Fixed versus variable internal noise in contrast transduction: The significance of Whittle’s data

For human vision to recognize the contours of objects means that, as the contrast variation at the object's edges increases, so will the Mach band effect of human vision. This paper more deeply investigates the relationship between changes in the contours of an object and the Mach band effect of human vision. Based on lateral inhibition and the Mach band effect, we studied subjects' eyes as they watched images of different shapes under a fixed brightness at 34  cd/m2, with changes of contrast and spatial frequency. Three types of display were used: a television, a computer monitor, and a projector. For each display used, we conducted a separate experiment for each shape. Although the maximum values for the contrast sensitivity function curves of the displays were different, their variations were minimal. As the spatial frequency changed, the diminishing effect of the different lines also was minimal. However, as the shapes at the contour intersections were modified by the Mach band effect, a greater degree of variation occurred. In addition, as the spatial frequency at a contour intersection increased, the Mach band effect became lower, along with changes in the corresponding contrast sensitivity function curve. Our experimental results on the characteristics of human vision have led to what we believe is a new vision model based on tests with different shapes. This new model may be used for future development and implementation of an artificial vision system.

Human vision model in relation to characteristics of shapes for the Mach band effect.

Terahertz time-domain spectrometry (THz TDS) is a sensitive probe of the complex dielectric response of materials. Methods vary for converting time-domain response into final material optical parameters together with estimation of associated uncertainties. Here we point out the importance of using an accurate extraction procedure with particular emphasis on the error introduced by associated inaccuracy in thickness determination of a sample. The Total Variation (TV) method is used to estimate sample thickness to sub-micron accuracy, by constructively using the phenomena of multiple internal reflections ('ringing') within a sample. The applicability and performance of the TV methodology is discussed.

https://iopscience.iop.org/article/10.1088/1742-6596/472/1/012005/pdf

Analysis of optical thickness determination of materials by THz-TDS

There are 8 cycle/deg ripples or oscillations in performance as a function of location near Mach bands in experiments measuring Mach bands' masking effects on random polarity signal bars. The oscillations with increments are 180 degree out of phase with those for decrements. The oscillations, much larger than the measurement error, appear to relate to the weighting function of the spatial-frequency-tuned channel detecting the broadband signals. The ripples disappear with step maskers and become much smaller at durations below 25 ms, implying either that the site of masking has changed or that the weighting function and hence spatial-frequency tuning is slow to develop.

/pdf/some-observations-on-the-masking-effects-of-mach-bands-8y1b3gt29v.pdf

Some observations on the masking effects of Mach bands

This study was developed based on the lateral inhibition effect and the Mach band effect. In the study, various human vision experiments involving blurred circular 3D images of different shapes were conducted under fixed brightness and contrast, and the results of those experiments are described in detail herein, with each type of display and each shape considered and discussed separately. The results show that although the maximum values of the contrast sensitivity function curves of the various displays were different, they showed minimal variations. With changes in spatial frequency, the degree of diminution of the different lines was also minimal. However, since the shape at the intersection of the contour was modified by the Mach band effect, a greater degree of variation was generated. In addition, as the Gaussian blur was increased at the intersection of the contour lines, its Mach band effect tended to decrease as the corresponding contrast sensitivity function curve changed. Summarizing the results of the various experiments on human visual characteristics, a new visual model was developed to match the model tested with the blurred circular 3D images. This model can be used as a reference for the development of artificial vision systems and technological applications in the future.

Application of blurred circular 3D images on the human vision model

Difficulties arise in measuring masking by Mach bands because very-low-contrast signals distort the bands. [J. Opt. Soc. Am. A 17, 1147 (2000).] Adding narrow luminance increments (bright bars) in the dark Mach band widens the dark band; adding decrements (dark bars) narrows the dark band, and conversely in the bright bands. Randomizing signal polarity prevents observers from using the distortion of the Mach bands as a cue to the presence of the signal. We measured (two-alternative-forced-choice) Mach bands' masking of randomly selected bright (incremental) or dark (decremental) bars. Detection was worse in both dark and bright Mach bands than on the neighboring plateaus. Separate analysis of trials containing only one polarity signal revealed 9-cycle/deg oscillations in performance as a function of location. Oscillations in the two polarities were approximately 180 degrees out of phase.

NJ Hill

Papers

Masking effect produced by Mach bands on the detection of narrow bars of random polarity