本研究旨在探究邊緣空間頻率 (remote spatial frequency) 訊息在不同觀測條件(單眼觀測、雙眼觀測、雙眼分視) 下⾃然影像的結構對⿑ (structure alignment)與否的對⽐調節控制機制。在本研究中，我們採⽤遮蔽實驗派典 (pattern masking paradigm) 來量測受試者對⽬標刺激在不同遮蔽刺激下的差異閾。⽬標刺激為經過帶通濾波器 (bandpass-filter) 過濾空間頻率之⾃然影像。在實驗⼀中我們採⽤三種遮蔽刺激，分別為：帶通濾波遮蔽刺激，與⽬標刺激相同之刺激；無濾波 (non-filter) 遮蔽刺激，為原始的⾃然影像；陷波濾波 (notch-filter)遮蔽刺激，將⽬標刺激之空間頻率過濾掉的⾃然影像，僅帶有邊緣空間頻率。在實驗⼆中，我們採⽤另⼀種遮蔽刺激：旋轉 (rotated) 遮蔽刺激，在這個配置下遮蔽刺激本⾝為原始的⾃然影像，⽽⽬標刺激物則被旋轉。此外，所有的差異閾都會在三種不同的觀測條件下被量測。實驗⼀的結果顯⽰，帶通濾波遮蔽刺激的差異閾函數在單眼視覺下呈現出帶有促進及遮蔽效果的典型的勺⼦型；無濾波遮蔽刺激以及陷波濾波遮蔽刺激的差異閾函數在單眼視覺下卻僅有遮蔽效果。這個結果⽀持邊緣空間頻率訊息在對⽐調節控制機制中會造成更⼤的對⽐抑制效果；亦有可能是較寬的空間頻率與⽬標刺激有所重疊所致。實驗⼆的結果顯⽰，對⽐於無濾波遮蔽刺激，旋轉遮蔽刺激完全沒有呈現出促進效果。⽽這個結果⽀持⾃然影像的結構對⿑對於在對⽐調節控制機制中產⽣促進效果⽽⾔是相當關鍵的。除此之外，模型模擬的結果顯⽰陷波濾波遮蔽刺激在對⽐調節控制機制中仍產⽣了些微的激發效果，這個激發可能是來⾃其完整的⾃然影像的結構訊息；亦有可能是較寬的空間頻率與⽬標刺激有所重疊所致。

The purpose of this study was to probe how remote spatial frequency information affects contrast gain control and to investigate the structure alignment of natural scenes in contrast gain control in different viewing conditions. The pattern masking paradigm was used to measure the discrimination threshold of natural scene images (targets) that were bandpass-filtered in the presence of pedestals of different contrasts. In experiment 1, three types of pedestals were adopted. The bandpass-filtered pedestal was the same as the target, the non-filtered pedestal was the original image, and the notch-filtered pedestal was filtered to remove the spatial frequency of the target information. In experiment 2, a rotated pedestal was adopted to compared with non-filtered pedestal of experiment 1. In this condition, the target was randomly rotated. The thresholds were compared among monocular, binocular, and dichoptic viewing configurations. The results of Experiment 1 showed that a classic dipper shape that was revealed for the bandpass-filtered pedestal was damaged for the non-filtered and notch-filtered pedestals. This suggests that the remote spatial frequency causes stronger inhibition in contrast gain control, or caused by the wider spatial frequency bandwidth that was overlapped to the target. The results of Experiment 2 showed that the rotated pedestal lost the
facilitation effect at low pedestal contrasts whereas the nonfiltered pedestal did not. This finding suggests that the structural alignment is critical to produce the
facilitation effect in contrast gain control. Furthermore, the model fitting result revealed that the notch-filtered pedestal caused slight excitation, which may actually cause by the structural alignment or the wider spatial frequency bandwidth that was overlapped with the target.

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