深度與大小

Chapter 10

深度知覺之線索取向(cue approach to depth perception)

• 尋找視覺影像（ proximal stimulus ）中與環境的深度（ distal stimulus ）有關的線索訊息（ cues ），我們透過經驗建立這些深度線索與實際深度的關連性，而造成深度知覺。

眼球運動線索（ Oculomotor cues ）

• 根據我們對於眼球位置與眼球肌肉緊張度的感受，而產生的深度線索– 限近距離有用（手臂距離）

• Convergence– 因需觀看近物，兩眼球向內移動– 感受到的

convergence 愈多，表示物體距離愈近

– 雙眼線索

• Accommodation– 隨物體距離不同，水晶體形狀會改變以利聚焦

– 水晶體愈平，表示距離愈遠– 單眼線索

眼球運動線索（ Oculomotor cues ）

單眼線索 (monocular cues)

• 圖畫線索（ pictorial cues ）– Alberti’s window

• 遮蔽（ occlusion ）– 提供相對距離線索– 被遮蔽者較遠

• 相對高度– 底部較高的離觀察者較遠– 但是，物體若落在水平線以上，那麼底部較低的較遠

單眼線索 (monocular cues)

Fig. 8-3, p. 170

• 相對大小– 小的比較遠 (demo-monster)

• 透視匯聚 (perspective convergence)– 匯聚端較遠

單眼線索 (monocular cues)

• 熟悉的尺寸– 原本較大的被認為較遠– 雙眼觀察則沒有這種錯覺

單眼線索 (monocular cues)

• 空氣透視（ atmosphere perspective ）

• 不清楚的比較遠

單眼線索 (monocular cues)

Fig. 8-5, p. 171

• 質地遞變– 密的較遠

單眼線索 (monocular cues)

• 陰影– 陰影的特性協助瞭解物體在空間中的位置

單眼線索 (monocular cues)

• 運動線索 (movement-produced cues)– 觀看者運動而產生的深度線索（單眼）

• 運動視差（ motion parallax ）– 遠的物體動得慢，近的物體動得快 link– 比凝視點近的物體，其移動與運動方向相反；比凝視點遠的物體，其移動與運動方向相同

Fig. 8-10a, p. 173

Fig. 8-10b, p. 173

Table 8.1 Range of effectiveness of different depth cues

雙眼深度訊息• 雙眼像差（ Binocular disparity ）

– 左右眼的影像差異

Figure 8.11 Location of images on the retina for the “Two Eyes: Two Viewpoints” demonstration. (a) Both images are on the fovea when the left eye is open. (b) The images are on different places on the retina when the right eye is open.

• 立體感（ stereopsis ）– 對應點（ corresponding retinal points ）

雙眼深度訊息

Figure 8.13 (a) When the lifeguard looks at Frieda, the image of Frieda, Susan, and Harry fall on corresponding points on the lifeguard’s retinas, and the images of the other swimmers fall on noncorresponding points. (b) The locations of the images of Susan, Frieda, and Harry on the lifeguard’s retina.

– horopter• 是一個想像的圓，凝視點落在上面，而其上的每個物體會落在兩眼網膜的對應點

• 不在 horopter 上的物體，會落在雙眼網膜的非對應點（ noncorresponding points ），並形成像差角（ angle of disparity ）– C 與 X 之夾角

• 離 horopter 愈遠，像差角愈大– L 與 Y 之夾角

• 交叉型像差（ crossed disparity ） : 落在 horopter 之前的物體形成交叉型像差，顯示物體比 horopter 近

• 非交叉型像差（ uncrossed disparity ） : 落在 horopter 之後的物體形非成交叉型像差（網膜上的落點向內） ，顯示物體比 horopter 遠

Absolute disparity for Carole (how far an object is from the horopter)

Horopter

Absolute disparity for Frieda

Horopter

• Relative disparity is the difference between the absolute disparity of two objects.• Absolute disparity

– Frieda: 0 °– Carole: 26 °

• Relative disparity: 26 ° – 0 ° = 26 °– Offering an advantage as an observer

shifts his fixation

• Stereoscope (1800’s)

Figure 8.16 The two images of a stereoscopic photograph. The difference between the two images, such as the distances between the front cactus and the window in the two views, creates retinal disparity. This creates a perception of depth when (a) the left image is viewed by the left eye and (b) the right image is viewed by the right eye.

