Wolfe Chapter 8 Review Questions - Motion Perception

Front 1

Describe one challenge in building a motion detector.

Back 1

One challenge is that in such a mechanism should “listen” to two other cells from two locations in space and then compute the motion. However, this detection cell cannot simply add up excitatory inputs from the two other cells. Instead, additional components are needed to establish a working neural circuit, such as a delay cell and a multiplication cell.

Front 2

Describe the concept of apparent motion.

Back 2

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

Front 3

What is the correspondence problem of motion?

Back 3

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

Front 4

Describe the aperture problem.

Back 4

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 is ambiguous.

Front 5

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

Back 5

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

Front 6

What is a motion aftereffect?

Back 6

A motion aftereffect is the illusion of motion of a stationary object that occurs after prolonged exposure to a moving object. For instance, looking at the downward motion of a waterfall for a few moments and then looking at a stationary object will cause that object to appear to be floating upwards.

Front 7

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

Back 7

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—specifically, some area in primary visual cortex or later.

Front 8

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

Back 8

First-order motion is the motion of an object that is defined by changes in luminance. This is the sort of motion we normally see in everyday objects. Second-order motion is the motion of an object that is defined by changes in contrast or texture, but not luminance. Second-order motion is not generally seen outside of the laboratory.

Front 9

What is a texture-defined object?

Back 9

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

Front 10

How does optic flow help us navigate around the world?

Back 10

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.

Front 11

What is biological motion?

Back 11

Biological motion is the pattern of movement exhibited by humans and animals. It is different from the motion of nonliving things. Biological motion can be detected even when only looking at a series of points of light attached to the joints of a moving person or animal.

Front 12

Why is tau important to navigating in the real world?

Back 12

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.

Front 13

What is the focus of expansion?

Back 13

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.

Front 14

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

Back 14

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.

Front 15

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

Back 15

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

Front 16

What is the role of vergence eye movements?

Back 16

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

Front 17

Why is saccadic suppression important in motion perception?

Back 17

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.

Front 18

What kind of problem does the comparator solve?

Back 18

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. In this manner, the visual system can determine that an object is moving even if its retinal image is stable. 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.

Front 19

What neural mechanisms besides the comparator help compensate for retinal motion due to eye movements?

Back 19

Just before an eye movement is initiated, cells in parietal cortex undergo predictive remapping in which they shift their receptive fields to line up with the future point of fixation rather than the current point. The advanced processing of features around the new fixation point helps the brain to compensate for the massive changes in the retinal image due to the saccadic eye movement.

Front 20

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

Back 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.

Front 21

Describe what happens in the disorder called akinetopsia.

Back 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.