latencies of neurons in regions which are candidate sources of these ERP phenomena.

Adaptive filtering of biodynamic stick feedthrough in manipulation tasks on board moving platforms

A novel approach to suppress the effects of biodynamic interference is presented. An adaptive noise canceling technique is employed for substracting the platform motion correlated components from the control stick output. The effects of biodynamic interference and its suppression by adaptive noise cancellation has been evaluated in a series of tracking tasks performed in a moving base simulator. Simulator motions were in pitch, roll and combined pitch and roll. Human operator performance was assessed from the mean square values of the tracking error and the control activity. The tracking error and the total stick output signal were found to increase significantly with motion and to diminish substantially with adaptive noise cancellation, thus providing a considerable improvement in tracking performance under conditions in which platform motion were present. The adaptive filter was found to cause a significant increase in the cross-over frequency and decrease in the phase margin. Moreover, the adaptive filter was found to significantly improve the human operator visual motor response. This improvement is manifested as an increased human operator gain, a smaller time delay and lower pilot workload.