week 4

Question 1

Which brain areas are involved in motion processing?

Answer 1

Motion processing begins in V1 and continues into the dorsal stream, including V2, V3, V5/MT, MST, V6, and STS. Note that the retina and LGN do not contain motion‐sensitive cells.

Question 2

What is the role of the retina and LGN in motion detection?

Answer 2

There are no motion‐detector cells in the retina or LGN. Motion processing starts centrally in V1 and beyond

Question 3

What are the characteristics of V1 and V2 in relation to motion processing?

Answer 3

V1 and V2 contain cells with small receptive fields that respond to simple stimuli (e.g., lines and elementary directional motion such as left–right). They are not tuned for speed and are not specialized for complex motion processing

Question 4

How is V3 (and its subdivisions) specialized for motion detection?

Answer 4

V3, including areas VP, V3B, and V3A, has larger receptive fields than V1/V2 and is specialized for detecting the motion of complex stimuli (such as textured patterns)

Question 5

Describe how cells in V5/MT respond to motion

Answer 5

Cells in V5/MT have large receptive fields and respond to motion across a range of stimuli (including random dot patterns). They are tuned for specific directions and speeds, can detect simple patterns (like expansion–contraction), and include opponent motion detectors that assess the balance of signals from cells preferring opposite directions

Question 6

What properties characterize neurons in MST?

Answer 6

MST neurons have very large receptive fields, respond to the motion of virtually any stimulus (even random dots), and are tuned for both direction and speed. They process complex motion patterns (e.g., those generated by locomotion), respond to static images that imply motion, and use vestibular cues to help distinguish self-motion

Question 7

What is the function of the V6 area in motion processing?

Answer 7

V6 primarily responds to self-induced motion. It helps differentiate whether movement on the retina is due to the environment’s motion or to the observer’s own eye or head movements

Question 8

How does the brain differentiate between retinal motion caused by an object and motion caused by self-movement?

Answer 8

The brain uses a copy of the self-motion signal (generated by intentional eye/head movements) to subtract the effects of self-movement. This integration of inflow (sensory input) and outflow (motor command copy) helps keep the perception of the external world stable

Question 9

Explain the concepts of inflow and outflow in motion perception

Answer 9

“Inflow” refers to the sensory input—the motion of images on the retina—whereas “outflow” refers to the knowledge from motor commands about intentional eye or head movements. Together, they allow the visual system to correctly interpret whether an object truly moves in the environment

Question 10

What is apparent motion, and how is it perceived?

Answer 10

Apparent motion is the illusion of continuous, fluid movement created when an object appears in position A and then position B within a short enough time interval and spatial gap. Even though the object doesn’t appear at every intermediate point, the brain interprets the sequence as smooth motion

Question 11

Under what conditions does apparent motion fail to be perceived as fluid motion?

Answer 11

If the time delay between the two positions is too long or the spatial gap is too great, the brain perceives the change as a mere displacement rather than continuous motion

Question 12

How are movies and TV designed to exploit apparent motion?

Answer 12

Movies typically show one image every 40 ms, while TV displays may update sets of strips every 20 ms. This rapid presentation of successive still images fools the brain into perceiving fluid motion, avoiding the perception of flicker

Question 13

What is the wagon wheel illusion, and what does it reveal about motion processing?

Answer 13

The wagon wheel illusion (reverse motion phenomenon) occurs when repetitive patterns—such as the spokes of a wheel—are sampled at discrete intervals. Depending on the timing, the wheel’s motion can appear to reverse or freeze, demonstrating how the brain interprets temporal gaps in information

Question 14

How does motion sensitivity develop in infants?

Answer 14

Basic sensitivity to motion begins around 6–8 weeks of age, although initial capabilities (such as discriminating motion direction or performing smooth pursuit) are rudimentary. Rapid improvements occur between 6 and 14 weeks, and sensitivity to looming stimuli may be present very early or even at birth

Question 15

What is motion blindness (akinetopsia), and which neural area is primarily associated with it?

Answer 15

Motion blindness, or akinetopsia, is the condition where an individual cannot perceive motion properly—seeing the world as a series of static images. This is most often due to damage to area MT, which is critical for processing visual motion

Question 16

How would damage to V1 affect an individual’s vision, particularly motion perception?