Fig. 8-18, p. 176

• 3-D movies– A polarized filter allows only

light travelling in one position to pass through. It is made of parallel micro-sized slits that block out all but one position of wave.

– A wave in the vertical planepasses through a verticalpolarized filter.A wave in the horizontal planepasses through a horizontalpolarized filter, but would not beable to pass through a verticalpolarized filter.

• There are two types of filters in 3-D glasses (i.e. vertical and horizontal). So, one side allows only light travelling in one position to pass through while the other side allows light of the opposite position to pass.

• 3-D movies are filmed with a stereoscopic camera that records video much like how the Pathfinder IMP above records images. When a 3-D movie is played, two projectors are used to display both perceptions. Each projects a video polarized (with a filter) onto the screen. Wearing the 3-D glasses, each eye can only take in light from one of the projectors. Therefore, each eye receives a different image. Your brain interprets these two separate images and combines them into one 3-D picture.

• Next time you view a 3-D movie, take two set of glasses. Place the right-eye filter and place it over the left-eye filter. It's dark. That because the vertical and horizontal filters are combined and no light can enter. They cancel each other.

• 立體相機

• 裸眼觀看

Fig. 8-17, p. 176

Also see demo

• 純由像差造成的立體感– 隨機點立體圖（ Random dot stereogram ） (Julez, 1971)

– 深度感只能歸因於像差

– 左右眼影像如何 match ？對應問題（ The correspondence problem ）

• 根據單眼特徵作匹配？• RDS 呢？

其他生物的深度知覺

• Animals use the range of cues that humans use

• Frontal eyes– binocular disparity.

• Lateral eyes– wider view.

– important for watching for predators

• Bats– echolocation

Depth Perception in Other Species

• Locusts use motion parallax to judge distance.

• Bats use echolocation to judge the distance of objects in the dark.

– They emit sounds and note the interval between when they send them and when they receive the echo.

Figure 10.22 When a bat sends out its pulses, it receives echoes from a number of objects in the environment. This figure shows the echoes received by the bat from (a) a moth located about half a meter away; (b) a tree, located about 2 meters away; and (c) a house, located about 4 meters away. The echoes from each object return to the bat at different times, with echoes from more distant objects taking longer to return. The bat locates the positions of objects in the environment by sensing how long it takes the echoes to return.

Figure 8.20 Top: gradient stimuli. Bottom: response of neurons in the parietal cortex to each gradient. This neuron fires to the pattern in (c), which the monkey perceives as slanting to the left. (From Tsutsui et al., 2002, 2005.)

深度知覺的生理基礎• A neuron in the parietal cortex of a monkey

Figure 8.21 Disparity tuning curve for a disparity-sensitive neuron. This curve indicates the neural response that occurs when stimuli presented the left and right eyes create different amounts of disparity. (From Uka & DeAngelis, 2003.)

• 雙眼深度細胞（ Binocular depth cell ）或像差選擇性細胞（ disparity selective cell ）– 當兩眼影像具有像差時反應最佳

Connecting Binocular Disparity and Depth Perception

• Experiment by Blake and Hirsch

– Cats were reared by alternating vision between two eyes.

– Results showed that they:

• had few binocular neurons.

• were unable to use binocular disparity to perceive depth.

