Binocular contrast interactions in cross- and iso-oriented surround modulation: measurement and modeling

[摘要] The detectability and discrimination abilities of a visual target can be improved or impaired by its surround stimulus, which is termed center-surround modulation. However, it is yet unclear whether or not surround modulation can occurs before or only after the binocular integration stage. In response, the pattern-masking paradigm was adopted to systematically measure the detection threshold of a target (horizontal Gabor, 2 cpd) under various pedestal contrasts and two surround contrasts (0 and 0.4), and with monocular, binocular and dichoptic viewing conditions. We also compared the modulation effects when the surround orientation was in parallel or orthogonal to the target orientation. With the monocular and dichoptic viewing conditions, the results showed that surround facilitation occurred at low pedestal contrast when the target and the surround mask were presented to the same eye; in contrast, surround suppression occurred at low pedestal contrast when the target and mask were presented to different eyes regardless of the pedestal's eye origin. With the binocular viewing condition, the surround modulation disappeared. To further investigate this phenomenon, the surround modulation effects under different combinations of eye origin were fitted with a two-stage binocular contrast-gain control model. The model not only successfully described the results, but also demonstrated that the surround modulation occurred before binocular summation, with interocular suppression also being involved. Furthermore, surround modulation was better modeled by using the multiplicative excitatory and multiplicative suppressive factors at the monocular level, but linearly added for interocular influence. Thus the role of surround modulation was to raise the gain of the spatial filter at the monocular level.

[学科分类] 眼科学