Answer 16

Damage to V1 generally renders an individual functionally blind since V1 is essential for processing basic visual information. Although some motion responses may persist via alternative pathways, overall vision is severely compromised

Question 17

Contrast the effects of losing V3 with losing area MT on motion perception

Answer 17

Losing V3 would impair the ability to perceive complex motion (especially concerning textured or complex moving stimuli) but would not completely abolish motion perception. In contrast, damage to area MT leads to severe motion blindness, highlighting its crucial role in directional and speed tuning

Question 18

What is the impact of losing MST/V6 with respect to motion processing?

Answer 18

Loss of MST and V6 primarily affects the processing of complex motion patterns and self-motion cues, thereby impeding effective navigation, even if basic motion perception remains partly intact

Question 19

What is the motion after-effect, and what neural mechanism explains it?

Answer 19

The motion after-effect is an illusion where, after prolonged exposure to motion in one direction, a subsequent stationary stimulus appears to move in the opposite direction. This occurs because the neurons tuned to the adapted direction reduce their firing (adaptation), skewing the balance of neural signals in favor of cells preferring the opposite direction

Question 20

what is the principle of univariance

Answer 20

a single motion-sensitive cell produces a one-dimensional output—its firing rate—that cannot independently distinguish between multiple stimulus attributes, such as contrast and speed

Question 21

How does the principle of univariance affect motion detection, specifically regarding speed and contrast?

Answer 21

The principle of univariance states that a single cell’s output is one-dimensional, meaning it cannot independently code for both the speed and the contrast of a stimulus. As a result, changes in contrast can be misinterpreted as changes in speed, since motion cells respond more strongly to high contrast and higher speeds—but they cannot separate these two variables on their own

Question 22

How is angular speed (in degrees per second) converted into linear speed, and why does viewing distance matter?

Answer 22

Linear speed depends on viewing distance. For example, 32 deg/s translates approximately to 0.57 m/s at 1 m, 2.85 m/s at 5 m, 5.7 m/s at 10 m, and 57 m/s at 100 m. The same angular speed corresponds to different linear speeds depending on the distance from the moving object

Question 23

How do motion cells respond to variations in contrast and speed?

Answer 23

Motion cells, especially in areas like V1, respond more vigorously to high-contrast and faster-moving stimuli. However, because of the principle of univariance, a single cell’s output does not distinguish between a change caused by increased contrast versus increased speed.

Question 24

What is induced motion (vection), and how does it affect perception?

Answer 24

Induced motion, or vection, is a phenomenon where a large field of moving visual stimuli leads the observer to perceive self-motion, even when stationary. This often happens in contexts such as being on a train, where the motion of the surrounding environment can create an illusion of movement and even result in a cue conflict with vestibular signals, sometimes causing sickness

Question 25

In the context of static images, what is illusory motion and what neural evidence supports it?

Answer 25

Illusory motion is the sensation of movement in a completely static stimulus (without any actual movement), beyond the typical motion after-effect. Evidence from studies—such as the activation of MT cells when viewing the Enigma illusion—suggests that over-excitation of orientation-sensitive cells (from regions like V1, V2, or V3) can erroneously activate motion-sensitive cells in MT, leading to the perception of motion.

Question 26

What is the aperture problem in motion perception?

Answer 26

The aperture problem arises when only a small part of a moving object is visible (as if viewed through a small aperture). V1 cells, with their small receptive fields, signal motion only perpendicular to the observed edge, leading to ambiguity about the object’s true direction. Area MT plays a key role in integrating these ambiguous signals to deduce the actual motion direction

Question 27

How does the pinna illusion illustrate the aperture problem?

Answer 27

The pinna illusion is demonstrated by diamond patterns whose edges stimulate V1 cells. As the observer rocks back and forth, V1 cells respond based on the orientation of the edges (i.e., the motion is signaled at right angles to the edge). When these signals are integrated in area MT, they produce a perception of rotation (with discounting of any expansion or contraction), showcasing the solution—and sometimes the pitfalls—of the aperture problem.

Question 28

Provide a summary of the hierarchical pathway for motion detection in the brain

Answer 28

Motion processing starts in V1, where cells with small receptive fields detect basic motion signals. This information is refined in V2 and then processed in V3, which handles more complex aspects of motion. The pathway continues to V5/MT, where direction and speed are finely tuned through opponent motion detection, then to MST and V6, which manage complex motion patterns and self-motion cues, respectively. Finally, areas such as STS further integrate motion information. Meanwhile, the retina and LGN do not contribute motion-specific detectors, emphasizing the importance of cortical processing for motion perception.