Ocular aberrations are caused by spatial phase nonuniformities in the wavefront exiting the eye. Mathematical techniques like phase imaging or curvature sensing are also capable of providing wavefront estimations. A wavefront sensor is a device for measuring the aberrations of an optical wavefront. Ocular aberrations are distortions in the wavefront passing through the pupil of the eye. Propagation of a curved wavefront always leads to amplitude variation. A common method is the Roddier test, also called wavefront curvature sensing. Diffraction occurs when a wavefront encounters an object. The mean wavefront perturbation in each pixel is calculated. The captured images are processed by a computer to calculate the optical wavefront errors. Therefore, a plane wave is reshaped into a parabolic wavefront by a liquid crystal lens. The arriving energy from the RF wavefront is launched into both waveguide feedhorns. Another cause for disturbance of the spherical wavefront is the "truncation effect". By definition, all points on the wavefront have the same propagation time from "A". In chordates, segmentation is coordinated by the clock and wavefront model. The precedence effect or law of the first wavefront is a binaural psychoacoustical effect.