Pattern specificity of contrast adaptation.

Contrast adaptation is specific to precisely localised edges, so that adapting to a flickering photograph makes one less sensitive to that same photograph, but not to similar photographs. When two low-contrast photos, A and B, are transparently superimposed, then adapting to a flickering high-contrast B leaves no net afterimage, but it makes B disappear from the A+B picture, which now simply looks like A

Spectral triangulation molecular contrast optical coherence tomography with indocyanine green as the contrast agent

We report a new molecular contrast optical coherence tomography (MCOCT) implementation that profiles the contrast agent distribution in a sample by measuring the agent's spectral differential absorption. The method, spectra triangulation MCOCT, can effectively suppress contributions from spectrally dependent scatterings from the sample without a priori knowledge of the scattering properties. We demonstrate molecular imaging with this new MCOCT modality by mapping the distribution of indocyanine green, a FDA-approved infrared red dye, within a stage 54 Xenopus laevis

Materials Contrast in Piezoresponse Force Microscopy

Piezoresponse Force Microscopy contrast in transversally isotropic material corresponding to the case of c+ - c- domains in tetragonal ferroelectrics is analyzed using Green's function theory by Felten et al. [J. Appl. Phys. 96, 563 (2004)]. A simplified expression for PFM signal as a linear combination of relevant piezoelectric constant are obtained. This analysis is extended to piezoelectric material of arbitrary symmetry with weak elastic and dielectric anisotropies. This result provides a framework for interpretation of PFM signals for systems with unknown or poorly known local elastic and dielectric properties, including nanocrystalline materials, ferroelectric polymers, and biopolymers.Comment: 20 pages, 3 figures, 1 table, accepted to Appl. Phys. Lett. (without Appendices), algebraic errors were correcte

Contrast sensitivity evaluation with filter contact lenses in patients with retinitis pigmentosa: a pilot study

Purpose: the aim of this pilot study was to test whether retinitis pigmentosa patients would benefit from filter contact lenses as an effective optical aid against glare and photophobia. Methods: fifteen subjects with retinitis pigmentosa were enrolled in this study. All of them were evaluated with filter soft contact lenses (MaxSight), filter glasses (CPF 527) and without filters (control). All patients were assessed for the three aid conditions by means of best corrected visual acuity (BCVA), contrast sensitivity (without glare and with central and peripheral glare)(CSV-1000) and a specific subjective questionnaire about quality of vision. Results: BCVA was slightly better with filters than without filter but the differences were not statistically significant. Contrast sensitivity without glare improved significantly with the contact lenses (p<0.05). The central glare had significant differences for the frequencies of 3 cpd and 18 cpd between the contact lens filter and the control group (p=0.021 and p=0.044, respectively). For the peripheral glare contrast sensitivity improved with contact lens versus control group for highest frequencies, 12 and 18 cpd (p<0.001 and p=0.045, respectively). According to the questionnaire the contact lens filter gave them more visual comfort than the glasses filter under the scenarios of indoors glare, outdoors activities and indoors comfort. Conclusion: the filter contact lenses seem to be a good option to improve the quality of vision of patients with retinitis pigmentosa

Differential Phase-contrast Interior Tomography

Differential phase contrast interior tomography allows for reconstruction of a refractive index distribution over a region of interest (ROI) for visualization and analysis of internal structures inside a large biological specimen. In this imaging mode, x-ray beams target the ROI with a narrow beam aperture, offering more imaging flexibility at less ionizing radiation. Inspired by recently developed compressive sensing theory, in numerical analysis framework, we prove that exact interior reconstruction can be achieved on an ROI via the total variation minimization from truncated differential projection data through the ROI, assuming a piecewise constant distribution of the refractive index in the ROI. Then, we develop an iterative algorithm for the interior reconstruction and perform numerical simulation experiments to demonstrate the feasibility of our proposed approach

The functional role of contrast adaptation

Prolonged inspection of high contrast sinewave gratings increases the contrast required to detect gratings having a similar spatial frequency and orientation. The functional role of such adaptation has, however, in the past, eluded disclosure. We here show that 5 min adaptation to a 2 c/deg sinewave grating of 0.8 contrast changes the observer's ability to discriminate the contrast level of a subsequently presented grating of the same spatial frequency and orientation. Similar to the threshold elevation effect, the observers required more incremental contrast for background contrast levels between 0.1 and 0.4 following adaptation. However, for contrast levels above 0.5, the observers required less delta contrast, following adaptation, to correctly discriminate which of two gratings was incremented in contrast. A simple model for adaptation is proposed to account for the findings which is based on a shift in the semi-saturation constant of the detector's contrast-response function. According to this model, adaptation acts to linearize the underlying mechanism's response in the region near the prevailing contrast level

Optical contrast in near-field techniques

In this paper results of experiments with a scanning near-field optical microscope with shear-force feedback are presented. The setup will be described and the shear-force signal as function of distance is shown. Images of latex spheres and Langmuir- Blodgett layers of pentacosa-acid with about 100 nm lateral resolution are presented which show a true optical contrast due to fluorescence and polarization