CHARACTERIZATION OF THE HUMAN VISUAL-SYSTEM THRESHOLD PERFORMANCE BY A WEIGHTING FUNCTION IN THE GABOR DOMAIN

As evidenced by many physiological and psychophysical reports, the rec eptive fields of the first-stage set of mechanisms of the visual proce ss fit to two-dimensional (2D) compactly supported harmonic functions. The application of this set of band-pass filter functions to the inpu t signal implies that the visual system carries out some kind of conjo int space/spatial frequency transform. Assuming that a conjoint transf orm is carried out, we present in this paper a new characterization of the visual system performance by means of a weighting function in the conjoint domain. We have called this weighting function (in the parti cular case of the Gabor transform) the Gabor stimuli Sensitivity Funct ion (GSF) by analogy with the usually employed weighting function in t he Fourier domain: the Contrast Sensitivity Function (CSF). An analyti c procedure to obtain this conjoint weighting function from the psycho physical measurements of the CSF is derived. The accuracy of the proce dure is proved showing the equivalence between some experimental Fouri er weighting functions (2D CSFs), and the corresponding GSFs. The main advantage of this new characterization is that a weighting function i n a space/spatial frequency domain can account for spatially variant b ehaviour, which cannot be included in a unique CSF, so a single GSF wo uld be needed to include extra-foveal and large eccentricity behaviour . One example is given of how non-homogeneous systems can be easily ch aracterized in this way.