運動知覺（ Perceiving movement ）

Chapter 8

運動知覺有多重要？• 協助個體瞭解周遭發生的事– 如果喪失運動知覺…… ..– 運動失認症（ motion

agnosia ）• 無法用茶壺倒茶• 與人談話有困難• 最感困難的是

–人和東西突然出現 /消失

• 運動吸引注意力– Attentional capture

• 運動提供物體的訊息（ VL1,2 ）– 透過刺激的運動，使原本不清楚的結構（形狀）變得清楚可辨

Fig. 9-3a, p. 198

Fig. 9-3b, p. 198

Fig. 9-3c, p. 198

• 真實運動• 似動運動（ apparent motion ）

– Exner (1875)– 電影 / 動畫 / 霓虹燈– Wertheimer

• AM-illusory contour

運動知覺的研究

(No motion)

真實 vs. 似動運動 -

激發視皮質的相近區域

• 誘發運動（ induced movement ） (VL 12)– 周遭的運動引發自身運動的錯覺

• 如，坐在靜止火車中等待會車，相鄰車廂的移動引發自身車廂移動的錯覺

• 運動後效（ motion aftereffect ） (VL 13-14)– 如瀑布錯覺（ waterfall illusion)

• http://www.bu.edu/smec/lite/perception/waterfall/

– spiral motion aftereffect• http://www.michaelbach.de/ot/mot_adaptSpiral/

index.html

• 不同條件下的運動知覺

– 依照視覺的生態取向（ JJ Gibson), 運動知覺的解釋繫於分析視覺環境所提供的運動訊息

• a. 光陣列中局部擾動（ local disturbance ）• b. local disturbance• c. Global optic flow

– 依照視覺的生理學取向，應該設法瞭解運動知覺與神經激發之間的關係

Motion of a Stimulus Across the Retina

• 腦如何解讀網膜上刺激運動的訊息 ?– 透過複雜細胞

（ complex cell ）的處理？

– 恐怕不是

• 框架問題 （ the aperture problem ）– 兩種情況下，神經元的反應相同

• 解決框架問題？– responses of a number

of directionally selective neurons are pooled. Their signals are sent to--

• MT cortex (the where/action stream).

– Neurons on the striate cortex respond to movement of ends of objects.

Figure 9.15 (a) Some of the nuclei in the dorsal and ventral streams. The MT cortex, which is a module for movement perception, is in the dorsal stream, and the IT cortex, which is a module for form perception, is in the ventral stream. (b) The location of the MT and IT cortex in the brain.

解決方式—統整不同區域的訊息

Module for movement perception

• MT 神經元與 global motion 的偵測有關– 相關 0.8% -- baseline firing of MT neuron

chance detection相關 12.8%-- faster firing than baseline highly accurate detection

Motion of arrays of dots on the retina

Coherence of dot movement↑

Firing of the MT neurons↑ Judgment accuracy of movement direction↑

• Lesioning experiment– Normal monkeys can detect motion with

coherence of 1 or 2%.

– Monkeys with lesions in MT cortex cannot detect motion until the coherence is 10 to 20%.

• microstimulation

• Stimulating MT neurons that preferred downward direction

• Monkeys’ direction judgments were affected.

• Downward + Rightward

眼球移動的角色Corollary discharge theory

• 運動知覺仰賴三種訊號– 動作訊號（ motor signal, MS ）– 附帶釋放訊號（ corollary discharge signal, CDS ）– 影像移動訊號（ image movement signal, IMS ）

• 當 CDS 或 IMS 到達比較器（ comparator ）時，運動知覺產生；但是當 CDS 與 IMS 同時到達比較器（ comparator ）時，沒有運動知覺

Figure 8.18 According to the corollary discharge model (a) when a motor signal (MS) to move the eyes is sent to the eye muscles, so the eye can follow a moving object, there is a corollary discharge signal (CDS), which splits off from the motor signal. (b) When the CDS reaches the comparator, it sends a signal to the brain that the eye is moving, and motion is perceived.

Figure 9.8 How inputs to the comparator (circle) affect movement perception. When the comparator receives either the corollary discharge signal (CDS) alone, as in (a), or the image movement signal (IMS) alone, as in (b), it sends a movement signal to the cortex, and movement is perceived. When the comparator receives both the CDS and IMS signals, a movement signal is not sent to the cortex, and no movement is perceived.

Figure 9.9 In all four examples shown in the figure, a signal is sent to the eye muscles, and a corollary discharge is generated. However, no image movement signal is generated, so movement is perceived. See text for details.

Fig. 9-10, p. 203

– 沒有 IMS ，但 CDS 引發運動知覺的可能方式 – 這些行為證據支持 corollary discharge theory

Fig. 8.23, p. 191

真實運動神經元

當眼球與刺激都運動時就不活躍

知覺組織與運動知覺

• 運動造成知覺組織– Biological motion

• animal• male vs. female• Neurons in monkey’s

superior temporal sulcus respond to man walking forward but less so for other directions of walking

Fig. 9-17, p. 208

生物運動（ biological motion ）http://www.biomotionlab.ca/Demos/BMLwalker.html

Figure 9.18 Frames from the stimuli used by Grossman and Blake (2001). (a) Sequence from the point-light walker stimulus. (b) Sequence from the scrambled point-light stimulus.

• Determining whether motion was biological or scrambled– Noise added led to 71%

accuracy.– Transcranial magnetic

stimulation (TMS) applied only to STS caused a decrease in ability to detect biological motion.

Biological motion Scrambled stimulus

Biological motion + noise

Biological motion + noise

Biological motion stimulus

• Other neurons respond to point light walker

• Also, for human, PET activity increases in STS when presented with man walking

• 暗示運動（ Implied motion ）– 靜態圖像隱涵運動的型態

• 表徵動量（ representational momentum)– 圖像隱涵中的運動會在觀看者的心中持續完成

– 「遮蔽」經驗法則• 運動的物體落於同一位置時可能會被遮蔽• Duck demo