Chapter 8 Questions

Question 1

Describe one challenge in building a motion detector.

Answer 1

One challenge is that in such a mechanism, one cell should “listen” to two other cells from two locations in space and then compute the motion.

Question 2

Describe the concept of apparent motion.

Answer 2

Apparent motion is the illusory impression of smooth motion resulting from the rapidly alternating presentation of objects that appear in different locations.

Question 3

What is the correspondence problem of motion?

Answer 3

The correspondence problem of motion is the problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a particular feature from frame 1.

Question 4

What is the purpose of an aperture?

Answer 4

The purpose of an aperture is to allow only a partial view of an object. It is an experimental tool used to illustrate the aperture problem.

Question 5

Describe the aperture problem.

Answer 5

The aperture problem is the fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous.

Question 6

What happens when the magnocellular layers of the LGN are lesioned?

Answer 6

When the magnocellular layers of the LGN are lesioned there is an impairment of the perception of large, rapidly moving objects.

Question 7

What did Newsome and Pare’s research involving dot motion displays show?

Answer 7

Their research showed that monkeys could be trained to recognize the direction of global motion in correlated dot motion displays. Then, when the monkeys’ MT areas were lesioned, their ability to identify the direction of motion was impaired. This supports the idea that MT is critical for motion perception.

Question 8

What does interocular transfer tell us about the locus of motion aftereffects in the visual system?

Answer 8

Interocular transfer, which is the transfer of an effect from one eye to the other, tells us that the motion aftereffect must be reflecting the activities of neurons in a part of the visual system where information from the two eyes is combined.

Question 9

What is the difference between first-order and a second-order motion?

Answer 9

First-order motion is the motion of an object that is defined by changes in luminance. Second-order motion is the motion of an object that is defined by changes in contrast or texture, but not luminance.

Question 10

What is a texture-defined object?

Answer 10

A texture-defined object is an object that is defined by changes in contrast or texture, but not luminance.

Question 11

How does optic flow help us navigate around the world?

Answer 11

Optic flow is the changing angular position of points in a perspective image that we experience as we move through the world. By observing optic flow, we can tell what speed and direction we are heading in, allowing us to adjust our locomotion accordingly.

Question 12

What is biological motion?

Answer 12

Biological motion is the pattern of movement exhibited by humans and animals. It is different from that of nonliving things.

Question 13

Why is tau important to navigating in the real world?

Answer 13

Tau is a measure of how quickly an image is expanding on the retina and can be used to determine time to collision without having to estimate absolute distances or rates. The ratio of the retinal image size at any moment to the rate at which the image is expanding is tau. By calculating tau, the visual system helps us avoid collision, which is important for navigating in the world.

Question 14

What is the focus of expansion?

Answer 14

When an observer is in motion, the focus of expansion is the point in the center of the horizon from which all points in the perspective image seem to emanate. The focus of expansion is one aspect of optic flow.

Question 15

How do smooth pursuit eye movements help us perceive moving objects?

Answer 15

In smooth pursuit eye movements, the eyes smoothly track a moving object, allowing better extraction of visual detail from the object as well as providing an estimate of the object’s velocity.

Question 16

What is the role of the superior colliculus in the midbrain?

Answer 16

The superior colliculus is a structure that is important in initiating and guiding eye movements.

Question 17

What is the role of vergence eye movements?

Answer 17

Vergence eye movements are helpful when one is focusing on a near or far object. In this type of eye movement the two eyes move in opposite directions: they either diverge outward, or converge inward.

Question 18

Why is saccadic suppression important in motion perception?

Answer 18

Saccadic suppression is important in motion perception because it eliminates the “smear” from retinal image motion during an eye movement. Saccadic suppression is a brief reduction of visual sensitivity during a saccadic eye movement.

Question 19

What kind of problem does the comparator solve?

Answer 19

One problem the comparator solves is that of an object in motion appearing stationary because its motion on the retina is removed via smooth pursuit eye movements. When an eye movement is planned, one copy of the movement command goes to the eye muscles, and the other goes to an area of the visual system called the comparator. The comparator also compensates for retinal image changes caused by eye movements, thus inhibiting any attempt by other parts of the visual system to interpret such changes as object motion when really only the eyes moved and not the object.

Question 20

Which aspects of motion perception are evident at birth and which aspects develop later?

Answer 20

Reflexive eye movements to moving targets are present at birth and neurons in V1 have adultlike sensitivity to visual motion direction. However, sensitivity to global motion, motion-defined form, and biological motion all develop later.

Question 21

Describe what happens in the disorder called akinetopsia.

Answer 21

Akinetopsia is a rare neuropsychological disorder in which the affected individual has no perception of motion. They experience a succession of static images but cannot perceive the motion connecting them.