Spatial Frequency tuning functions and Contrast Sensitivity at Different Eccentricities in the Visual Field

Abstract

Threshold and suprathreshold vision. The human luminance spatial frequency contrast sensitivity function (CSF) has been well studied using psychophysical measurements by detecting spatial frequency (SF) grating patterns at threshold [1], [2]. Threshold CSFs at different eccentricities have proven to be quite useful in both basic and clinical vision research. However, near threshold, the CSF is measured at a linear area of the saturating contrast-response curve. In contrast, most of our everyday vision may be at suprathreshold levels, and thus may function most of the time at the nonlinear area of the contrast-response curve. Furthermore, since the CSF is measured near threshold, it is quite possible that only the most sensitive retinal or LGN cells may contribute to the measured CSF. Since the M (magnocellular) cells in retina and LGN are about 10 times more sensitive than the P (parvocellular) cells at low to medium spatial frequencies [3], [4], the measured threshold CSF may reflect more M cell contributions. There have been recent attempts to measure suprathreshold contrast responses using contrast matching techniques [5], [6], [7]. These results show that the contrast response functions at suprathreshold levels are flatter than CSF curves measured at threshold. However, whether the results from contrast matching reflect the spatial frequency tuning functions at suprathreshold for human vision is still unclear since contrast matching is quite different from threshold measurements [4].