– 單眼養育的貓，皮質雙眼深度細胞數量甚少– 敏感期（ sensitive period ）為六個

• Neural Responding & Depth Perception– DeAngelis et al. (1998)

• Monkey training: depth created by images with different absolute disparity to each eye

• Monkey shifted its depth judgment because of a different group of disparity-selective neurons activated.

– Primary visual cortex Ventral and dorsal streams

大小知覺 (size perception)• 大小知覺與深度知覺有關

Figure 8.25 (a) The visual angle depends on the size of the stimulus (the woman in this example) and its distance from the observer. (b) When the woman moves closer to the observer, the visual angle and the size of the image on the retina increases. This example shows how halving the distance between the stimulus and observer doubles the size of the image on the retina.

Figure 8.26 The “thumb” method of determining the visual angle of an object. When the thumb is at arm’s length, whatever it covers has a visual angle of about 2 degrees. The woman’s thumb covers half the width of her iPod, so we can determine that the visual angle of the iPod’s total width is about 4 degrees.

Fig. 8-27, p. 182

• Holway & Boring (1941)– 測驗刺激距離雖然會改變，但投射的視角大小維持不變– 受試者調整比較刺激（固定位置於 10ft 處）的大小至與測驗刺激相同

– 1- 提供正常深度訊息2- 單眼3- 透過窺視孔4- 走道上加裝布幔

– 顯示大小判斷除運用視角訊息，還要仰賴深度知覺

測驗刺激實際大小隨距離遞增

– 太陽與月亮的大小感覺差不多– 在飛機上看地面的房子像火柴盒

無法判斷或

不熟悉它們的實際

距離

用視角判斷

• 大小恆常性（ size constancy ）– 即使距離改變，對於大小的知覺仍維持恆定 – 是考慮深度訊息後計算的結果—大小 - 距離調節機制（ size-distance scaling mechanism ）

• demo

• S=K(R x D)

S- 知覺大小， K- 常數， R- 網膜影像大小， D- 距離

– Emmert’s law– Familiar size and texture gradient information也都有助於維持大小恆常性

Fig. 8-30, p. 183

Fig. 8-31, p. 184

Emmert’s law:K(R x D) = S

Fig. 8-32, p. 184

Fig. 8-33, p. 185

錯覺• Muller-Lyer illusion

– 誤用大小恆常性調節機制 S=K(R x D)

• 但無法 解釋啞鈴版或書本版的錯覺

– 線索衝突：大小判斷利用兩種線索• 實際的線長圖形的長度

• Ponzo illusion– 誤用大小恆常性調節機制

• Ames room

Fig. 8-40, p. 187

Figure 8.41 The Ames room, showing its true shape. The woman on the left is actually almost twice as far away from the observer as the woman on the right; however, when the room is viewed through the peephole, this difference in distance is not seen. In order for the room to look normal when viewed through the peephole, it is necessary to enlarge the left side of the room.

• 月亮錯覺（ Moon illusion ）– 表面距離理論（ apparent distance theory ）

• 地表附近有許多建築或其他結構，提供深度線索，所以月亮看來較中天遠

– 角度大小對照理論 (angular size contrast theory)• 月亮在中天時，周遭背景較大，所以顯得較小

2005/6/23

Figure 8.42 An artist’s conception of the moon illusion showing the moon on the horizon and high in the sky simultaneously.

Figure 8.43 When observers are asked to consider that the sky is a surface and are asked to compare the distance to the horizon (H) and the distance to the top of the sky on a clear moonless night, they usually say that the horizon appears farther away. This results in the “flattened heavens” shown above.

– 表面距離（ apparent distance ）理論• 由窺視孔看，則使錯覺消失

– 大小對比理論– 其他因子

• 空氣透視• 顏色• 輻輳作用

• 距離知覺的判斷也受所付出的努力影響

Figure 8.44 Results of Witt et al.’s (2004) experiment. For each of the conditions, larger distance estimates were associated with greater effort.

• 距離知覺的判斷也受所付出的努力影響