Contrast sensitivity in amblyopia: masking effects of noise

Contrast sensitivities were determined for sinusoidal gratings of varying spatial frequencies with and without the presence of a random noise pattern superimposed on the gratings. Control subjects with normal binocular vision and observers with amblyopia were tested to determine the relative effects of noise on contrast sensitivity. For both amblyopes and normal subjects, contrast sensitivities are reduced by the presence of noise. Effects are maximal at 4 cycles/degree and are minimal at low and high spatial frequencies. Dichoptic presentation of noise and gratings to opposite eyes is equivalent to monoptic results for both amblyopes and normal subjects. Masking effects are eliminated if gratings are drifted while noise patterns are static. The contrast sensitivity of amblyopes is reduced by relatively similar amounts to that of normal subjects when noise is added to the stimulus. Overall, masking effects are virtually identical for amblyopes and for subjects with normal binocular vision.