亮度對比於深度知覺判斷之角色

Role of Luminance Contrast in Depth Perception

陳姵吟(Pei-Yin Chen)

指導教授 ： 陳建中

國立臺灣大學/理學院/心理學研究所/博士(2019年)

https://doi.org/10.6342/NTU201904254

摘要

由於人類雙眼位於臉上不同的位置，因此觀看的景象投射到兩眼視網膜上會產生像差，視覺系統會根據此雙眼像差形成立體深度知覺。由於雙眼像差的大小由物體與觀看者間的物理距離所決定，因此一般認為由雙眼像差產生的深度知覺不會隨著影像亮度對比而改變。然而本研究顯示影像亮度對比會影響由雙眼像差產生的深度知覺，且此研究結果無法被現有的雙眼像差能量模型所解釋，因此我們提出一個雙眼像差處理模型以解釋影像亮度對比對由雙眼像差產生之深度知覺的影響，此模型包含亮度對比增益機制及雙眼像差平均機制。本研究以四個心理物理學實驗檢驗亮度對比於此模型各階段如何影響深度知覺，並透過一個功能性磁振造影實驗探討此亮度對比對深度知覺之影響發生在視覺處理的哪階段。首先，我們操弄隨機點陣立體視覺圖形的亮度對比確認影像亮度對比的改變如何影響深度知覺，研究結果顯示深度知覺與影像亮度對呈非線性關係，表示雙眼像差的處理過程包含亮度對比增益機制。此外，當操弄影像的立體表面結構時，研究結果亦顯示立體表面結構的視差梯度及波紋周期數皆會影響深度知覺。我們更進一步分別操弄左右兩眼所見之影像亮度對比相同與否，來探討雙眼影像亮度對比如何整合並影響立體知覺。研究結果顯示深度知覺會隨雙眼間亮度對比差異的增加而下降。最後，我們同時操弄帶通雜訊之立體視覺圖形的亮度對比及空間頻率，了解立體知覺是否會隨影像空間頻率而改變。研究結果顯示帶通雜訊之立體視覺圖形的深度知覺雖然會隨影像亮度對比變化，但不受影像空間頻率影響。以上研究結果皆可被我們提出之雙眼像差處理模型中的亮度對比增益機制及雙眼像差平均機制所解釋，說明亮度對比在深度知覺運算上，扮演重要的角色。除此之外，功能性磁振造影的研究結果亦顯示，腦區V3A及KO可能是參與亮度對比對深度知覺之影響的腦區。

關鍵字

立體視覺 ； 雙眼視差 ； 亮度對比增益機制 ； 雙眼像差平均機制 ； 心理物理學 ； 功能性磁振造影

並列摘要

In stereo perception, the visual system combines a pair of horizontally shifted images in the two eyes to generate a 3D percept. The difference in horizontal location of the images seen by the left and right eyes is called binocular disparity and is defined only by the geometry of a scene. Thus, the perceived depth from disparity is generally considered to be independent from luminance contrast. However, luminance contrast does affect stereo perception. Such an effect cannot be explained by existing disparity energy models, because they predict no effect of luminance contrast on depth perception. We proposed a model that involves a contrast gain control followed by disparity averaging to account for the luminance contrast effect on perceived depth. In this study, we conducted four psychophysical experiments to examine each part of the working model we proposed in order to understand the role of luminance contrast in disparity processing, and one fMRI experiment to explore the related brain areas to the luminance contrast effect on perceived depth from disparity. We first used random-dot stereograms as stimuli to test the effect of luminance contrast on perceived depth. Our results suggested a profound nonlinear luminance contrast effect on perceived depth from disparity. We then varied the depth modulation frequency to investigate the effect of 3D surface configuration on perceived depth. Our results showed that both the disparity gradient and the number of modulation cycles had an effect on perceived depth from disparity. We further manipulated the interocular luminance contrast difference in the random-dot stereogram to explore the binocular summation in depth perception. Our results demonstrated that the perceived depth was determined by both luminance contrast level and interocular luminance contrast difference. Finally, we changed the spatial frequency of the bandpass noise patterns to test whether the spatial frequency of the test images affected the perceived depth. Our results showed that the perceived depth did not vary with the image spatial frequency. All these results can be accounted for by the contrast gain control mechanism and disparity averaging operation in our model. Moreover, our neuroimaging evidence showed that such luminance contrast effects on perceived depth might relate to the disparity specific luminance contrast activations in cortical area V3A and KO. In sum, we demonstrated that luminance contrast plays an important role in disparity processing.

並列關鍵字

stereopsis ； binocular disparity ； contrast gain control ； disparity averaging ； psychophysics ； fMRI

參考文獻

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